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World List abbreviation: Bull. nat. Hist. Mus. Lond. (Zool.)

Zoology Series

ISSN 0968 — 0470 Vol. 61, No. 1, pp. 1-90

The Natural History Museum

Cromwell Road

London SW7 5BD Issued 29 June 1995

Typeset by Ann Buchan (Typesetters), Middlesex

Printed in Great Britain at The Alden Press, Oxford

Bull. nat. Hist. Mus. Lond. (Zool.) 61(1): 1-10

Issued 29 June 1995

A revised familial classification for certai

cirrhitoid genera (Teleostei, Percoidei

THE NATURAL

Cirrhitoidea), with comments on the group’s: JUL 1995

monophyly and taxonomic ranking

PRESENTED

GENERAL LIBRARY

P.H. GREENWOOD" ,

) [tie ey

Lato

B Rod

Honorary Research Associate, J.L.B. Smith Institute of Ichthyology, Private Bag 1015, Grahamstown

6140, South Africa and Visiting Research Fellow, The Natural History Museum, Cromwell Road,

London SW7 5BD

CONTENTS

MANU CLG O ig Pep ho csactineiractsltanis seigaresa ois dates guise sicisslse tee asada ati digecancipMienpiecaigi angjaasisicedtlessudeemancdcepseaddameceareeseegeadest 1

NACHO SAR OM ALC ASME rac iaadc tect Giaecaet y ontiveee snc acca Uick aoaeepteitmncenecrearccersech senteraetereseteraccavommecatecrerreersme 2

Urohyal morphology and the suprageneric classification of the cirrhitoid fishes, particularly the genus

Acantholatris and species currently referred to the genus Nemadactylus ............c.ccc0cceeceeneceeeeeneceeneceeees 2

The familial classification of Acantholatris Gill, 1862, and Nemadactylus Richardson, 1839 .............2....00e000- 5

Possible lineages within the Latridae as now expanded to include the genera Acantholatris and

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MAX GMOMNEATICMPHYVIOPEMEUEICONCIUSIONS 9.2.20. os coe vocencile Sap babip ob mete soaetinnehajad setesepienpsiadt se-edasinsspetionie des sisweins 6

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MATA CLOUPILe At OUSHIPS WALAINNEMS! CLT OLGS Hae teach access neeceweoeenerosecteidesetecenonsset saddle dovescenesscesensedeeatuernn 8

PRGRMOWICCPEMIEMES ar cre dena sno cecal dt de demon cay svsisissls «sciveesinaponavs ace uastiddecioe sais suletinentea t deaacisanlarec sects secure se ieee es 9

FRCLELCLICES Peper, oc ctu dieters Uae RCINAS NT TUN Adina «nis sein eneincadewaguassasedte cavdslamtaledaschaniia sveswscaedsantyevsegeseeetes serene ete 10

Synopsis. Previous suprageneric classifications of cirrhitoid fishes were based mainly on superficial characters.

Recent anatomical studies show that five morphologically distinct types of urohyal bone occur within the group, and

that on this basis certain taxa have been misplaced at both the generic and familial levels. The monophyly of the

cirrhitoid fishes, tacitly assumed by previous authors, is reviewed, and an hypothesis of their monophyly erected on

the basis of several synapomorphic features. It is also proposed, on the basis of those synapomorphies, that the

lineage be given subordinal rank within the Perciformes.

INTRODUCTION

During an investigation into the cranial and branchial muscles

associated with feeding in certain cirrhitoid fishes from South

African waters, it became apparent that five distinct morpho-

types of urohyal occur within the group. Two very distinct

types are found in genera currently classified as members of

the Cheilodactylidae; of these two forms, one also occurs in

genera referred to the family Latridae by Regan. Despite the

passage of over 80 years since Regan’s (1911) paper was

published, it remains the most recent suprageneric classifica-

tion of these fishes, which he arranged in five families, viz

Cirrhitidae, Cheilodactylidae, Aplodactylidae, Chironemidae

and Latridae, grouping them informally as the ‘cirrhitiform

percoids’.

Like its predecessor, namely Gill’s more detailed paper of

1862, Regan’s later analysis was based mainly on external

+ Dr Greenwood died 3 March 1995.

features. Apart from some comments by Regan on cranial

features, vertebral numbers and vertebral morphology, nei-

ther paper included any other anatomical information on

these fishes.

Although Regan (1911) expressed some doubts about the

familial status given by him to the five generic assemblages he

recognised (suggesting that subfamilial rank could be more

appropriate) he did not comment on Gill’s (1862) earlier

classfication which recognised four subfamilies within a single

family, the Cirrhitoidae; indeed, and inexplicably, Regan

(op. cit.) makes no reference at all to Gill’s paper.

Gill’s (op.cit) four subfamilies correspond, almost entirely,

to Regan’s families, except that Gill’s Latridinae included

two genera, Nemadactylus Richardson, 1839, and Cheilodac-

tylus Lacépéde, 1803, which Regan incorporated in his family

Cheilodactylidae; Gill’s list of included taxa in his concept of

the Latridinae also contained two genera not mentioned by

Regan, despite their being recognised at that time and still

being recognised today (viz Latridopsis Gill, 1862, and Acan-

tholatris Gill, 1862).

HISTORY MUSEUM

The present contribution, it is hoped, will play some part in

rewakening an interest in a phylogenetically based taxonomy

of Regan’s ‘cirrhitiform percoids’, and of their interrelation-

ships within, or perhaps outside, the Percoidei. Regan (1911)

gave no formal suprafamilial ranking to his ‘cirrhitiforms’,

but in some recent classifications (Nelson, 1994) the group

has been raised to a superfamily, the Cirrhitoidea. The use of

the terms ‘cirrhitoid’ and ‘cirrhitoids’ in this paper is thus to

be interpreted as a reference to the superfamily and not to the

suborder suggested for these fishes on p. 9.

METHODS AND MATERIALS

Species of the percoid families Serranidae and Centropomi-

dae served as outgroup representatives of basal members of

the Percoidei. The condition and composition of the sterno-

hyoideus muscles, and the morphology of the urohyal in these

taxa were taken to represent the plesiomorphic percoid

conditions.

Wherever possible, dry skeletal preparations and alizarin

transparencies were examined, as were radiographs and

dissections of preserved specimens.

STUDY MATERIAL. The symbols used in the following list are:

D. Sternohyoid muscle dissected and the urohyal removed or

examined in situ; X. Radiographed; S. Dry skeletal material

examined; an asterisk following a binomen indicates that this

name appears on the box housing the skeleton, and that its

specific identity could not be checked on the basis of the

characters preserved.

The familial grouping used in the list is that resulting from

the conclusions reached in this paper, and thus differs in some

respects from the classifications of Gill (1862) and Regan

(1911), and in some cases that of later authors (see p. 5

relating to the species ‘bergi’ and ‘gayi’ previously placed in

the genus Cheilodactylus and in the family Cheilodactylidae).

Institutional abbreviations are: BMNH, The Natural His-

tory Museum, London; DIFS, The Department of Ichthyol-

ogy and Fisheries Science, Rhodes University, South Africa;

RUSI, J.L.B. Smith Institute of Ichthyology, South Africa;

SAM, South African Museum, Cape Town.

STUDY MATERIAL.

(i) Outgroups.

Centropomidae; Glaucosomatidae; Ambassidae: The osteo-

logical and other material listed in Greenwood (1976).

Serranidae: as above, together with Epinephalus alexandri-

nus BMNH 1867.2.1: 69-72; (D).

(ii) Cirrhitoid fishes.

Aplodactylidae: Aplodactylus punctatus * (type species of

the genus): BMNH 1873.4.3: 157 (S).

A. lophodon: BMNH 1914.8.20: 214 (D).

Cheilodactylidae: Cheilodactylus fasciatus (type species of

the genus): 3 specimens, DIFS unregistered (D).

C. fuscus: 1 specimen, DIFS unregistered (D).

C. pixi: 6 specimens, DIFS unregistered (D).

2 specimens, DIFS unregistered (S).

4 ‘paperfish’ larvae, 44-50 mm standard length,

RUSI 19842 (D).

1 ‘paperfish’ larva, 44 mm standard length, RUSI

19842 (S).

C. zonatus: BMNH 1907.12.23: 238 (S).

P.H. GREENWOOD

Chirodactylus brachydactylus: 3 specimens, DIFS

unregistered (D).

2 specimens, DIFS unregistered (S).

2 ‘paperfish’ larvae, 33 & 38 mm standard length.

RUSI, unregistered (D).

C. grandis: 1 ‘paperfish’ larva, 57 mm standard

length. RUSI 18404 (D).

Dactylophora nigricans*: BMNH 1869.2.24:8 (S).

Chironemidae: Chironemus —marmoratus*: | BMNH

1871-3.29: 28)(S).

Chironemus marmoratus: BMNH 1861.11.7: 6 (D).

Cirrhitidae: © Amblycirrhitus pinos: 2 alizarin preparations

ex BMNH 1976.7.14: 453-7 (S).

Amblycirrhitus pinos: BMNH 1984.7.16: 96 (D).

Cirrhitus maculatus*: BMNH unregistered (S).

Cirrhitichthys oxycephalus: RUSI 11658; BMNH

1929.9.20: 8 (D).

Cirrhitichthys oxycephalus: BMNH 1908.3.23: 77-79

(X).

Cyprinocirrhites polyactis: RUSI 12339 (D).

Gymnocirrhites arcatus (type species of the

genus): BMNH 1965.12.20: 10 (D).

Gymnocirrhites arcatus*: BMNH unregistered, col-

lected by Richardson (S).

Gymnocirrhites arcatus: BMNH 1865.3.2: 82-83 (X).

Oxycirrhites typus (type species of the genus):

BMNH 1929.6.12: 2 (D).

Paracirrhites forsteri: BMNH 1852.9.13: 119 (S)

Paracirrhites forsteri: BMNH 1969.7.16: 28-32; one

specimen(D).

Acantholatris bergi BMNH 1936.18.26: 439 (D)

& (X).

Acantholatris gayi: BMNH

1890.2.26: 49 (D) & (X).

Acantholatris monodactylus (type species of the

genus): BMNH 1960.1.8: 6-13; one (D), all (X).

Acantholatris monodactylus: BMNH unregistered,

ex Gough Isl.; 2 specimens,both (S).

Acantholatris monodactylus: RUSI 33484; 33485;

33624 (D).

Latridopsis ciliaris (type species of the genus):

BMNH 1872.7.1: 32 (S).

Latridopsis ciliaris: BMNH 1873.12.13: 55 (D) &

(X).

Latris lineata: BMNH 1855.9.19: 124 (D).

Latris lineata: SAM 22623 (D).

Mendosoma lineatum (type species of the genus):

BMNH 1960.1.8: 14-21; one (D), all (X).

Mendosoma lineatum: RUSI 33613; 33625 (D).

Nemadactylus macropterus: BMNH 1855.9.19: 314

(X).

Nemadactylus macropterus: BMNH _ 1872.7.1: 21

(D) & (X).

Latridae:

1879.5.14: 278;

Urohyal morphology and the suprageneric

classification of cirrhitoid fishes, particularly the

genus Acantholatris and species currently referred

to the genus Nemadactylus

Within the cirrhitoid fishes, five morphologically distinct

types of urohyal can be recognised (Figs 1 & 2). Since each

REVISED CLASSIFICATION FOR CERTAIN CIRRHITOID GENERA

Fig. 1 The urohyal of:A. Paracirrhites forsteri; Cirrhitidae; left lateral view (BMNH 1852.9.13: 119). B. Chironemus marmoratus;

Chironemidae; left lateral and ventral views. (BMNH 1871.3.29:28). C. Aplodactylus punctatus; Aplodactylidae; left lateral and ventral

views. (BMNH 1873.4.3: 157). D. Dactylophora nigricans; Cheilodactylidae; left lateral view. (BMNH 1869.2.24:8). Relative to other

figures, this bone has been rotated through 90° to the left; arrow indicates dorsal prominence. Scale in millimetres. Drawn by Gordon

Howes.

type can be correlated with one of the five family groups

recognised by Regan (1911), these will be referred to as the

cirrhitid, latrid, chironemid, aplodactylid and cheilodactylid

types respectively.

The cirrhitid type (Fig. 1A) appears to be a plesiomorphic

form, one fundamentally similar to that found in several basal

percoids (see Kusaka, 1974; also personal observations).

The latrid urohyal (Fig. 2) differs markedly from the

cirrhitid type, and also shows slightly more intrafamilial

variation, particularly with regard to its posterior margin’s

degree of indentation, the extent to which the ventral margin

is produced bilaterally into a narrow or broader shelf, the

extent to which the bone is produced ventrally, and whether

the bone’s upper margin is sharp or somewhat flattened. Like

the cirrhitid type, the latrid urohyal is also of a pleisomorphic

form, one occurring in such basal percoids as the Serranidae

and Centropomidae (Kusaka, 1974; Greenwood, 1976: 39,

fig. 21, and other personal observations).

Departure from the basal percoid form of urohyal is most

pronounced in the chironemid, aplodactylid and cheilodac-

tylid types of bone. In chironemids (Fig. 1B) the bone is

shallow, the ventral margin greatly flattened and expanded

bilaterally to form a broad shelf, while the dorsal margin is

also noticeably flattened and bilaterally produced into a shelf,

albeit one relatively narrower than that on the ventral aspect

of the bone; when compared with the urohyal in cirrhitids,

P.H. GREENWOOD

Fig. 2. The urohyal of four latrid species.A. Acantholatris monodactylus (BMNH unregistered; ex Gough Island); left lateral and ventral

views. B. Latris lineata (BMNH 1855.9.19:194); left lateral view. C. Mendosoma lineatum (BMNH 1960.1.8:14-21); left lateral and ventral

views. D. Latridopsis ciliaris (BMNH 1872.7.1:31); left lateral and ventral views. Scale in millimetres. Drawn by Gordon Howes.

the chironemid type is relatively foreshortened (cf Figs 1A &

1B).

A pronounced ventral shelf and overall foreshortening of

the bone is also characteristic of the aplodactylid urohyal

(Fig. 1C), but in this type the bone is relatively deeper than is

the chironemid urohyal, and the dorsal surface is produced

into only a narrow shelf.

When compared with all other types, the cheilodactylid

urohyal (Fig. 1D) is very distinctive. In lateral view it has

virtually the shape of an arrow-head with its tip directed

anteriorly, and with the two arms meeting at the somewhat

thickened apex from which a dorsally directed-process arises.

The anterior edges of both arms are slightly broadened to

form a very narrow bilateral shelf that does not quite extend

to the posterior tip of either arm. Although, morphogeneti-

cally, the cheilodactylid type of urohyal could be derived

from a latrid type by a marked anterior extension and

deepening of the latter’s posterior indentation, coupled with

an increase in the angle subtended by the two arms so

formed, the two morphotypes are readily distinguishable.

Interestingly, the urohyal in the so-called ‘paperfish’ juvenile

stage (see p. 7) of a 44 mm standard length Cheilodactylus

pixi Smith, 1980, resembles that of the latrid type more

closely than does this bone in larger specimens; nevertheless,

the upper and lower arms of the urohyal in the ‘paperfish’

stage are more widely separated, the division between them

extends further anteriorly, and the anterior body of the bone

is less compressed and more barrel-like than that in any of the

adult latrid urohyals I have examined.

In his monograph on urohyal bones Kusaka (1974)

described and illustrates this bone in Goniistius zonatus

(Cuv., 1839), a taxon now, and previously (Gill, 1862),

REVISED CLASSIFICATION FOR CERTAIN CIRRHITOID GENERA 5

referred to the family Cheilodactylidae (see Allen & Heem-

stra, 1976, for comments on the status of this genus; also p. 6

below). Kusaka, however, lists the species under the heading

Aplodactylidae. The bone depicted is certainly of the cheilo-

dactylid type and not of the aplodactylid type, and I presume

Kusaka’s placing the species in the Aplodactylidae is a lapsus.

This author (op. cit: ) also figured and described the urohyal

from a specimen supposedly of Cirrhitichthys aureus Temm.

& Schl., 1843 (Cirrhitidae). Unfortunately I have not been

able to examine a specimen of this species, but the bone

illustrated (and described as ‘shaped like a standing rat’) is

unlike that in any cirrhitoid taxon I have examined, particu-

larly amongst members of the Cirrhitidae and even in a taxon

such as Oxychirrhites typus Bleeker, 1857, whose elongate

and tubular snout is an unusual morphotype within both the

Cirrhitidae and the cirrhitoids as a whole. If Kusaka’s figure

and description are accurate and the specimen was correctly

identified, then a sixth and highly distinctive form of urohyal,

one far removed from that of other cirrhitids must be

recognised, and the higher taxonomic position of its possessor

or posessord be reconsidered (assuming, that is, the bone

Kusaka examined was not teratological or damaged during

preparation).

A typical cheilodactylid urohyal (Fig. 1D) occurs in all

members of the family (sensu Regan [1911] and subsequent

authors) I have examined apart from Nemadactylus and

members of the genus Acantholatris, viz the type species A.

monodactylus (Carmichael, 1818), and the species A. gayi

(Kner, 1869) and A. bergi (Norman, 1937).

Parenthetically it should be noted that A. gayi and A. bergi

were both placed in the genus Cheilodactylus, and the family

Cheilodactylidae, by Norman (1937). The former species was

later transferred by Fowler (1945) to the genus Acantholatris,

with no explanation given for the change, but was retained in

the family Cheilodactylidae. Neither author appears to have

been aware, however, that Gill (1862) had included Acantho-

latris in his subfamily Latridinae. Mann (1954: 266) followed

Fowler’s generic and familial placing of A. gayi, and listed the

species bergi under Acantholatris in the index to that publica-

tion. The reader is there referred to page 266 of the text. No

mention is made of A. bergi on that page, but on page 85 (op.

cit.) Acantholatris bergi Norman (the author’s name not

enclosed in brackets) is listed amongst the ‘Invasores del

Atlantico’. Mann (op cit.) is thus the first author to employ

this particular combination of names for the species. As

noted earlier (p. 1) Regan did not include Acantholatris in

any of his cirrhitiform families.

The familial classification of Acantholatris Gill,

1982 and Nemadactylus

The urohyal in all three Acantholatris species examined, and

in Nemadactylus macropterus, is virtually identical and differs

markedly from that in the cheilodactylids, cirrhitids, aplodac-

tylids and chironemids (see pp. 2-5 and cf Fig. 1 with Fig.

2A). Instead, it resembles the latrid type, both in detail and

in its gross morphology (cf Figs. 2A, B and C), especially in

its fan-like outline. This marked difference would suggest

that the latrid genera (as listed in Regan, 1911), together with

Acantholatris and Nemadactylus shared a recent common

ancestry distinct from that of the cheilodactylids. It also

suggests that the phyletic relationships of the two groups are

obscured by uniting the cheilodactylids with the latrids in a

single subfamily, as did Gill (1862).

Thus, in my view, based essentially on their urohyal

morphology and not negated by other characters (see, how-

ever, the pectoral fin character discussed below), Acanthola-

tris and Nemadactylus should be included in the family

Latridae, currently comprising species of the genera Latris,

Latridopsis and Mendosoma, the latter recently shown to be

monotypic by Gon & Heemstra (1987). In addition to the

urohyal characters, the genera listed above lack a suborbital

shelf, which in cheilodactylids is a prominent feature formed

from the posterior upper margin of the lachrymal bone and

the entire upper margins of the second and third suborbitals.

Also, unlike cheilodactylids, these genera have the basal

scaly sheath to the soft dorsal fin somewhat higher and thus

more prominent than that at the base of the spinous part of

the fin.

As in cheilodactylids, the latrids (here taken to include

Acantholatris and Nemadactylus) have 35 vertebrae (14

abdominal + 21 caudal elements including the urostylar

element; data from radiographs and dry skeletons listed on

p. 2). To judge from the dry skeletal and dissected material

available to me, parapophyses are present on all precaudal

centra in both families, and no ribs are sessile.

Possible lineages within the Latridae as now

expanded to include the genera Acantholatris and

Nemadactylus

Acantholatris and Nemadactylus differ noticeably from Latris,

Latridopsis and Mendosoma in having one of the lower,

unbranched pectoral rays (i.e. the fifth, sixth or seventh ray

from the bottom of the series) greatly elongated, its tip,

which extends beyond the fin’s margin, reaching to at least

the level of the anus and sometimes as far as the midpoint of

the anal fin.

There are also differences in the following features:

(i) In scale size, as shown by lateral-line scale counts. In

Latris, Latridopsis and Mendosoma these range from 112 to

120 in the two former taxa, and from 68-78 in Mendosoma

(data from Last et. al., 1983; Gon & Heemstra, 1987;

pers.obs.). In Nemadactylus macropterus the count is 59 or

60, and in other species 47-68 (pers obs.; Last et. al., 1983)

and in Acantholatris monodactylus, A. bergi and A. gayi the

range is from 50-60 (Norman, 1937; pers. obs.).

(ii) Anal fin length. In Latris, Latridopsis and Mendosoma,

the number of branched anal rays ranges from 17-35 (the

lowest counts occurring in Mendosoma, viz. 17-21, whereas

in Acantholatris species and Nemadactylus macropterus the

range is from 12-15, and other species of the genus, 16-19

(sources as above).

Pending a detailed generic revision of the various taxa

involved, especially the several Australian and New Zealand

species currently referred to the genus Nemadactylus it would

be premature to formally recognise the two groups as, for

instance, tribes or subfamilies of the Latridae, although

phylogenetically some split seems to have occurred within the

lineage.

The condition of the pectoral fin in the Latris-Latridopsis-

Mendosoma group of latrids provides something of a puzzle

since these taxa are the only cirrhitiforms not showing any

marked elongation of the uppermost unbranched ray in the

lower section of the pectoral fin, nor, as in most other

cirrhitoids, do any of these rays clearly extend beyond the fin

membrane, and none is markedly thickened. In having the

lowermost 5-9 rays unbranched, these fishes are, however,

typically cirrhitoid. This latter condition can be considered

one of the synapomorphies uniting cirrhitoid fishes.

A typically derived pectoral fin configuration occurs in

the Cirrhitidae, yet the family would appear to be the least

derived of all cirrhitoid taxa (see p. 8). In contrast, except

for the condition of the pectoral fin, members of the

Latris-Latridopsis-Mendosoma assemblage within the

Latridae share with Acantholatris and Nemadactylus, and

with the cheilodactylids, aplodactylids and chironemids,

the derived condition for all the osteological and myologi-

cal features discussed on page 5. That being so, it is

unlikely that the pectoral fin form in Latris, Latridopsis

and Mendosoma can be interpreted as a true retention of

the plesiomorph condition. If that was the case, then the

derived condition must have evolved more than once

within the cirrhitoids. A more parsimonious solution to the

problem therefore, would, be to interpret the pectoral fin

form in Latris, Latridopsis and Mendosoma as a secondary

reversal to a seemingly more plesiomorphic condition than

is found in any other cirrhitiforms, including the family

with the greatest number of plesiomorphic features, the

Cirrhitidae (see p. 8).

The geographical distribution of the two groups within

the Latridae has an interesting pattern. Of the taxa in the

long-finned assemblage, Nemadactylus (see p. 5) occurs

only in Australia, Tasmania and New Zealand, thus over-

lapping the entire range of Latridopsis a member of the

short-finned group and one restricted to that region; it

overlaps in part (New Zealand and Tasmania) that of the

widely distributed Mendosoma lineatum, also a member of

the short-finned group, and in part, that of Latris, another

member of the short-finned group (Australia; New

Zealand; Gough and Tristan da Cunha islands; Vema

Seamount; St Paul and Amsterdam islands). The other

long-finned taxon, Acantholatris, does not occur in Aus-

tralasia, but has a wide western distribution, including St

Paul, Amsterdam, and Gough Islands, Tristan da Cunha,

Vema Seamount Chile, Juan Fernandez and the western

coast of South America from Rio de Janeiro southwards.

This distribution thus widely overlaps that of the short-

finned, monotypic genus Mendosoma lineatum, viz St Paul,

Amsterdam and Gough islands, the coast of Chile and, as

noted above, New Zealand and Tasmania (the latter being

areas where Acantholatris does not occur); data from

Norman, 1937; Fowler, 1945; Mann, 1954; Smith 1984;

Last et. al., 1983; Gon & Heemstra, 1987; Paulin et. al.

1989; Andrew & Hecht, 1992; Andrew, pers.comm., 1993).

TAXONOMIC AND PHYLOGENETIC

CONCLUSIONS

Taxonomy

The material studied indicates, on osteological and myologi-

cal grounds (p. 5), that the species currently named Nema-

dactylus macropterus (the type species of Gill’s (1862) genus

Dactylopagrus; see Wheeler, 1986) should be classified in the

Latridae and not the Cheilodactylidae as it is at present.

P.H. GREENWOOD

The genus Acantholatris Gill (1862, type species Chaetodon

monodactylus Carmichael, 1818), was overlooked by Regan

(1911) in his synoptic review of cirrhitoid families, but is

currently placed in the family Cheilodactylidae (see p. 5).

However, on the basis of its urohyal morphology, and its

lacking a suborbital shelf (see p. 5) the genus should be

classified in the Latridae. Regan (1911) differentiated the

Latridae from the Cheilodactylidae on the basis of the latrids

having feeble, unbranched pectoral rays that are not pro-

duced beyond the fin’s margin, and by their lacking a

suborbital shelf; in other feaures he noted that the two

families are similar. With the inclusion of Acantholatris and

Nemadactylus in the Latridae the nature of the pectoral fin no

longer serves as a differentiating feature (see p. 5), the

principal diagnostic characters for the family now lying in the

form of the urohyal bone, the absence of a suborbital shelf,

and in the more prominent arrangement of the basal sheath-

ing scales of the soft dorsal fin (see p. 5).

Gill’s (1862) suprageneric classification included Nemadac-

tylus as a division — Nematodactyli — of his subfamily Latridi-

nae, in which subfamily but as another division to which he

gave the name Latrides he also included Latris, Latridopsis,

Mendosoma, Acantholatris, Chirodactylus, Cheilodactylus

and Goniistius. Regan (1911) on the other hand, but without

reference to Gill’s paper, treated the latter author’s four

subfamilies as families, and recognised a fifth, the Cheilodac-

tylidae, for two genera, viz Cheilodactylus and Nemadactylus;

no mention is made in Regan’s paper of the other taxa in

Gill’s Latridinae except for Latris and Mendosoma, which

Regan retained in his family Latridae.

The evidence presented here (pp. 2-5), especially that

based on urohyal morphology, would support Regan’s (1911)

classification with regard to the separation of Cheilodactylus

(and, although not mentioned by Regan, Chirodactylus and

Goniistius) from the other taxa included in Gill’s Latridinae,

and would support the inclusion of all three taxa in one

family, the Cheilodactylidae. The same evidence would also

support Gill’s inclusion of Latris, Latridopsis, Acantholatris,

Mendosoma and Nemadactylus in a single suprageneric

taxon. Since Regan’s (1911) familial ranking has been

accepted and used since that time, and until contraindicative

evidence is available to suggest otherwise, that ranking (i.e.

Latridae) is retained.

The anatomical and other features used in this paper

(pp. 2-5) would support the recognition of Gill’s (1862) and

Regan’s (1911) other suprageneric lineages, again, for the

reasons given above, as families and not subfamilies, viz. the

Cirrhitidae, Aplodactylidae (Gill’s Haplodactylinae) and Chi-

ronemidae.

At an intrafamilial taxonomic level, Allen & Heemstra

(1976) note that ‘The currently accepted classification of the

Cheilodactylidae ... is most unsatisfactory’ a sentiment I

would not only endorse, but would extend to other cirrhiti-

form families as well. In part this situation has resulted from

the use of mainly superficial characters, with little or no

attention paid to anatomical features, especially myological

and osteological ones. Thus on those grounds I cannot agree

with Allen & Heemstra’s (op.cit.) treating Acantholatris as a

subjective synonym of Cheilodactylus and its consequent

placement in the Cheilodactylidae (see above, p. 5). How-

ever, at least on the characters and specimens I have exam-

ined, I would endorse their synonymy of Whitley’s (1957)

genus Morwong (type species Cheilodactylus fuscus Castel-

nau, 1879) with Cheilodactylus.

REVISED CLASSIFICATION FOR CERTAIN CIRRHITOID GENERA /

The cirrhitoids as a monophyletic lineage

On the basis of several apparently synapomorphic character-

istics (see below) the cirrhitoids would seem to be a mono-

phyletic lineage, a conclusion implied by both Gill (1862) and

Regan (1911) who described the group as a ‘natural’ one but

gave no reasons for that conclusion. The derived characters

on which I would base an hypothesised monophyly of the

cirrhitoids are, taken in conjunction, a reduced number (15)

of principal caudal fin rays, the unbranched lowermost five to

nine rays in the pectoral fin (usually with their tips produced

beyond the fin membrane), the lower part of each cleithrum

greatly expanded anteroposteriorly and meeting its antimere

in a deep, carinate symphysis, an increased number of

vertebrae relative to other percoids (26-35, comprising 10-16

abdominal and 15-21 caudal elements), and the presence,

ventrally, in subadults of a peculiar, lipoid-filled sac (Fig. 3),

free from the overlying hypaxial muscles, and extending from

the urohyal, to which it is attached, to the anus, with the

lipoidal material apparently contained in hexagonal compart-

ments.

To the best of my knowledge, this lipoid sac has not previ-

ously been noted as a feature of subadult cirrhitoid fishes, nor

indeed of any other perciforms except the stichaeid Lumpenus

maculatus (see Falk-Petersen et al., 1984). I first observed it in

small specimens (the so-called ‘paperfish’ stage) of Cheilodacty-

lus pixi ca 43 to 44 mm standard length (Fig. 3), where its

presence results in the ‘pouter-pigeon’-like ventral profile of the

paperfish stage in this and other cirrhitoid species (see photo-

graphs in Whitley, 1957; Allen & Heemstra, 1976, and Nielsen,

1963). Subsequent dissections revealed a lipoid sac in members

of all but two of the cirrhitoid families I have dissected (see

p. 2). The exceptions are a chironemid, Chironemus marmora-

tus Gunther, 1860 (160 mm standard length) and an aplodac-

tylid, Aplodactylus lophodon Ginther, 1859 (180 mm S.L.).

Since, however, the sac is a juvenile (i.e. sub-adult) feature in

the other taxa, and the exceptional specimens were, to judge

from their gonadial development, young adults, I suspect that it

would also be present in smaller specimens of these species. In

Cheilodactylus pixi, for example, the sac is well-developed in a

specimen of 44 mm standard length, but has disappeared in one

of 46 mm. Likewise, in Chirodactylus brachydactylus (Cuv.,

1830), it is present in a fish of 38 mm standard length, but absent

in one of 42 mm. The presence of a lipoid sac in specimens from

128 to 243 mm standard length of other species (referred in the

current literature to the Latridae and Cheilodactylidae) whose

maximum adult lengths are from 50 cm to one metre, suggests

that the size at which the lipoid sac disappears is positively

correlated with that at which members of a species become

adult. This supposition is borne out by the presence of the sac in

a juvenile Chirodactylus grandis (Gunther, 1860) of 57 mm

standard length, a species whose adults reach a length of one

metre, whereas it has disappeared, at a length of 42 mm, in

young Chirodactylus brachydactylus, whose adults reach a

length of 40 cm. Again, it is present in a specimen of Acanthola-

tris monodactylus 243 mm S.L.; adults of this species attain a

standard length of at least 65 cm. Thus, the sac’s apparent

absence in chironemids and aplodactylids could be artefactual,

and related to the size-range of the specimens I was able to

examine.

It is hoped to carry out a more detailed examination of the

lipoid sac when specimens suitably fixed for detailed histo-

Fig. 3 Chirodactylus pixi, 49 mm standard length (RUSI 19842) in right lateral view; partially dissected, and with the greater part of the

pectoral and the entire pelvic fin removed. The large anterior portion of the lipoid sac (LS) is clearly visible; part of its posterior portion is

also visible (x). Throughout its length, the wall of the sac, unlike the muscles above it, is heavily peppered with melanophores.

logical and histochemical study are available.

Intragroup relationships within the cirrhitoids,

and the ranking of the group

Within the cirrhitoids, the Cirrhitidae should be ranked as the

most plesiomorphic taxon, a view seemingly implicit in

Regan’s (1911) diagram of relationships. My reasons for

giving the family this ranking are based on urohyal form, the

low vertebral count (26-28) relative to that in other families,

the absence of parapophyses on the first three abdominal

vertebrae, sessile ribs associated with these vertebrae, the

presence of 3 predorsal bones (2 in the other cirrhitoids

radiographed or dissected) and the presence of a suborbital

shelf (which, however, is also developed in the Cheilodactyl-

idae [but see below]). Furthermore, the Cirrhitidae are the

only cirrhitoids with a basal percoid type of myotome

arrangement in the sternohyoideus muscle, a feature not

previously noted. That is, one in which the three pairs of

hypaxial myomeres forming the sternohyoideus muscle are all

arranged in a vertical series, with the first block covering the

anterior part of the urohyal (Fig. 4A). Members of all other

cirrhitoid families, in contrast, have the first (i.e. anterior)

hypaxial myotome of each side displaced ventrally so that it

now lies medially and horizontally (not, as in cirrhitids,

laterally and vertically) to form, with its antimere, a ventral

muscle, paired in most species but in some with the left and

right parts fused over most of their lengths to form a single

median muscle (Fig. 4B). Single or paired, this ventro-medial

component of the sternohyoid runs from the urohyal tip to

the prominent ventral projection at the symphysis of the left

P.H. GREENWOOD

and right cleithra, its origin thus being immediately before

that of the anterior infracarinalis muscle insertion.

In both the Cirrhitidae and in the other families, the

sternohyoideus myotomes, except the horizontal first myo-

tome in the latter group, are chevron-shaped with the apex

directed anteriorly. However, in the latrids, cheilodactylids,

chironemids and aplodactylids, the angle between the upper

and lower arms of the chevron is more acute, and the lower

arm is relatively longer than in cirrhitids.

Judging from the rather scant literature on the sternohyoid

muscle in teleosts (see Winterbottom, 1974), and from a

personal knowledge of the situation in percoids, the condition

of the muscle in the Cirrhitidae should be ranked as plesio-

morphic, that in the other cirrhitoid families as derived and

possibly a unifying synapomorphy for the Aplodactylidae,

Chironemidae, Latridae and Cheilodactylidae within the lin-

eage.

In Regan’s (1911) figure of cirrhitoid intrarelationships

referred to above, the Cirrhitidae occupy a basal (i.e. stem

position) and are linked, on the one hand to the Chironemi-

dae and Aplodactylidae, and on the other to the Cheilodac-

tylidae and Latridae (the generic composition of the families

being those given by Regan). No reasons were provided by

Regan for these supposed relationships, which presumably

were based mainly on superficial characters as well as a few

anatomical ones. With the anatomical information now avail-

able a different scheme of intragroup relationships at the

family level can be proposed (see Fig. 5, and Table 1).

In this scheme, apomorphic features (see Table 1) are

taken to be: (1) The derived form of urohyal, of which there

are three distinct types (see p. 3). (11) The presence of a

Fig. 4 A. Cirrhitid type organization of sternohyoid

myotomes. Drawn from Paracirrhites forsteri;

semi-schematic. In this arrangement, the

sternohyoid muscles completely envelop the urohyal

bone. B. Basic organization of the sternohyoid

myotomes in all other families. Drawn from

Nemadactylus monopterus; semi-schematic. In taxa

of these families, varying an terior extents of the

urohyal are not covered by the sternohyoid muscle.

1-4: 1st to fourth myotomes of the sternohyoid

muscle; c: cleithrum; ce: cut edges of the sterno-

hyoid myotomes; uh: urohyal. Drawn by Anthea

Ribbink

REVISED CLASSIFICATION FOR CERTAIN CIRRHITOID GENERA 9

@ ®

@ PN 4 o

@ oO” » xy

e . ree) (<

\y o @ a? P A

os of) ry <> oe

, 15 2,18 3* 15" 5

9”

1 or 2,6,8, 10,112,114

Fig. 5 Tentative scheme of phyletic relationships within the Cirrhitoidei. Asterisks indicate apomorphic characters (see also Table 1). Since

both the cirrhilid (1) and latrid (2) condition of the urohyal are rated as pleisomorphic, that bone in the common ancestor of all lineages is

taken to be 1 or 2.

derived myotomal arrangement of the sternohyoideus

muscles (p. 8). (iii) More than 28 vertebrae. (iv) Parapophy-

ses developed on the first three abdominal vertebrae, with

the first pleural rib associated with the second or third

vertebrae. (v) Predorsal bones reduced to 2. The three

different types of derived urohyal morphology (pp. 2-5) (ie in

chironemids, aplodactylids and cheilodactylids) are each

taken to be independently evolved apomorphies. Relation-

ships (Fig. ) suggested by these data are: (i) That the

cirrhitids are the plesiomorph sister group to the other four

families combined. (ii) The chironemids are the sister taxon

of the aplodactylids, latrids and cheilodactylids combined,

and that for the moment this assemblage should be treated as

an unresolved trichotomy since no two lineages uniquely

share a recognisable synapomorphic feature. For example,

the urohyal in the latrids is of a basal percoid type, and

although that bone in the cheilodactylids and aplodactylids is

highly derived, each is unique to the families respectively.

The cheilodactylids it will be noted, retain the plesiomorphic

suborbital shelf, whereas it is lost in the latrids and aplodac-

tylids (and in the chironemid lineage as well). The value of

this feature as an indicator of relationship, however, is

problematical because it involves a loss (and not an acquisi-

tion) in the lineages concerned. Clearly, a greater number

and variety of characters must be sampled and their polarity

determined before this hypothesis of cirrhitoid intrarelation-

ships can be improved and the trichotomy resolved.

The same reservation would apply before any sister-group

hypothesis can be erected regarding the relationships of the

citrhitoids within the Percomorpha. However, based on the

synapomorphic features discussed (above pp. 6-7) it seems

reasonable to hypothesize that the five families comprising

the lineage, given informal ranking as the ‘cirrhitiform per-

coids’ by Regan (1911), and suprafamilial status by recent

authors (Nelson, 1994), should be elevated to subordinal

status (Cirrhitoidei) within the Perciformes.

ACKNOWLEDGEMENTS. I am particularly indebted to Dr Colin Buxton

of Rhodes University’s Department of Ichthyology and Fisheries

Science who first aroused my interest in the anatomy of cirrhitoid

fishes, and who provided many specimens for dissection. Professor

Tom Hecht of that department is to be thanked for personally

obtaining a specimen of Cheilodactylus fuscus from Salamander Bay,

New South Wales, in which operation he was aided by Bill Talbot of

the Brackish Water Fish Culture Research Station there.

To Dr Phil Heemstra of the J.L.B. Smith Institute goes my

gratitude for the many discussions we have had about cirrhitoids, and

for his advice on the relevant literature, and to Tony Booth of DIFS

my appreciation for his painstaking preparation of several skeletons.

Once again it is a great pleasure to thank my old colleague Gordon

Howes for his elegant and accurate draftmanship, and also to thank

another former colleague, Oliver Crimmen of the Fish Section, The

Natural History Museum, London for his untiring help with matters

radiographic and bibliographical. Yet again, my special thanks go to

Huibre Tomlinson, for her patience and skills in producing the

typescripts, and to Robin Stobbs for producing certain of the

radiographs, and the photograph, used in this paper.

Table 1 Data matrix and characters.

P.H. GREENWOOD

Cirrhtidae

Amblycirrhitus pinos sie 0 0 0 0

Cirrhitus maculatus oF 0 0 0 0

Cirrhitichthys oxycephalus + 0 0 0 0

Cyprinocirrhites polyactus ar 0 0 0 0

Gymnocirrhites arcatus + 0 0 0 0

Oxycirrhites typus + 0 0 0 0

Paracirrhites forsteri + 0 0 0 0

Chironemidae

Chironemus marmoratus 0 0 0 + 0

Latridae

Acantholatris bergi 0 + 0 0 0

A. gayi 0 al 0 0 0

A. monodactylus 0 + 0 0 0

Latridopsis ciliaris 0 + 0 0 0

Latris lineata 0 + 0 0 0

Mendosoma lineatum 0 aF 0 0 0

Nemadactylus macropterus 0 ate 0 0 0

Aplodactylidae

Aplodactylus punctatus 0 0 + 0 0

A. lophodon 0 0 + 0 0

Cheilodactylidae

Cheilodactylus fasciatus 0 0 0 0 ae

C. fuscus 0 0 0 0 +f

C. pixi 0 0 0 0 +

C. zonatus 0 0 0 0 +

Chirodactylus brachydactylus 0 0 0 0 ar

C. grandis 0 0 0 0 +

Dactylophora nigricans 0 0 0 0 sf

t+++4¢4+4++

ooooctocto

t++tt+e+

Se Ser) ju)

t+t+¢4¢4¢4+4+

SPSS) (Say TS) (=)

t+tt+tt+

SSS Sh}

t++t++4++

(J) i) —)

(=)

S51 ors)

t++++t+4++

SS) (=) Sy SSS)

t+4+4+4+44

Sears SiS

t+tt¢t4¢+

SS) Seer)

P+ett+tet

SSS: ior

t+tttttt+

(SS)

+ +

SS) SY Sy)

+++4+4+4++

Seat eSyere) &)

+++4+4+4+4

SSS Sree)

t++tt¢4+44

(=) faa) (=) [Si ) tS}

+++4+4+4+4+

t++t++44

SSS. eS 1

Characters: 1. Cirrhitid-type urohyal (i.e. of a basal percoid type, but one differing from the latrid condition); 2. Latrid-type urohyal (i.e. of

basal percoid type; see 1); *3. Aplodactylid-type urohyal; *4. Chironemid-type urohyal; *5. Cheilodactylid-type urohyal; 6. Less than 28

vertebrae; *7. More than 28 vertebrae; 8. Parapophyses not developed on the first three (sometimes 4) abdominal vertebrae, but sessile

pleural ribs on one or two of these centra; *9. Parapophyses developed on the first three abdominal vertebrae. No sessile pleural ribs; 1st

pleural rib articulating with the parapophyses of the third abdominal vertebrae; 10. Three predorsal bones; *11. Two predorsal bones; 12.

Basal percoid-type of sternohyoid muscle; *13. Derived condition of the sternohyoid muscle; 14. Suborbital shelf present; *15. Suborbital

shelf absent. Asterisk indicates an apomorphic feature.

REFERENCES

Allen, G.R. & Heemstra, P.C. 1976. Cheilodactylus rubrolabiatus, a new

species of Morwong (Pisces:Cheilodactylidae) from Western Australia, with

a key to the Cheilodactylid fishes of Australia. Records of the Western

Australian Museum, 4(4): 311-325.

Andrew, T.G. & Hecht, T. 1992. Feeding biology of Acantholatris monodacty-

lus (Pisces:Cheilodactylidae) at Tristan da Cunha and Gough Island, South

Atlantic. South African Journal of Antarctic Research, 22: 41-49.

Bloch, M.E. & Schneider, J.G. 1801. Systema ichthyologia. 584 p. Berolini.

Falk-Falk-Petersen, S., Falk-Petersen, I-B, & Sargent, J.R. 1986. Structure and

function of an unusual lipid storage organ in the arctic fish Lumpenus

maculatus Fries. Sarsia, 71: 1-6.

Fowler, H.W. 1945. Fishes of Chile. Systematic catalog. Apartado de la Revista

de Historia Natural, Anos XLV-XLVII: 1-171.

Gill, T.H. 1862. Synopsis of the family of cirrhitoids. Proceedings of the

Academy of Natural Sciences of Philadelphia 14: 102-124.

Gon, O. & Heemstra, P.C. 1987. Mendosoma lineatum Guichenot 1848, first

record in the Atlantic Ocean, with a re-evaluation of the taxonomic status of

other species of the genus Mendosoma (Pisces, Latridae). Cybium 11 (2):

183-193.

Greenwood, P.H. 1976. A review of the family Centropomidae (Pisces,

Perciformes). Bulletin of the British Museum (Natural History) Zoology 29:

1-81.

Kusaka, T. 1974. The urohyal of fishes. xiv + 320 p. University of Tokyo Press,

Tokyo.

Last, P.R., Scott, E.O.G. & Talbot, F.H. 1983. Fishes of Tasmania, viii + 563

p. Tasmanian Fisheries Development Authority, Hobart.

Mann, G. 1954. Vida de los Peces en aguas Chilenas. 342 p. Ministero de

Agricultura and Universidad de Chile, Santiago.

Nelson, J.S. (1994). Fishes of the world; 3nd edition. xviit+600 p. J. Wiley &

Sons, New York.

Nielsen, J.G. 1963. On the development of Cheilodactylus variegatus Valenci-

ennes, 1833 (Cheilodactylidae) Copeia 1963(3): 528-533.

Norman, J.R. 1937. Coast fishes, part II. The Patagonian Region. Discovery

Reports. 16: 1-150.

Paulin, C., Stewart, A., Roberts, C. & McMillan, P. 1989. New Zealand fish, a

complete guide. National Museum of New Zealand, Miscellaneous Series. ,

no. 19: xiv + 279.

Regan, C.T. 1911. On the cirrhitiform percoids. Annals and Magazine of

Natural History (8)7: 259-262.

Smith, M.M. 1984. Cheilodactylidae. Jn: Fishcher, W. & Bianchi, G. (eds).

FAO identification sheets for fishery purposes, western Indian Ocean. F.A.O.

Rome.

Wheeler, A.C. 1986. Catalogue of the natural history drawings commissioned

by Joseph Banks on the Endeavour voyage 1768-1771, held in the British

Museum (Natural History). Part 3: Zoology. Bulletin of the British Museum

(Natural History) Historical Series 13: 1-172.

Whitley, G.P. (1957). Ichthyological illustrations. Proceedings of the Royal

Zoological Society of New South Wales, 1955-56: 56-71.

Winterbottom, R. 1974. A descriptive synonymy of the striated muscles of the

Teleostei. Proceedings of the Academy of Natural Sciences of Philadelphia

125: 225-317.

Bull. nat. Hist. Mus. Lond. (Zool.) 61(1): 11-90

Studies on the deep-sea Protobranchia

(Bivalvia); the Subfamily Yoldiellinae

J.A. ALLEN

University Marine Biological Station, Millport, Scotland KA28 0EG

H.L. SANDERS

Woods Hole Oceanographic Institution, Woods Hole, Mass., 02543, U.S.A.

F. HANNAH

University Marine Biological Station, Millport, Scotland KA28 0EG

Kev

Issued 29 June 1995

CONTENTS

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Waldiellaiinconspicudiinconspicua Vertill/ GeNBUSDEMNB98: «ccc. asucneqscescaescoecesccesaseranenrceniessesacdesvvsestaseusie 41

WMelaielianmnaanSpIcua G/TiCANnd (GMEW:SIDSPECIES)) ook. ccscesncsentccstceseseasscnedascavscuccstcmeccdessncsecarceacssssccoers 44

WOldICHGNHEONSPIGUG PrO;UNAOTUMM (MEWISUDSPECIES) ....cce-ceeddeescae daca tcvc-ceceeocaasecesnossccduncarcadeecsesnaseents 45

MOIGIEIGTEEMITILETISIS (EW SPECIES) Mente eeattes. .aens «snscrnetmess cosesesssorcgeutnnstccesacaeceesdeacssecnsacessueeeccnsaees 46

MOEN CMa WELul GES USMe LOGOM cutee satetee Ast snceccatenecatceecagcceacedevetetercecasttecdtertetestesstaccerecet ters 47

Woldrellanperplexdl(MEW SPECIES)! . costmcete treme ence teens ccatnares -grecesadercncccrematecdescacscdeshorcecsdcucecutreueseseness 51

CITE AaINENIGANG\ MEW SPECIES Mpre eae eeccte arctan «anc .deeesee arte we teete sas ac eaten Mere tame cnee erecta stent oeae cies 52

Moldiclasubcircnlaris (Odiiner 1960); tte. settee eee «now ata Eee Eee ee Oe See 54

ial diellaaDy 2uitaral (EMI SPECIES) We metre: tater et ceee «cas wnnc eke etb atts svasnpatcces Me meewena debe wa hthecec sates ae eee noes 57

MolatellaOvalal Mew SPECIES) Werte sa eee seer Merten cto cakes «na acide Cae thes cane een note ee ee ee eee 59

WOGIGIATISCHIING (USIUENIER INST) [ebeaqoaacenaStic soon Caine ER A bake Rata aae opcebac ance: Bac coGrrEE ade SaEoun ee cL EReencseectrdee 60

Moldiellanenfrey sia (El dal oOM Si) crnacenaen ances tase. «x's» cea rneeceeene aaah beets See cace «= see same teee ae ee a otellrne saat 63

MOlAI CU CNC HAIGA (MEW SPECIES) cheese sates ceteris, asia ss'ssw acs ROSA TSE e OSS aR a SRR RE te lear 68

Nal diellateliad (Me WwaSPECIES) laserctee tet cc. castes erateet «5. cA Pe RE Pere, seat tls . Feta Samer he dee eles 70

Ne etal at abil ad (HEWES DECIES) tesa sene cece eee are erie nee cine dbmeunnt deems aus siocusbins ne jaz tae skiasinlc sine oa meereRiatan semua ee 73

Woldiallanpeletiah(ME wy SPECIES) te Met ceed oP octane ee «ic «- «Rae eetae Aeataaeerseomraeeaeae atntairmierdna baba daany daerstamprns oem 76

GenusHZorilandigi(NIGrehal BO) rasan caatsns tees acrseeom eso: wc ts eM Gs Selecta as ROP Sat Me MER Aa AH a 77

ROTI Ai GR CITC! an NAOMI spl OAD) bracers ate cb a tae Sak nes 05 RSet 1a See whe eine ae aes ts ata asaya siueaelo oasgarceebeecae 77

HZOTE AIG Ch) OV. Gl WE WASP GIES) [Meter cays sn ise few te ts aac ic Se carceraai see ai ghia sole ees Bp oats seat < sisal eeaase aaa ceietsduea 78

BOF LETC LCMEPPERLELICLA (HIE WAS PIE CLES) Eee meee facia as os scl ceieaeles alse ciesialus ost sis oath oenelad Ohm Ras wacewigs beh cen seceeee Be 80

ROTA CLA DUS OTT (INTAUOSE Diss OF.) ua ceerce tae tesastaas ss see aaa ae ceases see cae ae ea essai oma VOSS SEES GEE See 81

ISIS GLSS1 Tite ee tet eee ae eae ere eet as core cl Se ers iat ose et eat enc MER DARE Meche Gee sc coe Se ceacsnsiemn se maningerceess 82

RCL CTCM CC Sterne MeeReRee ce eee eRe e cee aeer nc re Cee eee such ns dose cies mavecdetinet Hadeandenecvannerroneenssstersqueiece ss ceuer 90

24 Lo

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Synopsis. Four species of the genus Portlandia and twenty-nine species and five subspecies of the genus Yoldiella

from the deep Atlantic are described — many for the first time. The subfamily Yoldiellinae includes more species

than any other higher taxon of deep-sea protobranchs. The differences in morphology are for the most part subtle

and there are many closely related species. These close relationships have been analysed, the analysis taking into

account shell shape, hinge morphology, musculature and the extent and course taken by the hindgut. Taken

together with geographical and depth distribution a pattern of evolution is derived. This supports the view that the

derivation of the deep-water species of Yoldiella in the Atlantic has been derived mainly via downslope migration

and speciation rather than by deep water migration from the Southern Ocean.

INTRODUCTION

This is the eighth paper in a series on the biology and ecology

of the deep-sea protobranch bivalves of the Atlantic (Allen &

Sanders, 1973, 1982; Allen & Hannah (1989); Rhind & Allen

(1992); Sanders & Allen 1975, 1977, 1985. Our interest is

widespread and includes, ecology and adaptations to life at

great depths, morphology, reproduction, distribution and

evolution. Here we turn to the subfamily Yoldiellinae and

what has become our major and most difficult task of all our

protobranch studies to date. Nowhere have the problems of

elucidating evolutionary trends and specific and subspecific

divisions within the Protobranchia been so acute as in this

large group. Of necessity descriptive and taxonomic studies

have played a major role in all our studies. This is because so

many species from the deep oceans are new. Now that we

have studied more than three quarters of the protobranch

material in our collections, it has become obvious that major

questions on the evolution of the subclass — particularly those

taxa in the deep ocean — remain to be answered. We have

described (Sanders & Allen, 1985) intra- and _ inter-

population variations in various species and the difficulties in

separating even higher taxa with satisfactory, clear cut,

definitions (Allen & Hannah, 1986). These difficulties can be

no better illustrated than in our studies on the Yoldiellinae. A

considerable effort has been put into the analysis of the most

subtle differences in shape and form of the many species of

the subfamily. As a consequence we have decided to record

our observations in two parts. In the first, here, we describe

36 species in a way that has become standard for this series of

papers, describing those population variations that are perti-

nent to description and taxonomy. In the second, we will

report in detail on diversity and the quantitative aspects of

the ecology of sibling species which are distributed widely in

many Basins of the Atlantic.

Species of the subfamily Yoldiellinae, are among the most

common protobranchs of the deep sea and many are recorded

in the literature. The difficulties we have experienced in

accurately distinguishing the species is not new and confusion

is apparent in both past and recent literature and in museum

identifications of this group.

Descriptions of genera and higher taxa are based on the

recent studies of Shileiko (1985) and Allen & Hannah (1986),

but complemented from the results of this study. Holotypes

have been lodged in either the Natural History Museum,

London, or the Museum National d’histoire Naturelle, Paris.

The paratypes, together with the remainder of the specimens

collected, for the time being are in the care of JAA, but at the

conclusion of the studies will be lodged in appropriate

Museums.

Measurements of height, length, width and postumbonal

length have been taken and in the case of larger samples

ratios have been plotted. For species of which we have few

specimens the measurements have been tabulated. While

these record the variation in the major axes, they do not

measure subtle variation in shell outline and curvature. Much

time has been spent on computerized analysis of shell shape

and on this work we hope to report later but, to date, this has

not improved on visual recognition from comparative accu-

rate drawings. We prefer drawings to photographs for their

clarity.

In recognizing subspecies we comply with the ICZN.

Subspecies occur at different depth ranges and/or different

basins. In a few cases we recognize ‘forms’, infrasubspecific

units which, in compliance with ICZN, cannot clearly be

distinguished in their distribution patterns but which may

indicate a species in the process of subspeciation.

ABBREVIATIONS TO TEXT FIGURES

AA anterior adductor muscle ME mantle edge

AN anus MT major typhlosole

AS anterior sense organ NV nerve

BG ‘byssal’ gland OE oesophagus

CG cerebral ganglion PA posterior adductor muscle

CS combined siphon PG pedal ganglion

DD digestive duct PL palp

EG digestive diverticula PM pallial muscles

DH dorsal hood

ES exhalent siphon

FA feeding aperture

PP palp proboscis

PR_ pedal retractor muscle

PSA posterior sorting area

FM _ pedal muscles RM longitudinal muscle

FT foot SC _ statocyst

GC gland cells SE siphonal embayment

GD duct of gland SF sole of foot

GI gill SS _ style sac

GS gastric shield ST stomach

HG hind gut SY fold of sensory organ

HT heart TE tentacle

IF inner muscular fold T< transverse muscle

IS__ inhalent siphon TS tooth of gastric shield

LI ligament VG visceral ganglion

Family Nuculanidae Adams & Adams 1858

Shell elongate, usually moderately compressed, may be ros-

trate, shell gape if present, restricted to short posterior

margin where siphons protrude, concentric sculpture usually

present which may be strongly incised, middle and inner shell

layers non-nacrous; teeth chevron-shaped; ligament internal

or external with resilium; combined siphons present, usually

a simple siphonal tentacle attached to the left or right side of

the siphonal embayment.

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Subfamily Yoldiellinae Allen & Hannah 1986

Shell small, usually compressed, ovate or elongate subovate,

occasionally with ill-defined rostrum, not gaping, smooth, or

very fine concentric sculpture; ligament amphidetic, largely

internal; combined siphons with various degrees of tissue

fusion, siphonal embayment small; hind gut with various

configurations.

Genus Yoldiella Verrill & Bush 1897

TYPE SPECIES. By original designation, Yoldia lucida Lovén,

1846.

Shell small, fragile, usually slender, subovate, usually

glossy, no escutcheon or lunule, no carina, not gaping,

occasionally fine concentric sculpture, postero-ventral margin

may be slightly sinuate, postero-dorsal margin usually slightly

convex, maybe posteriorly angulate; umbo usually anterior

occasionally posterior or central; chevron-shaped hinge teeth

may or may not extend beyond the inner limit of adductor

muscles; no chondrophore; except for very small external

componant, ligament internal and amphidetic, but may

extend anteriorly and/or posteriorly to a small degree, hind-

gut with various configurations, mostly deep-water species

beyond shelf-slope break.

Note. A detailed account of an internal morphology is given under

Y. lata (p. 34).

Yoldiella lucida (Lovén 1846)

TYPE LOCALITY. Hammerfest, northern Norway (desig. A.

Warén, 1989).

TYPE SPECIMEN. Lectotype (desig. A. Warén, 1989), Swed-

ish Museum of Natural History, No. 1533.

Yoldia lucida Lovén 1846, p.34.

Fig. 1 Yoldiella lucida. Lateral views of

shells of different size seen from the

right side to show variation in shell

outline. Collected by R.V. Dana 1922; a

& b, 50°20'N 9°00’E, 350 m; c & d,

58°13'N, 9°34’E, 650 m. (Scale = 1.0

mm).

Leda lucida Jeffreys 1869, p. 173. pl.100, Fig. 1; Jeffreys

1879, p. 578;Locard 1898, p. 351, 362.

Portlandia lucida Sars G.O. 1878, p.37. pl. 4, Figs. 8a, 8b;

Norman 1893, p. 364; Posselt 1898, p. 36; Ockelmann

1958, 122, p. 29.

Yoldiella iris Verrill & Bush 1898, 20, p. 863-864, pl. 80. Fig.

1,2, pl. 82, Fig. 11; Type specimen U.S., Natl. Mus.

159722.

Yoldiella lucida Tebble 1966, p. 29, Fig. 156.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

NORWEGIAN BASIN

Thor 273 610

350 50 58°20'0N 09°00'0E

Dana 2896 60 58°13'0N = 09°34'0E

NORTH AMERICAN BASIN

Chain 58 105) 530; 1249 39°S6'6N') 71203'6W © ET (515166

Chain 88 207 805— 264 39°51’3W 70°S4'3W ES 21.2.69

811 — 39°51'0W =70°56'4W

WEST EUROPEAN BASIN

Incal DS03 609 2 S57°57'0N = 10°43'0W CP. 16.7.76

DS04 619 1 S7°58'0N 10°43'0W CP 16.7.76

Museum material examined is listed in the text.

Specimens of Yoldiella lucida have most subtle differences

in shape that taxed the descriptive powers of our predecessors

and as they do ours. Jeffreys (1879) recognized three varieties

(lucida, declivis and truncata) while Locard (1898), accepting

the form figured by Sars (1878) as the type, recognized five

varieties (truncata — the form figured by Jeffreys, intermedia,

minor, depressa, and ventricosa).

Three thousand miles to the west, and in the same year as

Locard, Verrill & Bush (1898) described what they thought to

be Y. lucida from the North West Atlantic and two closely

related north-east Atlantic species (Yoldiella iris and Yoldi-

ella inflata).

We have examined material from the Zoological Museum,

Copenhagen, specimens identified by Verrill & Bush, the

Jeffreys collections in London and Washington and Scandinavian

material from a variety of sources which includes specimens

identified by Dr. Kurt Ockelmann in his study of Greenland

material. To prevent even more confusion we accept as our

baseline that specimens from Eastern Arctic and northern

temperate shallow water populations of the east Atlantic adja-

cent to the type locality and which are described in the earliest

accounts, as Yoldiella lucida s.s. We have also examined West

Atlantic material some of which was misidentified and which we

recognize as Y. lucidas.s. namely:-

MCZ No. 137266 labelled Yoldiella inflata, S. Block

Island, 180— 190 m.

MCZ No. 227737 labelled Yoldiella lucida V & B, off

Bradlees Bank, 120 m.

MCZ No. 159722 (unlabelled).

MCZ No. 202847 (which includes specimens from a num-

ber of Stations mixed together).

MCZ No. 78292 labelled Sta. 2697, off Halifax N.S., 377

USNM No. 73172 labelled Y. lucida, 200 m.

USNM No. 202847 labelled Gulf of Maine. Mixture from

several stations.

Specimens misidentified as Y. iris in the U.S. National

Museum, but which are clearly Y. lucida s.s. :-

USNM No. 74517 labelled Gulf of Maine, 172 m.

USNM No. 159717 labelled Gulf of Maine, 40m.

USNM No. 159718 labelled Gulf of Maine, 134 m.

Samples of Y. Jucida from the Skaggerak, loaned by the

University Museum, Copenhagen, agree well with the figure

of Sars (1878) and which Locard (1898) considered as the

type (Fig. 1). These are also very similar to the shallow water,

North American specimens referred to as Y. lucida and Y. iris

by Verrill & Bush (1898). These latter specimens are very

slightly more inflated but otherwise identical to the specimens

taken from North American Basin Stations 105 and 207 (Figs.

4&7).

Thus, Y. lucida s.s. is found in Arctic and North Atlantic

waters at shelf and upper slope depths, including the northern

part of North America Basin, off Nova Scotia, Norwegian

Sea, Greenland, Iceland, Skagerak and West European

Basin. Depth range: 38-811 metres.

SHELL DESCRIPTION (Figs. 1-4 & 15, Table 1). Shell elon-

gate, ovate, moderately inflated, inequilateral, irregular con-

centric ridges, partially opaque, umbos moderately large,

inwardly directed, proximal dorsal margin close to umbos

depressed in many but not all specimens, antero-dorsal and

postero-dorsal margins raised to form sharp, low, keel on

either side of umbo, distally antero-dorsal margin extends in

almost straight line to point opposite anterior limit of hinge

plate then curves to the anterior margin, ventral margin long,

even curve, distal postero-dorsal margin slopes in almost

straight line, close to dorsal limit of posterior margin maybe

slightly upturned, limit of posterior margin supramedial,

slightly truncate, postero-ventral margin not sinuous, but

may be slightly flattened; hinge plate moderately broad,

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 2 Yoldiella lucida. Lateral views of shells from off the

northeast coast of America; a, USNM No. 73172, 200 m; b,

USNM No. 74517 labelled Yoldiella iris, Gulf of Maine, 172 m; c,

USNM No. 159717 labelled Yoldiella iris, 40 m. (Scale = 1.0

mm).

except where narrow below umbo, anterior plate elongate

extends opposite anterior margin of adductor muscle, poste-

rior plate relatively short, does not reach posterior margin of

posterior adductor muscle, hinge teeth chevron-shaped, mod-

erately stout, maximum of 14 recorded in each series, occa-

sionally anterior series has one more tooth than posterior;

ligament amphidetic, moderately elongate, anterior and pos-

terior lobes extend ventral to hinge plate.

The above description is of a fully grown animal. In smaller

Fig. 3 Yoldiella lucida. Outline drawings of shells from the right

side from Sta. 105 to show change in shape with increase in size.

(Scale = 1.0 mm).

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Fig. 4 Yoldiella lucida. Hinge plates of a, right valve of a specimen from Sta. 105 (North America Basin); b & c, right and left valve of

specimens from ‘Thor’ Sta. 28 to show variation in the shape of the ligament. (Scales = 0.5 mm).

specimens the antero-dorsal margin is more convex, the

postero-dorsal margin is normally angulate and the posterior

margin more rounded (Fig. 4). As in many species of

Yoldiella older specimens tend to become subrostrate.

Prodissoconch length: 198 4m. Maximum recorded shell

length: 6.9 mm.

INTERNAL MORPHOLOGY. (Figs. 5 & 6) The mantle margin

has a well-developed anterior sense organ. Posteriorly the

siphons are combined, the inhalent siphon being open ven-

trally. A well-developed feeding aperture lies immediately

ventral to the siphons with numerous gland cells present in

what is a broadened region of the inner muscular lobe. A long

siphonal tentacle originates usually on the left side of the

siphonal embayment near the base of the siphon. The adduc-

tor muscles are large and unequal in size. The posterior

muscle is oval in cross-section and between 1/2 and 1/3 the

size of the anterior which is more circular in section.

The visceral and cerebral ganglia are relatively large,

club-shaped, with an exceptionally thick connecting commis-

sure. The pedal ganglia are also large but more round in

outline, and each with a large statocyst dorsal to it. The foot

is anteriorly directed with well-developed pedal retractor

muscles. The byssal gland is moderate in size. The gills are

well-developed with between 16-23 gill filaments, the num-

ber depending on the size of the individual. Posteriorly the

gill axes attach to the junction between the two siphons. The

labial palps are moderately large extending approximately a

third across the body with between 13-23 palp ridges on the

inner face. The palp proboscides are well-developed and are

long and muscular. A wide ciliated oesophagus opens into a

large stomach, the dorsal hood of which lies close to the

dorsal margin of the body. There is a large style sac which

penetrates the lower posterior half of the foot. The hind gut

forms a single loop on the right side of the body. It has a

typhlosole along its entire length. There are two digestive

diverticula to the left and one on the right of the stomach.

Material similar to that present in the stomach was observed

in the left hand digestive diverticulum. The kidney is rela-

tively small in comparison with Yoldiella species from deeper

waters. The sexes are separate, and the gonads overlie the

viscera dorsally and laterally. 203 ova were present in a

specimen of 3.4 mm total length.

Yoldiella obesa obesa (Stimpson 1851)

TYPE LOCALITY. Original not known; Type locality here

designated, St. Georges Bank, U.S. Fish Comm. Sta. 2072,

2.10.1883, 43°53'N, 65°35'W, Beam Trawl, 858 fms.

TYPE SPECIMEN. Holotype believed lost in Chicago fire.

Neotype here selected, USNM No. 38419.

Leda obesa Stimpson 1851, p. 113; Stimpson 1851, p. 10, pt.

II, Fig. 1; Tryon 1873, p. 184, pl. 38, Figs. 500, 501.

16 J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 5 Yoldiella lucida. Lateral view of the internal morphology from the right side with detail of the posterior part of the mantle cavity and

the partially expanded siphon. (Scales = 0.5 mm).

Yoldia obesa Gould 1870, p. 155, Fig. 463; Verrill 1874, p. 46, Verrill 1874, p. 352, p. 368; Verrill 1874, p. 396.

p. 412, p.503; Smith & Harger 1874, p. 18, p. 23;

Yoldia lucida Verrill 1881, pl. XLIV, Fig. 1; Verrill 1884, p. 279

(in part); Verrill 1885, p. 576 (in part); Bush 1893, p. 233.

Yoldiella lucida Verrill & Bush 1897, p. 55. Fig. 14; Verrill &

Bush 1898, p. 861, 862, 863, pl. 77, Fig. 2, pl. 80, Fig. 3.

56!

MATERIAL.

Cruise Sta

Atlantis II 62

12 64

Chain 58 103

Atlantis II 128

30 131

Chain88 210

Fig. 6 Yoldiella lucida. External view of the stomach as seen from

a, antero-frontal; b, right lateral; c, left lateral aspects. (Scale =

0.5 mm).

Depth No

(m)

2496 6

2886 «8

2864 11

2033 28

1254 11

2178 51

2024- 11

2064

Lat

NORTH AMERICAN BASIN

36°26.0'N

38°46.0'N

38°16.0'N

39°43.6'N

39°46.5'N

39°38.5'N

= 39739 00N

39°43.0'N

— 39°43.2'N

Long

70°33.0'W

70°06.0'W

71°47.0'W

70°37.4'W

70°45.2’W

70°36.5'W

70°37.0'W

70°46.0'W

70°49.5'W

Yoldiella inflata Verrill & Bush 1897. p. 56. Figs. 3, 4. 11;

Verrill & Bush 1898, p. 864, 865, pl. 80, Fig. 8, pl. 82, Fig.

Gear Date

21. 8.64

24. 8.64

4. 5.66

16.12.66

18.12.66

22/

De 2269

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

WIL sone wie. bess | a

a mer isan s

Bae Ae opus “eae sae i ;

° Cin * a Oe

a e

e e fo)

. fe) .

3 4 5

Length (mm)

Fig. 7 Yoldiella lucida. Comparison of the shell proportions of three populations; small closed circles, Gulf of Maine USNM 202847; large

closed circles, a subsample from ‘Thor’ Sta. 28; open circles, a subsample from Sta. 105. H/L height/length, PL/TL postero-umbonal

length/total length, W/L width/length — all against length.

Also examined:

U.S. Fish Comm. USNM 73163 labelled Y. lucida (Lovén),

Cisco Bay 1873 m; Station 2072 USNM 38419 labelled

Yoldiella inflata (young), off Georges Bank 1569 m;

USNM 35189 labelled Yoldiella inflata off Georges Bank

2360 m.

Restricted to the North American Basin at lower slope

depths. Depth range 1254-2886 metres.

SHELL DESCRIPTION (Figs. 8-9 & 15). Shell moderately frag-

ile, elongate, ovate, with fine concentric ridges, inequilateral;

umbo moderately inflated, anterior, inwardly directed; dorsal

margin in the region of the umbos in all but a few specimens,

slightly concave, dorsal margins form sharp raised edge,

antero-dorsal margin smooth curve joining anterior margin

with no angulation, ventral margin smooth, relatively deep

curve, postero-dorsal margin in large specimens almost

straight, subangulate with posterior margin, extreme poste-

rior limit of shell dorsal to horizontal midline; hinge plate

moderately strong, parallel to margin, chevron-shaped teeth

fairly stout, anterior and posterior hinge plates with same

number of teeth, occasionally with one additional tooth on

posterior plate; ligament amphidetic, circular in lateral view,

extends ventral to hinge plate but without chondrophore,

short anterior and posterior secondary external periostracal

extensions.

Prodissoconch length: 215 4m. Maximum recorded shell

length: 4.45 mm.

oy |

Fig. 8 Yoldiella obesa obesa. Neotype: USNM No. 38419. Lateral

view of a right valve and a hinge plate of left valve, also a dorsal

view of the umbos showing the outline of the prodissoconch.

(Scale = 1.0 mm).

18 J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Table 1 Yoldiella lucida; numbers of anterior and posterior hinge teeth in specimens from different localities.

Biscay North Atlantic ‘Thor’ N. European

Length Teeth No. USNM. Length Teeth No. Length Teeth No.

(mm) Ant. Post. No. (mm) Ant. Post (mm) Ant. Post.

INCAL DS 02 2.28 6 6 738419 3.07 8 8 2.50 8 7

INCAL DS 01 2.42 7 7 159718 3.22 10 10 PEI] 8 9

INCAL DS 01 ATS) 7 7 74517 8)-8)5) 11 10 POI 9 5

INCAL DS 01 2.95 8 8 202847 3.84 11 11 3.44 9 9

INCAL CP 01 3.24 9 9 202847 3.94 11 11 3.49 9 10

INCAL DS 01 3.28 8 8 202847 4.03 11 10 4.31 11 11

INCAL CP 01 3.49 8 8 202847 4.51 12 12 4.39 12 12

INCAL DS 02 3.57 9 9 202847 4.67 11 11 4.67 11 11

POLYGAS

DS 26 3.61 11 11 IBN 4.93 12 12 5.02 11 12

INCAL DS 01 SH, 10 10 202847 5.98 12 14 5.02 14 14

INCAL DS 01 4.31 10 10 202847 6.02 15 14 5.10 13 14

5.10 11 12

5.10 13 13

S18) 12 11

5.61 13 13

Very similar to Y. lucida (for points of difference see

p. 19), past records e.g. (Verrill & Bush, 1898; Warén, 1989)

testify to this.

also well-developed and provided with numerous gland cells.

The broad and, in preserved specimens, convoluted part of

the inner muscular lobe which forms the feeding aperture,

y ; extends anteriorly beyond the limit of the aperture and is

INTERNAL MORPHOLOGY (Fig. 10). The internal morphology

is similar to that of Y. lucida. There is a well-developed

ciliated anterior mantle sense organ. The inhalent and exhal-

ent siphons are combined for most of their length, and the

inhalent siphon is not fused along its ventral margin. The

siphonal tentacle is well-developed and usually attached to

the left of the base of the siphons. The feeding aperture is

Fig. 9 Yoldiella obesa obesa. Lateral views of shells from the right

side to show change in shape with increasing size and detail of

hinge plate. Specimens from Sta. 62 North America Basin. Note

adductor muscles and hind gut loop seen through the transparent

shell. (Scale = 1.0 mm).

Fig. 10 Yoldiella obesa obesa. Lateral views of the internal

morphology from right and left side. (Scale = 1.0 mm).

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

heavily ciliated throughout. The adductor muscles are rela-

tively large and unequal in size. The posterior muscle is oval

in outline and is approximately 1/2 to 1/3 the size of the

anterior muscle.

The gills are well-developed with up to 16 gill filaments

depending on the size of the individual. The number of ridges

on the inner surface of the labial palp varies between 12-17.

The palps extend over approximately half the body width and

have long, moderately thick palp proboscides. The visceral

and cerebral ganglia are elongate and each large pedal

ganglia has a large statocyst dorsal to it. The foot is large and

directed anteriorly, with well-developed retractor muscles.

There is a moderately large byssal gland in the heel. The

oesphagus is wide and opens into a voluminous stomach. The

style sac penetrates into the lower portion of the foot. The

hind gut forms a single loop on the right side of the body and

has a typhlosole along its entire length. The digestive diver-

ticula, as in other species, are situated one to the right and

two to the left of the stomach. The ducts to the left hand

diverticula enter the stomach close together, ventral to the

gastric shield one posterior to the other. The kidney is small.

Gonads overlie the lateral and dorsal sides of the viscera and

the sexes are separate.

Y. obesa s.s. and Y. lucida differ as follows:- (1) The

ventral margin of Y. obesa is slightly deeper and more

rounded. (2) The anterior adductor of Y. obesa is relatively

smaller when compared with a specimen of Y. lucida the

same size. (3) The internal ligament of Y. obesa is smaller,

shorter and more rounded. (4) The umbo is more anterior in

Y. obesa and slightly larger and more prominent. (5) The

posterior margin is more rostrate and tapered in Y. obesa and

Fig. 11 Yoldiella obesa incala. Lateral view of shells from the right

side to show change in shape with increasing size, and detail of

the hinge plate of a right valve. Specimens from Incal Sta. DS02.

(Scales = 1.0 mm).

less truncate. (6) The posterior section of the loop of the hind

gut is less curved and almost vertical in Y. obesa.

Yoldiella obesa incala (new subspecies)

TYPE LOCALITY. R.V. Jean Charcot, Cruise INCAL, Sta.

DS01, East of Rockall Island, 15.7.1976, 57°59’N, 10°40’W,

Epibenthic Trawl, 2091 m.

TYPE SPECIMEN. Holotype: Museum National d’Histoire

Naturelle, Paris, Paratypes: in collection held by J.A. Allen.

MATERIAL.

Cruise Sta’ Depth No Lat Long Gear Date

(m)

WEST EUROPEAN BASIN

Jean Charcot DS25 2096 3 44°08.2'N 4°15.7';W DS 1.11.71

(Polygas) DS26 2076 3 44°08.2'N 4°15.0'W DS _ 1.11.71

Jean Charcot DS51 2430 1 44°11.3'N 4°15.4;W DS 12. 2.74

(Biogas IV)

(Biogas V) CPO07 2170 4 44°09.8'N 4°16.4°;W CP 21. 6.74

(Biogas VI) DS80 4120 2 46°29.5'N 10°29.5'W DS _ 27.10.74

DS86 1950 7 44°04.8'N 4°18.77;W DS_ 31.10.74

DS87 1913 5 44°05.2'N 4°19.4;W DS _— 1.11.74

(Incal) DSO1 2091 518 57°59.0'N 10°40.0'W DS _ 15. 7.76

DS02 2081 452 57°58.0'N 10°49.0'W DS _ 16. 7.76

CP01 2068—- 35 57°57.0'N 10°43.0'W CP 16. 7.76

2040

CP02 2091 3 57°58.0'N 10°43.0'W CP 16. 7.76

Restricted to the West European Basin at lower slope depths.

Depth range: 1913-2170 mm.

SHELL DESCRIPTION (Figs. 11 & 12). Y. obesa incala is similar

to Y. obesa s.s. and requires little description other than to

identify points of differences with the North American sub-

species.

W/L : agen

e 5

‘80

Me | ee AS og Te)

Length(mm)

Fig. 12 Yoldiella obesa incala. Variation in the ratios of height

H/L, width W/L and postero-umbonal length PL/TL to length

against length of a sample from Incal Sta. CP01 from the Bay of

Biscay.

The subspecies has been long confused with Y. lucida s.s.

(Warén, 1989) and there is little doubt that records of the

latter species from deeper than 1000 m are of Y. obesa incala.

In large specimens in particular, elongation and narrowing of

the posterior margin together with a slightly upturned distal

end of the postero-dorsal margin, resembles Y. lucida. A

population from Rockall although similar in outline is rela-

tively smaller and less inflated than the Biscay populations.

Prodissoconch length: 187-208 »m. Maximum recorded

shell length: 4.8 mm.

INTERNAL MORPHOLOGY. Mantle structures are similar to

those in Y. obesa s.s., for example the ventral margin of the

inhalent siphon is open ventrally, however the feeding aper-

ture is not particularly well-developed. The posterior adduc-

tor muscle is oval in shape and half the size of the crescent-

shaped anterior muscle. There is a large stomach and style

sac, and a single loop of the hind gut on the right side of the

body. The byssus gland is moderately small. The palp probos-

cides are long and palp ridges number up to 21. The gills are

well-developed with up to 17 plates present.

Points of distinction are as follows:- (1) The umbo in Y.

obesa incala is slightly more medial than in Y. obesa s.s. (2)

The posterior dorsal section of the hind gut loop takes a

slightly more anterior course than in Y. obesa s.s. (3) The

anterior adductor is relatively more ventral in position than in

Y. obesa s.s. (4) Although the ligament is relatively short

and, in many specimens rounded as it is in the North

American subspecies, in some specimens the anterior and

posterior ends are slightly swollen giving a ‘dumb bell’

appearance.

In a specimen 3.03 mm length, 281 ova were counted, with

a maximum diameter 119 jm. In two specimens less mature,

240 and 387 ova were present in animals measuring 3.06 mm

and 4.23 mm respectively.

Fig. 13 Yoldiella similirus. Lateral views of shells from the right

side and a hinge plate of a left valve. Specimens from Sta. 236

Argentine Basin. (Scale = 1.0 mm).

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Yoldiella similiris (new species)

TYPE LOCALITY. R.V. Atlantis II, Cruise 60. Sta. 236,

Argentine Basin, 11.3.1971, 36°27.0’S, 53°31.0’W-36°28.1'S,

53°32.3'W, Epibenthic Trawl, 409-518 m.

TYPE SPECIMEN. Holotype: BM(NH) 1992028. Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta. Depth No Lat Long Gear Date

(m)

ARGENTINE BASIN

AtlantisII 236 409- 86 36°27.0'S 53°31.0'W ES 11.3.71

60 518 = 36°28.1"S 53°32.3'W

237 993> ~"S13673226'S” "532230 Welles a7

1011

Restricted to shallow slope depths in the Argentine Basin.

Depth range: 497-1011 metres.

SHELL DESCRIPTION (Figs. 13, 15-17). Shell small, subovate,

moderately inflated, smooth, fine irregular concentric lines,

inequilateral; umbos small, anterior of midline, inwardly

directed; antero-dorsal margin convex, curves evenly to ante-

rior margin, ventral margin convexity increases slightly poste-

riorly, posterior margin obliquely subtruncate, postero-dorsal

margin approximately straight, gently sloping, posteriorly

forming a blunt angle, dorsal margins on either side of umbo

form an acute edge; hinge plate well-developed, anterior

slightly arched, posterior almost straight, 11 anterior and 12

posterior strong angular teeth in individual 3.75 mm long;

ligament amphidetic, small secondary external periostracal

extensions on either side of umbo, internal primary ligament

moderately large, extends below hinge line.

Prodissoconch length: 198 1m. Maximum recorded shell

length: 3.75 mm.

The shell and internal morphology of Y. similiris is very

similar to that of Y. lucida s.s. The following differences are

noted:- The umbo of Y. similiris is slightly more anterior, this

Fig. 14 Yoldiella similiris. Lateral view of internal morphology

from the right side. (Scale = 1.0 mm). For identification of parts

see Fig. 5.

DEEP-SEA PROTOBRANCHIA (BIVALVIA) 21

Fig. 15 Yoldiella spp. Dorsal

views of shells of a, Y. obesa

obesa; b, Y. similiris and c, Y.

lucida. (Scale = 1.0 mm).

is particularly noticeable in the larger specimens. The height

to length ratio is greater in Y. similiris.

INTERNAL MORPHOLOGY (Fig. 14). The internal morphology

is very similar to that of Y. lucida. The adductor muscles are

unequal in size, the posterior muscle is oval and approxi-

mately 1/3 the size of the anterior. There are a smaller

number of gill filaments (maximum of 11 observed) and the

labial palp ridges vary between 11-13. The stomach and style

sac appear relatively smaller than those in Y. /ucida and the

hind gut, while making a single loop on the right side of the

body, is not as deep as it is in the latter species. A maturing

female (3.4 mm total length) had 203 ova with a maximum

WL: .' ib ayer eerie Seeing

H/L < Cee oe °

ee Length (mm)

Fig. 16 Yoldiella similiris. Lateral views of a series of shells to bs ; serie sabe ai " :

Bio eoabec in chips witht ecawth, Specinucne tomlStal 256 F ig. 17 Yoldiella similiris. Variation in the ratios of height HI/L,

. ; width W/L and postero-umbonal length to length against length of

cone bast, (Seale Sa: HD): a subsample from Sta. 236. Argentine Basin.

diameter of 83 wm (probably less than half their eventual

maximum size).

Yoldiella hanna (new species)

TYPE LOCALITY. R.V. Atlantis II Cruise 42, Sta. 186, Cape

Basin, 15.5.1968, 22°57’S, 13°05’E, Epibenthic Trawl,

439-481 m.

TYPE SPECIMEN. Holotype BM(NH) 1992022, Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

CAPE BASIN

AtlantisII 186 439- 21 22°57.0’'S 13°05.0'E ES 16.5.68

42 481

188 619% 7 23°00.0’'S 12°58.0’'E ES 16.5.68

622

The species is restricted to the upper slope in the Cape Basin.

Depth range: 439-622 metres.

SHELL DESCRIPTION (Fig. 18). Shell small, ovate, relatively

inflated, inequilateral (posterior umbonal length 52-57% of the

total length), sculpture, fine concentric lines at ventral margin,

pale straw-coloured periostracum; umbos slightly raised,

inwardly directed; dorsal margin slightly convex, antero-dorsal

Fig. 18 Yoldiella hanna. Lateral views from the right side of three

shells and an internal view of a right valve to show detail of the

hinge plate. Specimens from Sta. 186 Cape Basin. (Scale = 1.0

mm).

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 19 Yoldiella hanna. Lateral view from right side of the

internal morphology. Specimen from Sta. 186 Cape Basin. (Scale

= 1.0 mm). For identification of parts see Fig. 5.

margin slopes gradually and smoothly to anterior margin, dorsal

part of which more convex, ventral margin long, smooth, curve,

postero-dorsal margin almost straight maybe slightly concave,

slopes gently to blunt-angled supramedial posterior margin;

hinge plate very strong, wide, except centrally under umbo; 10

strong chevron-shaped teeth on each side of ligament in largest

specimen; ligament amphidetic, goblet-shaped, extends below

margin of hinge plate.

Prodissoconch length: 200 1m. Maximum recorded shell

length: 3.2 mm.

INTERNAL MORPHOLOGY (Fig. 19). Well-developed combined

siphons are present with a well-developed feeding aperture

ventral to them. The siphonal tentacle lies to the left. The

posterior adductor muscle is very small and elongate oval in

cross-section. The anterior adductor muscle is crescent-shaped

60 e

Length (mm)

Fig. 20 Yoldiella spp. Comparison of the shell proportions of Y.

hanna (closed circles) and Y. artipica (open circles). Height H/L,

width W/L and postero-umbonal length PL/TL to length against

length.

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

and at least three times as large as the posterior. The foot is

large, anteriorly directed and with a large byssal gland. The

cerebral and visceral ganglia are relatively large, club-shaped

with a stout commissure. The pedal ganglia are also large but

more rounded. The labial palps are well-developed and extend

across approximately half of the body and have up to 14 broad

internal ridges present on their inner face. The palp proboscides

are moderately long. The gills are small with up to 18 alternating

filaments.

The stomach is large and laterally distended. The proximal

part of the hind gut penetrates deep into the foot, ventral to

the pedal ganglia. It forms a single loop on the right side of

the body.

In external appearance the shells of the species can be

easily confused with Yoldiella artipica (p. 25) although Y.

hanna is slightly more inflated and the height/length ratio is

slightly greater (Fig. 20). Nevertheless, hinge and teeth differ

markedly, as does the hind gut configuration.

Yoldiella capensis (new species)

TYPE LOCALITY. R.V. Atlantis II, Cruise 42, Sta. 189, Cape

Basin, 15.5.1968, 23°00’S, 12°45’E, Epibenthic Trawl,

1007-1014 m.

TYPE SPECIMEN. Holotype BM(NH) 1992026, Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta. Depth No Lat Long Gear Date

(m)

CAPE BASIN

Atlantis] 188 619 70 23°00.0'S 12°58.0'E ES 16.5.68

42 622

189 =1007— 918 23°00.0’'S 12°45.0'E ES _ 15.5.68

1014

190 974- 15 23°05.0'S 12°45.0'E AD 17.5.68

979

Only found at slope depths of the Cape Basin. Depth range:

619-1014 m.

SHELL DESCRIPTION (Figs. 21 & 22). Shell, subovate, moder-

ately inflated, inequilateral, posteriorly somewhat wedge-

shaped, smooth with a few fine concentric lines, periostracum

pale straw-coloured; umbos slightly raised, inwardly directed;

antero-dorsal margin convex, slopes steeply from umbo to

anterior margin, dorsally posterior margin produced into

rounded point, postero-dorsal margin long, varying from

slightly convex in smaller specimens (usually) to slightly

concave, slopes gradually to posterior margin, hinge plate

strong, relatively long, plates approach shell margin below

umbo, anterior plate arched with up to 9 erect chevron teeth,

posterior plate extends to anterior margin of adductor,

straighter than anterior, with up to 11 teeth and does not

extend beyond posterior margin of adductor; ligament

amphidetic, bilobed in lateral view, extends below hinge line.

Prodissoconch length: 170 1m. Maximum recorded shell

length: 8.0 mm.

With increasing size this species becomes more posteriorly

elongate and the distal posterior dorsal limit more pointed

(Figs. 21 & 22). Furthermore the posterior dorsal margin

becomes less curved with increasing size, so much so that

Fig. 21 Yoldiella capensis. Lateral view from the left side of the

largest shell taken from Sta. 189 Cape Basin and hinge detail of

right valve of the same specimen. (Scale = 1.0 mm).

Fig. 22 Yoldiella capensis. Lateral views of shells from the right

side to show change in shape with growth. Specimens from Sta.

188 Cape Basin. (Scale = 1.0 mm).

without a size series it would be difficult to equate small

specimens with large. Other shell ratios (H/L and W/L)

remain more or less constant as length increases (Fig. 23).

INTERNAL MORPHOLOGY (Fig. 24). Specialization of the

mantle includes a well-developed anterior sense organ and

combined exhalent and inhalent siphons. The latter are

well-developed with thick muscular walls. A siphonal tentacle

lies to the left of the siphons. There is a feeding aperture

ventral to the siphons which is much folded in the contracted

state. The adductor muscles are relatively small. The poste-

rior muscle is narrow and elongate, while the anterior is 2 to 3

times larger and crescent-shaped.

The gills are well-developed with up to 20 plates. The labial

palps are moderate in size. They extend between 1/4 — 1/3

distance across the body and have long and slender palp

proboscides. The nervous system is well developed with large

club-shaped visceral and cerebral ganglia and massive com-

missures which link them. Large, round, pedal ganglia each

have a large statocyst full of refractile granules dorsal to

W/L

1 2 3

Length(mm)

Fig. 23 Yoldiella capensis. Variation in the ratios of height H/L,

widthW/L, and postero-umbonal length PL/TL to length against

length of a subsample of specimens from Sta. 188 Cape Basin.

Fig. 24 Yoldiella capensis. Lateral view from the right side of the

internal morphology. Specimen from Sta. 188, Cape Basin. (Scale

= 1.0 mm). For identification of the parts see Fig. 5.

them. The foot is large, well-developed with an anteriorly

directed attitude. The stomach and style sac are also large.

The hind gut forms a single loop on the right side of the body.

This species bears some resemblance to Yoldiella lucida and

to Y. bilanta (Fig. 137).

Yoldiella bilanta (new species)

TYPE LOCALITY. R.V. Atlantis II, Cruise 42, Sta. 192, Cape

Basin, 17.5.1968, 23°05.0’S, 12°31.5'E, Epibenthic Trawl,

2117-2154 m.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

‘TYPE SPECIMEN. Holotype: BM(NH) 1992027, Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta’ Depth No Lat Long Gear Date

(m)

CAPE VERDE BASIN

AtlantisII 138 1944- 1 10°36.0’N 17°52.0'W ES 4.2.67

31 1976

141 2131 210730:05N, 1725 SOW See: 207,

142 1624— 1 103220) Nev 17 51S WES 2267,

1796

144 2051-22 :10°36.0'N 17°49.0'W ES _ 5.2.67

2357

CAPE BASIN

AtlantisII 191 1546- 1025 23°05.3'S 12°31.5'E ES 17.5.68

42 1559

192 2117— 1697 23502:0'S, _ 12°19.04E WES) 1755168

2154

Found in the Cape Verde and Cape Basins at lower slope

depths. Depth range: 1446-2357 metres.

SHELL DESCRIPTION (Fig. 25). Shell slender, elongate ovate,

inequilateral, smooth with few fine concentric lines, perios-

tracum pale straw-coloured; umbos anterior to midline,

slightly inflated, orthogyrate; antero-dorsal margin moderat-

ley convex, curves evenly to anterior margin, ventral margin

long, smooth curve, anterior curvature slightly more convex

than posterior, posterior margin narrow, slightly produced

with supramedial rounded angle, postero-dorsal margin

slopes gradually more or less straight or slightly concave from

umbo to posterior limit of hinge plate, then more acutely to

posterior margin; hinge plate, strong, long, relatively narrow

and straight with 9 anterior and 10 posterior teeth in largest

specimen; anterior and posterior plates approach margin

below umbo; ligament amphidetic, bilobed goblet-shaped,

extends below hinge line, short anterior and posterior exter-

nal extensions of fused periostracum.

Prodissoconch length c 190 jm: Maximum recorded shell

length: 8.0 mm.

The morphology of the shell is similar to that of Yoldiella

capensis (Fig. 21). With increasing size the shell becomes

more posteriorly elongate and the postero-dorsal margin

becomes more straight so that the slight angulation at the

level of the limit of the posterior hinge margin becomes much

less obvious (Figs. 25 & 26). There is little change with

growth in the height and length and width to length ratios.

The hinge plate is more narrow and teeth less robust than in

Y. capensis and the lateral ‘dumb bell’ outline of the ligament

is very different from the more rectangular and deeper

ligament of the latter species.

INTERNAL MORPHOLOGY (Fig. 27). The most conspicuous

difference from Y. capensis is the size and shape of the

adductor muscles which are larger and more rounded in

Yoldiella bilanta The labial palps are relatively small and

extend approximately 1/3 distance across body. They bear up

to 16 palp ridges. The gill plates are relatively narrow and

number up to 18. The single loop of the hind gut has a greater

diameter but is not as ventrally deep as that in Yoldiella

capensis. Similar features to Yoldiella capensis include well-

developed combined siphons, nervous system, and a large,

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

W/L

Jove whed ae ae

meee es tte ae ong) ig agile

1 2 3

Length(mm)

anteriorly dirécted foot. The lateral papillae of the foot are

not so well-developed as those in Y. capensis.

The specimens from the Cape Verde Basin are somewhat

smaller and have a slightly deeper shell than those from the

Cape Basin. There appear also slight differences in the size of

the posterior adductor muscle and the gills, but these may be

a result of distortion following preservation. Such small

differences are within the normal variation of yoldiellid

species and at most represent a population difference.

Yoldiella artipica (new species)

TYPE LOCALITY. R.V. Atlantis II, Cruise 42, Sta. 200,

Angola Basin, 22.5.1968, 9°43.5'S, 10°57'0E — 9°41.0’S —

10°55.0’E, Epibenthic Dredge, 2644-2754 m.

Fig. 25 Yoldiella bilanta. Lateral views

of three shells from the right side and

internal view of a left valve to show the

hinge-plate. Specimens from Sta. 192

Cape Basin. (Scale = 1.0 mm).

Fig. 26 Yoldiella bilanta. Variation in

the ratios of height H/L, width W/L,

and postero-umbonal length PL/TL to

length against length of samples from

Sta. 191 (open triangles) and Sta. 192

(closed circles) Cape Basin.

TYPE SPECIMEN. : Holotype: BM(NH) 1992021, Paratypes:

in collection held by J.A. Allen.

MATERIAL.

Cruise Sta. Depth No Lat Long Gear Date

(m)

ANGOLA BASIN

Atlantis1IT 200 2644- 25 9°43.5’S LOPS 7-00 E ES 922-5268

42 2754 — 9°41.0'S 10°55.0'E

Walda DS20 2514 2 2°32.0'S S18 1VE ES ——71

Restricted to the abyssal rise of the south east Atlantic.

Depth range: 2514-2754 m.

Fig. 27 Yoldiella bilanta. Lateral view of the internal morphology

from the right side of a specimen from Sta. 192 Cape Basin.

(Scale 1.0 mm). For identification of parts see Fig. 5.

SHELL DESCRIPTION (Fig. 28). Shell small, ovate, not

inflated, inequilateral (posterior umbonal length 54-58% of

total length), in larger specimens antero-ventrally, very fine

concentric lines form broadly spaced ridges, periostracum

pale yellow, umbo slightly raised, inwardly directed; dorsal

margin slightly convex, antero-dorsal margin curves moder-

ately steeply and evenly with anterior margin, ventral margin

smooth curve, postero-dorsal margin slopes gently from

umbo to extended posterior margin; ligament amphidetic,

small, rounded, not extending below hinge plate, with small

secondary anterior and posterior external extensions of fused

periostracum ; hinge plate moderately long, relatively nar-

row, small chevron-shaped teeth, 7 anterior and 8 posterior.

Prodissoconch length: 200 ~m. Maximum recorded shell

length: 2.78 mm.

Shell measurements (mm) & ratios are as follows:-

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Length Height Width H/L W/L PET

2.00 1.46 - 0.73 - 0.54

2.69 1.89 = 0.70 - 0.56

2.78 1.98 - 0.71 - 0.58

1.64 113 0.53 0.69 0.33 0.54

2.23 JES 0.84 0.70 0.38 0.57

2.60 1.80 1.01 0.69 0.38 0.55

DDD, 1.76 1.01 0.70 0.40 0.57

PL = postumbonal length

INTERNAL MORPHOLOGY (Fig. 29). The combined exhalent

and inhalent siphons are large. The inhalent is somewhat

shorter than the exhalent and open ventrally. A large sipho-

nal tentacle originates on the left side of the siphonal embay-

ment close to the base of the siphon. The feeding aperture is

not particularly well-developed. There is a large anterior

sense organ. The posterior adductor muscle is long and

narrow, and only half the size of the bean-shaped anterior

muscle. The gills are well-developed with up to 20 gill plates.

The labial palps are relatively small with up to 12 internal

palp ridges with long, thin palp proboscides. The foot is

extremely long and slender with an extended sole fringed

with deep papillae. There is a large byssal gland in the heel

with large pedal ganglia dorsal to it. The visceral and cerebral

ganglia are of moderate size and club-shaped. The hind gut is

similar to that in Yoldiella lata (p. 32) with one complete turn

of a double loop to the right side. That in Y. artipica entends

further posteriorly than that in Y. lata. As in many yoldiellid

species the body wall enclosing the hind gut loops overhangs

the palps on the right side (Fig. 29).

Yoldiella similis (new species)

TYPE LOCALITY. R.V. Atlantis II, Cruise 42, Sta. 197,

Angola Basin, 21.5.1968, 10°24’S, 9°09’E — 10°29’S, 9°04’E,

Epibenthic Trawl, 4559-4566 m.

Fig. 28 Yoldiella artipica. A dorsal and two right

lateral views of shells, and one lateral view of a left

valve to show detail of hinge-plate. Specimens from Sta.

200 Angola Basin. (Scale = 1.0 mm).

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Fig. 29 Yoldiella artipica. Lateral view from the right side of the

interal morphology of a specimen from Sta. 200 Angola Basin.

(Scale = 1.0 mm). For identification of parts see Fig. 5.

TYPE SPECIMEN. Holotype: BM(NH) 1992023, Paratypes: in

collection held by J.A. Allen.

MATERIAL

Cruise Sta. Depth No Lat Long Gear Date

(m)

ANGOLA BASIN

AtlantisI] 196 4612- 1 10°19.0'S 9°04.0'E ES 21.5.68

42 4630

197) 4596, 35°) 10729015 S°04'0"E ~~ ES 9215.68

198 4559- 12 10°24.0'S 9°09.0°E ES 21.5.68

4566 — 10°29.0'S 9°04.0’E

Found at abyssal depths in the Angola Basin. Depth range:

4559-4630 m.

SHELL DESCRIPTION (Fig. 30). Shell small, ovate, very

slightly inflated, inequilateral with posterior margin suprame-

dially subrostrate, shell with very fine concentric lines, form-

ing ridging on ventral half of shell; periostracum pale yellow;

umbos slightly raised, internally directed; dorsal margin

slightly convex, antero-dorsal margin slopes from umbo to

form even curve with anterior margin, ventral margin

smoothly curved, posterior margin sharply curved where it

meets postero-dorsal margin; hinge strong, moderately

broad, extends to anterior and posterior limits of the anterior

and posterior adductors respectively; hinge teeth well-

developed, equal numbers (maximum 9) on anterior and

posterior hinge plates, ligament amphidetic, moderately

large, goblet-shaped with very small external extensions.

Prodissoconch length: 173 ~m. Maximum recorded shell

length: 2.92 mm.

The shell outline of this species is similar to that of

specimens of Y. jeffreysi from the Cape Verde Basin. The two

species can be distinguished by the larger ligament, broader

hinge and more rostrate posterior margin of Y. similis.

Fig. 30

a hinge-plate of a left valve compared with the hinge-plate of a

specimen of Y. jeffreysi (a) Specimens from Sta. 197, Angola

Basin and Sta. 316, West European Basin, respectively. (Scale =

1.0 mm).

Yoldiella similis. Lateral view of a shell from right side and

Shell measurements (mm) and ratios are as follows:-

Length Height Width H/L W/L Plenile

1.0 0.71 0.78 0.71 0.38 0.42

1.93 1.39 0.80 0.72 0.41 0.50

1.72 1.43 0.80 0.83 0.46 0.54

2.90 2.06 1:39 0.71 0.48 0.55

PL = postumbonal length

INTERNAL MORPHOLOGY (Fig. 31). The internal morphology

of Y. similis is very similar to that of Y. jeffreysi. The exhalent

siphon is combined with the less well-developed inhalent

siphon. The adductor muscles are unequal in size, the ante-

rior being approximately three times larger than the poste-

rior. In lateral view the posterior adductor muscle is oval in

outline while the anterior is ‘bean-shaped’. The foot has a

long, extended, narrow sole with a large byssal gland in the

heel. The nervous system is extremely well-developed with

large visceral and cerebral ganglia with short stout commis-

sures joining them. Gills appear to have relatively few plates

(up to 10) and the number of palp ridges is also few (up to 12)

but the latter are relatively broad. This species has a large

stomach and the hind gut makes one complete double coil to

the right side of the body.

Yoldiella sinuosa (new species)

TYPE LOCALITY. R.V. Knorr, Cruise 25, Sta. 299, Surinam

Basin, 29.2.1972, 7°55.1'N, 55°42.0'W, Epibenthic Trawl,

1942-2076 m.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 31 Yoldiella similis. Lateral view from the right side of the

internal morphology of a specimen from Sta. 197. Angola Basin.

(Scale = 1.0 mm). For identification of parts see Fig. 5.

TYPE SPECIMEN. Holotype: BM(NH) 1992025, Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta. Depth No Lat Long Gear Date

(m)

SURINAM BASIN

Knorr 25 299 1942—- 54 7°55.1'N 55°42.0'W ES 29.2.72

2076

Restricted to one Station on the lower slope of the Surinam

Basin. Depth range: 1942-2076 m.

SHELL DESCRIPTION (Figs. 32 & 33). Shell small, ovate,

moderately inflated, slightly inequilateral, surface smooth in

small individuals, ridges on ventral half of shell of larger

specimens, periostracum pale yellow; umbo small, slightly

raised, internally directed; no lunule or escutcheon; dorsal

margin convex, anterior and posterior margins slope at

similar angle from umbo, anterior margin smooth curve,

posterior margin slight extended and slightly subrostrate,

postero-dorsal margin slightly angled at posterior limit of

hinge plate, postero-ventral margin sinuous, ventral margin

slightly more convex posteriorly; hinge plate strong, rela-

tively long, with up to 9 anterior and 10 posterior chevron-

shaped teeth, hinge plate narrow below umbo; ligament

amphidetic, internal, ‘goblet-shaped’.

With increasing shell length, there is little change in the

height to length ratio but there is a slight increase in the width

to length ratio. There is also gradual post-umbonal extension

with the sinuous nature of the postero-ventral margin becom-

ing more conspicuous (Fig. 35).

Prodissoconch length: 179 wm. Maximum recorded shell

length: 3.69 mm.

INTERNAL MORPHOLOGY (Fig. 34). The combined siphons,

the siphonal tentacle (usually on the left side), and the

anterior sense organ are as in Y. similis. The adductor

Fig. 32 Yoldiella sinuosa. Lateral view of a shell from the right

side and detail of the hinge-plate of a right valve. Specimens from

Sta. 299 Guyana Basin. (Scale = 1.0 mm).

Fig. 33 Yoldiella sinuosa. Outline drawings of shells of different

sizes from the right side to show change in shape with growth.

Specimens from Sta. 299 Guyana Basin. (Scale = 1.0 mm).

muscles are approximately oval, the anterior muscle being

the larger and being almost twice the size of the posterior.

The gills have up to 17 plates. The labial palps are moderate

in size and extend 1/3 way across the body. They have up to

15 moderately broad ridges and each bears a long palp

proboscis. The pedal ganglia are large, round, with large

statocysts dorsal to them. The cerebral ganglia are slightly

larger than the visceral, both are club-shaped and well-

developed. The foot is large with a large byssal gland. The

stomach is large with a small, narrow style sac. The hind gut

takes an ‘S-shape’ course to the right side of the body before

returning to the mid dorsal margin and thence to the anus.

There is a fine typhlosole present along the length of the hind

gut. Ingested material was seen in part of the left digestive

diverticulum. The kidney is well-developed, extending anteri-

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

LI ST

orly on either side of the stomach, anterior to the lateral

pedal retractor muscles. It also pentrates the foot posterior to

the stomach.

Only male specimens were observed in which the testes

were restricted to the anterior dorsal and ventral limits of the

viscera.

Yoldiella sinuosa is characterized by its slightly sinuous

postero-ventral shell margin and the s-shaped course of the

hind gut (see p. ).

Yoldiella blanda (new species)

TYPE LOCALITY. R.V. Atlantis II, Cruise 60, Sta. 247,

Argentine Basin, 17.3.1971, 43°32.0'S, 48°58.1'W,

Epibenthic Trawl, 5208-5223 m.

TYPE SPECIMEN. Holotype: BM(HM) 1992020, Paratypes: in

a collection held by J.A. Allen.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

ARGENTINE BASIN

AtlantisIT 242 4382— 119 38°16.9'S 51°S6.1’E ES 13.3.71

60 4402

245 2707 imsO9.47S, 53 011'E. ES 143571

247 5208- 106 43°33.0'S 48°58.1’E ES 17.3.71

5523

252 4435 42 38°29.8'S

256 3906—- 63 52°19.3’S

3117

259 3305— 20 37°13.3'S

3317

5209 EES 92273.71

2g IS Ee ES 2453771

52°45.0'E ES 26.3.71

This species is restricted to abyssal depths in Argentine

Basin. Depth range: 2707-5223 m.

SHELL DESCRIPTION (Figs. 36 & 37). Shell ovate, laterally

Fig. 34 Yoldiella sinuosa. Lateral view

from the right side of the internal

morphology of a specimen from Sta. 299

Guyana Basin. (Scale = 1.0 mm).

WL :

» “ =

e ° @

HL . x

70 e % ? e

\PL/TL e

e e e

7) lian haar wa We Mlle? - > ae ee

1 2 3 4

Length(mm)

Fig. 35 Yoldiella sinuosa. Variation in the ratios of height H/L,

width W/L, and post-umbonal length PL/TL to length against

length of a subsample from Sta. 299 Guyana Basin.

compressed, fragile, slightly inequilaterial; umbos small, not

markedly raised or inflated, slightly anterior to the mid line;

antero-dorsal, anterior and ventral margins, evenly curved,

postero-dorsal margin slopes in almost straight line from

umbo, anterior and posterior limits dorsal to mid horizontal

line; hinge plate moderately strong, parallel to dorsal margin,

anterior and posterior series of teeth equal in number;

ligament amphidetic and extends slightly below hinge plate

with very small anterior and posterior marginal extensions of

fused periostracum.

INTERNAL MORPHOLOGY (Fig. 38). Exhalent and inhalent

siphons combined, the inhalent siphon is shorter than the

exhalent and open at the ventral margin. There is a siphonal

tentacle to the left side. The posterior adductor muscle is oval

and approximately half the size of the crescent-shaped ante-

rior muscle. The gills are moderately well-developed and the

plates number up to 16. The labial palp ridges number

between 14-18 depending on size of individual. The foot is

large with a conspicuous byssal gland. There is a single hind

gut loop to the right of the body which has a characteristic

course that approaches an ‘S’ in shape.

Prodissoconch length: 198 1m. Maximum recorded shell

length: 5.61 mm.

Most closely resembles Y. sinuosa but without the postero-

ventral sinuosity (Fig. 139).

Fig. 36 Yoldiella blanda. Lateral view of a shell from the right side

and detail of the hinge-plate of a right valve. Specimens from Sta.

242 Argentine Basin. (Scale = 1.0 mm).

Fig. 37 Yoldiella blanda. Outline drawings of shells of differing

sizes from the right side to show change in shape with growth.

Specimens from Sta. 242 Argentine Basin. (Scale = 1.0 mm).

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 38 Yoldiella blanda. Lateral view from the right side of the

internal morphology of a specimen from Sta. 242 Argentine

Basin. (Scale = 1.0 mm). For identification of parts see Fig. 34.

Yoldiella biscayensis (new species)

TYPE LOCALITY. R.V. Chain, Cruise 106, Sta. 326, Bay of

Biscay, 22.8.1972, 50°04.9'N, 14°23.8’W, Epibenthic Trawl,

3859 m.

TYPE SPECIMEN. Holotype BM(NH) 1992024, Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta Depth No _ Lat Long Gear Date

(m)

WEST EUROPEAN BASIN

Jean Charcot

(Polygas) DS20 4226 10 47°33.0'N 9°36.7'W DS _ 24.10.72

DS21 4190 6 47°31.5'N 9°40.7';W DS 24.10.72

DS22 4144 21 47°34.1'N 9°38.4".W DS 25.10.72

DS23 4734 17 46°32.8'N 10°21.0'W DS _ 26.10.72

(Biogas II) DS31 2813 11 47°32.5’'N 9°04.2".W DS 19. 4.73

(Biogas III) DS44 3992 4 47°33.2'N 9°42.0'W DS 27. 8.73

DS41 3548 20 47°28.3’N 9°07.2,;W_ DS 26. 8.73

DS45 4260 6 47°33.9'N 9°38.4';W DS 27. 8.73

DS48 4203 2v 44°29.0'N 4°54.0'W DS _ 31. 8.73

(Biogas TV) DS53 4425 11 44°30.4'N 4°56.3’W DS 19. 2.74

DS54 4659 20) = 46°31.1'N_ 10°29.2’W_ DS 21. 2.74

DSSS 4125 76 47°34.9'N 9°40.9'W DS 22. 2.74

DS56 4050 1 4732.7'N 9°282W DS 235 2274

DS59 2790 3 47°31.7'N -9°06.2".W DS 24. 2.74

DS60 3742 24 47°26.8'N 9°07.2'W DS 24. 2.74

KR35 4140 1 47°26.0'N 9°08.7'W_ KR _ 25. 2.74

(Biogas V) DS66 3480 31 47°28.2’N 9°00.0'W DS 16. 6.74

DS67 4150 4 47°31.0'N 9°35.0'W DS_ 17. 6.74

DS68 4550 2+2v 46°26.7'N 10°23.9'W DS 19. 6.74

DS69 4510 1 44°21.9'N 4°52.4"°W DS 20. 6.74

DS70 2150 1 44°08.8’N 4°17.4";W DS 21. 6.74

(Biogas VI) DS74 2777 7 47°33.0'N 9°07.8'W DS _ 22.10.74

DS75 3250 9 47°28.1'N 9°07.8'W DS 22.10.74

DS76 4228 101 47°34.8'N 9°33.3’W DS _ 23.10.74

DS77 4240 11 47°31.8'N 9°34.6'W DS _ 24.10.74

46°31.2'N 10°23.8'W DS 25.10.74

46°30.4'N 10°27.1'W DS 26.10.74

46°29.5'N 10°29.5'W DS 27.10.74

46°28.3'N 10°24.6'W DS 27.10.74

44°25.4'N 4°52.8’.W DS 29.10.74

DS78 4706 47

DS79 4715 106

DS80 4720 19

DS81 4715 9

DS82 4462 27

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Jean Charcot CP11 4823

(Incal)

int9.347°27.9'N

int3.90S07

Chain 106

Restricted to abyssal depths in West European Basin, the

DS85 44622

CP13 31342

CP16 48251

CP17 4706 = 2

CP19 44341

CP22 4475 2

OS02 4829 2

WS03 4829 3

DS14 4254-7

4348

DS15 4211 6

DS16 4268 13

OS0S 4296- 4

4248

OS06 4316~ 5+1v

4249 12

OS08 4327 13

WS07 4281 9

WS08 4287-13

4301 =

WS09 42778

WS10 4354 18

KRO72891 8

321 2890- 2

1868

323 3356- 39

3338

326 3859 29

328 4426-13

4435

330 4632 29

4°50.8'W

9°38.0'W

10°25.0'W

10°19.5'W

4°51.3'W

4°54.8'W

15°14.6'W

15°15.7'W

15°23.3'W

— 15°22.5'W

9°35.4'W

44°23.2'N

47°34.4'N

46°27.3'N

46°30.8'N

44°24.9'N

44°22.9'N

48°20.4'N

48°19.2'N

47°32.8'N

OO SW,

— 9°38.5'W

9°33.4'W

47°33.6'N

47°29.8'N

47°30.3'N

47°31.3'N 9°34.6'W

9°34.7'W

9°36.2'W

9°36.0'W

9°34.3'W

47°32.2'N

47°27 .3'N

47°31.8'N

47°31.3'N

47°29 .8'N

47°29.5'N

47°30.6'N

47°31.2'N

47°30.5'N

47°29 .3'N

47°28.8'N

47°27.9'N

47°27 .3'N

47°28.2'N

55°02.9'N

50°12.3'N

9°32.9'W

9°38.8'W

9°37.1'W

9°35.7'W

9°33.7'W

9°34.1'W

9°34.0'W

9°39.9'W

12°43.9'W

13°35.8'W

13°53.7'W

— 13°50.9'W

14°23.8'W

15°44.8'W

50°08.3'N

50°04.9'N

50°04.7'N

50°43.5'N 17°51.7'W

50°43.3'N 17°52.9'W

30.10.74

23.10.74

26.10.74

28.10.74

30.10.74

ile

Pap

8.76

Fig. 39 Yoldiella biscayensis. Lateral view of a shell from the right

side and detail of the hinge-plate of a left valve. Specimens from

Sta. 326 West European Basin. (Scale = 1.0 mm).

majority of specimens were taken from depths greater than

3500 mm. Depth range: 2150-4829 m.

SHELL DESCRIPTION (Figs. 39-42). The form of the shell

varies somewhat from locality to locality.

Form A: The following description is based on specimens

found in Bay of Biscay at 4000 m and below.

Fig. 40 Yoldiella biscayensis. Outline drawings of shells of

different sizes from the right side to show change in shape with

growth. Specimens from Sta. 326 West European Basin. (Scale =

1.0 mm).

co ®

Fig. 41

similar size from the right side to show differences in shape.

Specimens a & b from Sta. BGVI DS 76 (4228 m); specimen c

from Sta. BG II DS 31 (2813 m). (Scale = 1.0 mm).

Yoldiella biscayensis. Outline drawings of three shells of

40 “

= ia}

WIL a qesed ape att tas ie eo 4

30 ae a ee i a 7

Length(mm)

Shell compressed, ovate, fragile, inequilateral, post-

umbonal length 48-62% of total length, sculpture of fine

irregular concentric lines, pale yellow periostracum; umbo

slightly raised, posteriorly directed; antero-dorsal margin

convex curving gradually to broadly rounded anterior mar-

gin, ventral margin evenly curved, postero-dorsal margin

very slightly sinuous, slopes gradually to distal limit of hinge

plate, then more sharply inclined to posterior margin; hinge

plate moderately long, moderately well-developed with up to

10 well developed teeth on each side of ligament, occasionally

one additional tooth in posterior series; ligament amphidetic,

large, internal, goblet-shaped, extends ventral to and some-

what posterior to proximal limit of posterior hinge plate.

Prodissoconch length: 187-198 wm. Maximum recorded

shell length: 5.82 mm.

Form B: This was taken between approximately

3000-4100 metres and at about 4000 m may be mixed with

Form A. The shell is distinguished from Form A by a more

marked concavity in the proximal part of the postero-dorsal

margin and by a more rounded posterior margin. Internally

the hinge and ligament are similar. Form B on average is

somewhat smaller than Form A.

Maximum recorded shell length: 4.19 mm.

Form C: Recorded at 2076 and 1891 metre depths. This

form is intermediate between Forms A and B. It has an

almost straight postero-dorsal margin.

Maximum recorded shell length: 7.39 mm.

INTERNAL MORPHOLOGY (Fig. 43). The three forms are

anatomically indestinguishable from each other. Exhalent

and inhalent siphons are combined. There is a siphonal

tentacle that lies either to the left or the right of the siphons.

A feeding aperture is present ventral to the siphon embay-

ment and there is a well-developed anterior marginal sense

organ.

The adductor muscles have conspicuous ‘quick’ and

‘catch’ parts. The posterior muscle is approximately half

the size of the anterior and oval in outline. The anterior

muscle is crescent-shaped. The gills are well-developed

with a relatively large number (up to 28) of gill plates

alternating on either side of the gill axis. The labial palps

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 42 Yoldiella biscayenesis.

Variation in the ratios of height

H/L, width W/L, and

postero-umbonal length PL/TLL

to length against length of the

three shape forms illustrated in

Fig. 41. Solid circles, angulate

specimens from Sta. BG VI

DS76; solid triangles, rounded

specimens from Sta. BG VI

DS76; open squares, specimens

from Sta. BG II DS31; West

European Basin.

are relatively large and, depending on the size of the

animal, have up to 25 internal ridges. The palp proboscides

are long and thin. The foot is large with a large byssal

gland. There is a small single papilla posterior to the

aperture of the gland and the posterior surface of the foot

is well-supplied with secretory cells. As in other species,

there is histological evidence of a secretion being released

along the whole length of the sole of the foot. Large,

round, pedal ganglia are situated dorsal to the byssal gland.

The visceral ganglia are ‘club’-shaped and relatively slen-

der, the cerebral ganglia are slightly more inflated. The

oesophagus, stomach and style sac are similar to those

described for other Yoldiella species, the hind gut is

relatively broad and forms a single loop on the right side of

the body. The posterior section of the loop describes a

conspicuous and characteristic ‘S’-shaped course. There is

a typhlosole along the length of the hind gut. The digestive

diverticula are similar to those of other species of Yoldiella.

The sexes are separate. All individuals more than 3.0 mm

in length show some gonadial development. A specimen

4.9 mm in length contained 190 ova (maximum diam. 150

wm).

Most closely resembles Y. sinuosa and Y. blanda and

distinguished by more angulate postero-dorsal margin and

lack of postero-ventral sinuosity.

Yoldiella lata (Jeffreys 1876)

TYPE LOCALITY. Valorous Sta. 9, Davis Strait, 14.8.1875,

59°10'N, 50°25’W, dredge, 1750 fms.

TYPE SPECIES. Lectotype: U.S. Natl. Mus., No. 199695 as

here designated.

Specimens from Biogas Sta. DS87 are housed in the

Museum National d’Histoire Naturelle, Paris.

Leda lata Jeffreys 1876, p. 431 (in part).

As is pointed out under Y. jeffreysi (p. 63) when the

‘Valorous’ material was examined, it was found that two

species had been grouped together under the name Leda /ata.

Furthermore, the original description is such that it is not

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Fig. 43 Yoldiella biscayensis. Lateral view from the right side of

the internal morphology of a specimen from Sta. BG VI DS76

West European Basin. (Scale = 1.0 mm). For identification of the

parts see Fig. 34.

possible to identify which of the two is L. lata. We have

separated the two species and chosen lectotypes from the

‘Valorous’ material.

MATERIAL.

Cruise Sta’ DepthNo Lat Long Gear Date

(m)

WEST EUROPEAN BASIN

Sarsia 44 1739 18 43°40.8’N 3°35.2’W ED 16. 7.67

65 1922) .25,- »46915.0'N... 4°50:0'W ED. .25.. 7.67

La Perle

(BiogasI) DS06 5

DS07 2

DS11 2205 8 47°35.5'Ne 8°33.7' WDS 8. 8.72

DS12 2180 2.) GATIZEISING 83355! W © DSP “9ON8G72

DS13 2165 5+1v 47°33.7'N 8°39.9'W DS _ 9. 8.72

OSO01 2v OS

Chain106 313 1491— 457 51°32.2’N 12°35.9'W ES 17. 8.72

1500

316 2173-1653 50°58.7'N 13°01.6'W ES 18. 8.72

2209

Jean Charcot

(Polygas) DS15 2246 8 47°35.2'N 8°40.1'W DS _ 21.10.72

DS16 2325 le SAT S6uIUN ee G40: We DS) 21510572

DS18 2138 10 47°32.2'N 8°44.9'W DS 22.10.72

DS25 2096 255 44°08.2'N 4°15.7'W DS | 1.11.72

DS26 2076 1095 44°08.2'N 4°15.0’'W DS __ 1.11.72

+17v

CV10 2108 24 49°30-7'N, (840'6'W CV 22.20.72

Jean Charcot

(Biogas II) DS32 2138 26 47°32.2’N 8°05.3’W DS 19. 4.73

(Biogas IIT) DS35 2226 9 47°34.4’N 8°40.7'W DS 24. 8.73

DS36 2147 7+2v 47°32.7'N

DS37 2110 12+2v 47°31.8'N

DS38 2138 13 47°31.5'N

DS49 1845 177+ 44°05.0'N

8°36.5'W DS 24. 8.73

8°34.6'W DS 24. 8.73

$735.8) Wal DSi25. 8313

BIS OAM, IDS) ale G78)

DSS0 2124 et 44°09.9'N 4°15.9'W DS 1. 9.73

(Biogas IV) DSS51 2430 OE 44°11.3’N 4°15.4°;W_ DS 18. 2.74

DS52 2006 tee 44°06.3’N 4°22.4';W DS _ 18. 2.74

DS61 2250 ae 47°34.7'N —8°38.8'W_ DS 25. 2.74

DS62 2175 48+1v 47°32.8'N 8°40.0'W DS _ 26. 2.74

Jean Charcot DS64 2156 12+ 47°29.2'N 8°30.7'W DS_ 26. 2.74

14v

CV33 1913 1 44°04.6'N 4°18.1'W CV 18. 2.74

CPO01 2245 19+4v 47°34.6’N 8°38.8’'W CP 25. 2.74

(Biogas V) DS70 2150 6 44°08.8’'N 4°17.4‘;W DS 21. 6.74

CP07 2170 136+ 44°09.8’N 4°16.4‘W CP 21. 6.74

(Biogas VI) DS71 2194 19 47°34.4'N 8°33.8'W DS_ 20.10.74

DS86 1950 325+ 44°04.8'N

13v

DS87 1913 550+ 44°05.2'N

4yv

DS88 1894 40+2v 44°05.2'N

CP08 2177 12+1v 44°33.2'N

CP09 2171 34 47°33.0'N 8°44.1’W CP 20.10.74

CP24 1995 23 44°08.1’N 4°16.2’W CP 31.10.74

Jean Charcot CP01 2068— 29 55°57.0'N 10°55.0'W CP 16. 7.76

4°13.7'W DS 31.10.74

4°19.4°;W DS 1.11.74

4°15.77W DS 1.11.74

8°38.5’'W CP 20.10.74

2040

(Incal) CP02 2091 4 57°58.4'N 10°42.8'W CP 16. 7.76

— 57°57.7'N_ 10°44.6'W

CP08 2644 1 50°14.7'N 13°13.5’W CP 27. 7.76

- 50°15.2'N 13°14.8'W

QSO1 2634 2 50°14.4’'N 13°10.9'W OS 30. 7.76

— 50°15.2'N 13°11.0'W

37°59: N 10°39:8'W DS 15. 7-76

— 57°59.2'N 10°41.3'W

57°58.8'N 10°48.5'W DS 16. 7.76

— 57°58.5'N 10°49.2'W

56°28.1'N 11°11.77;W DS _ 18. 7.76

— 56°17.6’N_ 11°12.0'W

56°26.6’N 11°10.5'W DS 18. 7.76

— 56°15.9'N 11°10.7"W

DSO1 2091 234

DS02 2081 262

DS05 2053. 7

DS06 2494 86

WS01 2550- 6 50°19.4’N_ 13°08.0'W WS 30. 7.76

2539 — 50°19.3’N 13°06.9'W

WS02 2498— 4 50°19.3’N 12°55.8'W WS 30. 7.76

2505 — 50°20.0'N 12°56.0'W

CANARIES BASIN

Discovery 6701 1934 9

SIERRA LEONE BASIN

AtlantisI] 139 2099-1

31 2187

27°45.2'N 14°13.0'W ED 16. 3.68

10°33.0"N' "17°S8:0"W ES” 4. 2.67

Largely restricted to lower slope and abyssal rise depths in

the northeastern Atlantic, but predominantly in the West

European Basin with a few specimens taken in the Canaries

and Sierra Leone Basins. Depth range: 1491-3220 m.

SHELL DESCRIPTION (Figs. 44 & 45). Shell transversely

ovate, fragile, inequilateral, postumbonal length 53-65%

of total length, moderately inflated, very fine concentric

lines forming ridges ventrally, more conspicuous in larger

specimens, irridescent, pale yellow/brown periostracum,

light and dark banding patterns; umbo moderately inflated,

inwardly directed; dorsal margin raised, anterior and pos-

terior margins smoothly curved with anterior margin more

convex than posterior, antero-dorsal margin short, joins

anterior margin in smooth curve, postero-dorsal margin

approximately straight, gradually inclining distally to pos-

terior limit of hinge plate, then curves sharply to posterior

Margin, posterior margin more convex dorsally, ventral

margin smoothly curved; hinge plate narrow, anterior and

posterior hinge plates merge with margin below umbo,

teeth small, chevron-shaped, number on each plate

depending on size (up to 9/10), usually with one or two less

on anterior hinge plate; ligament amphidetic, small, inter-

nal rectangular in cross-section.

Prodissoconch length: 198 wm (average) range 190-220

wm. Maximum recorded shell length: 4.43 mm.

Fig. 44 Yoldiella lata. Lateral view of a shell from the right side

and detail of the hinge-plate of a right valve. Specimens from Sta.

316 West European Basin. (Scale = 1.0 mm).

Fig. 45 Yoldiella lata. Right lateral and dorsal views of shells to

show changes in shape with growth. Specimens from Sta.

INCAL/DS 06 West European Basin. (Scale = 1.0 mm).

The shell is similar in shape to Yoldiella jeffreysi but more

fragile, more compressed, and has fewer hinge teeth on a

narrower hinge plate. With increasing length there is a

gradual increase in the posterior umbonal length/total length

ratio. There is little change in the height/length or width/

length ratios (Fig. 46). Hydroids are present on several

specimens at the antero-ventral shell margin.

INTERNAL MORPHOLOGY (Fig. 47). With the exception of the

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

} Woon Sa aptagan 2.

fe ‘glint 25

15 No.

2 3 4

Length

Fig. 46 Yoldiella lata. Variation in the ratios of height H/L, width

W/L and postero-umbonal length PL/TL to length against length

of a sample from Sta. BG V CP 07 from the West European

Basin.

Fig. 47 Yoldiella lata. Lateral view from the right side of the

internal morphology of a specimen from Sta. BG III DS 50 West

European Basin (Scale = 1.0 mm). For identification of parts see

Fig. 34.

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

posterior margin, the mantle edge is little modified and

comprises three marginal lobes. The middle sensory lobe

forms a frill while the inner muscular fold is thickened, being

approximately twice the thickness of the general mantle

epithelium and is relatively broad. Posteriorly combined

exhalent and inhalent siphons are formed by fusion of the

opposing inner muscular lobes. The inhalent siphon is shorter

than the exhalent siphon and remains open ventrally. The

siphonal wall is relatively thin. A narrow band of longitudinal

muscles lies immediately internal to the basal membrane of

the outer and inner epithelia. Internal to the longitudinal

fibres are circular and transverse muscle fibres with sub-

epithelial gland cells scattered throughout the layer. Between

the exhalent and inhalent siphons, there is a pair of haemo-

coelic channels within the muscle layer (Fig. 48a). The

proximal end of the gill axes join laterally at the junction

between the siphons, The gill axes probably act as a channel

to guide faecal rods into the lumen of the exhalent siphon.

The anus lies immediately dorsal to the inner margins of the

siphon.

The siphonal tentacle, is developed from the middle sen-

sory lobe of the mantle and originates from a pocket in the

siphonal embayment at the base of the siphon, usually on the

left side. It consists of an elongate finely-tapering cone which

in transverse section comprises a large central nerve sur-

rounded by several muscle fibres (Fig. 48b). These in turn are

surrounded by a layer of connective tissue with gland cells

interspersed throughout and a layer of epithelial cells with

fine granular contents.

Ventral to the siphon is a broad, deep, specialized area of

the mantle — the feeding aperture. Ventral to the inhalent

aperture there is an inner secondary muscular fold. Peripheral

to this the inner muscular layer is enlarged both in thickness

and width. In preserved specimens this area is highly convo-

luted. In life the muscular and sensory layers are probably

extended beyond the shell margin as a flap on each side. The

epithelial cells in this region are densely ciliated (Fig. 48a).

The adductor muscles are unequal in size with the ‘quick’

and ‘catch’ parts obvious. The posterior adductor is round in

Fig. 48 Yoldiella lata. Transverse sections through a, the inhalent,

exhalent and feeding apertures; b, the base of the siphonal

tentacle; c, the anterior sense organ of a specimen from Sta. BG

III DS 49 West European Basin. (Scales = 0.1 mm).

outline. The anterior is approximately twice the size of the

posterior and crescent-shaped. At the mantle margin ventral

to the anterior adductor muscle there is a well-developed

anterior sense organ. This is derived from the middle sensory

fold which is greatly extended to form two flaps. The epithe-

lial cells of the outer flap are ciliated. Internal to this the

epithelium is glandular (Fig. 48c). Underlying this epithelium

is a thick layer of connective tissue containing the pallial

nerve.

The gills lie parallel to the postero-dorsal shell margin.

They are well-developed with up to 22 alternating gill plates

(the number relates to the size of the individual).

The labial palps are moderately large and, also depending

on the size of the animal, have up to 24 ridges on their inner

face. The palp proboscides are relatively slender. The palps

are wedge-shaped and extend 1/4-1/2 way across the body.

The mouth is set posterior to the anterior adductor muscle.

The foot is well-developed, and of typical nuculanid form.

The divided sole is elongate with papillate edges. At the tips

of the papillae, lying between muscle fibres are glandular

cells with ducts to the surface of the foot. Secretions from

these may be used to lubricate the movement of the foot

through the sediment. A large well-developed byssal gland is

present in the heel of the foot (Fig. 49a). The byssal gland is

spherical, composed of large, hyaline cells, surrounded by

muscle fibres. It opens medially at the posterior limit of the

divided sole and several glandular epithelial cells surround

the opening. A very small medial papilla lies posterior to the

opening at the heel of the foot. Histochemical tests have been

carried out to identify type secretion from the gland. Tests

did not confirm any protein component but this could have

been masked by other muco-substances. The main compo-

nent at the centre of the byssal gland appears to be a

keratin-sulphate (PAS-ve with no glycol groups, and carboxyl

groups). It has the character of cartilage. (Secretions from the

gland cells in the foot do, however, possess carboyxyl

groups).

The posterior pedal retractor muscles comprise a thick,

wide, strap that inserts on the shell on either side of the hind

gut anterior to the posterior adductor muscle. A small

postero-lateral pedal retractor muscle is present on either

side of the stomach. Three major pairs of anterior pedal

retractor muscles pass from the neck of the foot anteriorly to

insert posterior to the anterior adductor muscle on either side

GS PSA

Fig. 49 Yoldiella lata. a, transverse section through the heel and

‘byssal’ gland of the foot and b, right and left lateral external

views of the stomach and style sac of specimens from Sta. Polygas

DS 26 West European Basin. (Scales = 0.1 mm).

of the oesophagus and lateral to the hind gut loop.

The cerebral ganglia are relatively small and oval while the

visceral ganglia are elongate and relatively thickened. The

pedal ganglia are large and elongate/oval, conjoined, and

each has a large dorsal statocyst associated with it and which

contains numerous small refractile crystals.

The mouth is displaced posteriorly to a small extent. It

opens into a relatively long, ciliated oesophagus which curves

first anteriorly to the posterior face of the anterior adductor

before passing posteriorly to the stomach. The oesphagus is

positioned almost centrally rather than dorsally within the

body. The longitudinal axis of the stomach and style sac lies

diagonally within the body, the style sac penetrating into the

upper half of the foot. The stomach and style sac are large,

taking up much of the central body space. Externally the

stomach is brown in colour. A large gastric shield covers part

of the dorsal wall and extends laterally, mainly to the left

side. To the right of it are approximately nine sorting ridges.

The organization of the stomach appears similar to that

described for Ledella (Allen & Hannah, 1989). The stomach

is cradled by the pedal retractor muscles. The digestive

diverticla are in three parts which for the most part lie

anterior to the stomach but also to the right and left of the

body. A duct from the right diverticulum joins the stomach

on the right anterior face just ventral to the oesophageal

opening. Immediately posterior to this, a duct from one of

the two left diverticula enters the stomach on the lower left

side (Fig. 49b). The third diverticulum opens into the stom-

ach immediately below the tooth of the gastric shield. The

epithelial cells which line these ducts contain highly refractile

golden granules. In the case of the third diverticulum the duct

is reduced to a small collar of cells around the aperture.

Material was present in the lumen of this diverticulum but not

in the other two diverticula.

From the style sac, the hind gut passes posteriorly into the

foot, as far as the pedal ganglia. It then passes anterior for a

short distance between ganglia and byssal gland and then

takes a dorsal course parallel to the posterior margin of the

foot to a point immediately ventral to the ligament. It then

forms a loop on the right side of the body which skirts the

posterior face of the anterior adductor and then passes

dorsally and posteriorly parallel to shell margin to the anus.

A deep typhlosole is present along the entire length of the

hind gut. Slight variations in the arrangement of the loop of

the hind gut are seen in this species. Material in the gut

consists of fine clay particles and skeletal fragments of various

kinds.

The sexes are separate. The gonads overlie the lateral and

dorsal sides of the viscera of the body. Gonads are present in

all specimens over 2 mm in length. Numbers of ova are

relatively high and vary with the size of the animal. A

maximum of c.730 ova were counted in a specimen 3.54 mm

in length. The maximum observed diameter of the ova range

from 126-190 pm. There is some indication of an annual

reproductive cycle. Ova of maximum size were present in

October and February. April and June samples show little

ovarian development, but increasing maturity was observed

in July and August. The gonadial apertures open into the

supra-mantle cavity, close to those of the kidney, anterior to

the posterior pedal retractor muscle.

The kidney is well-developed. It lies anterior to the poste-

rior pedal retractor muscle and extends on either side of the

stomach, tapering to its anterior limit close to the lateral

pedal retractor mucles. The kidney epithelium is a single

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

layer of cuboid cells. The heart, through which the hind gut

Passes is well-developed in this species with numerous muscle

fibres in a relatively thick-walled ventricle.

Distinctive features include the hind gut on the right hand

side of body forming an extended single loop which turns

back on itself; the light and dark banding pattern of shell, and

the more rounded posterior adductor muscle. The hind gut,

although similar, is simpler in form than that in Yoldiella

Jeffreysi.

Yoldiella frigida Torrell 1859

TYPE LOCALITY. Spitzbergen, Ice Sound 55 m.

TYPE SPECIMEN. Holotype not known; lectotype (desig. A.

Warén, 1989) Swedish Museum of Natural History No. 1986.

Yoldia frigida Torrell 1859, p.148, pl. 1, Fig. 3; Friele 1878, p.

222; Leche 1878, pl. 1, Fig. 6 a—-d; Sars G.O. 1878, pl. 4,

Fig. 11a—b; Friele 1879, p. 266.

Leda frigida Jeffreys 1870, p. 440; Jeffreys 1879, p. 570.

Portlandia frigida Norman 1893, p. 344, p. 364; Posselt 1898,

p. 34-35; Friele & Grieg 1901, p. 15; Hogg 1905, p. 112;

Jensen 1905, p. 320; Grieg 1909, p. 534; Ohdner 1915, pl.

1, Figs. 30-32;

Portlandia frigida Grieg 1916, p. 8; Ockelmann 1958, pl. 1.

Fig. 14.

Portlandia (Yoldiella) frigida Soot-Ryen 1939, p. 9; Clarke

1963, p. 100, pl. 2, Figs. 6-8.

Yoldiella frigida Soot-Ryen 1958, p. 10; Warén, 1989; Figs.

TE & F&10G&H.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

NORTH AMERICAN BASIN

Atlantis 4 400 304 39°56.6'N 70°39.9'W AD 30. 8.62

Chain 58 105° 530) «121 39%56.6/N 71203:6. WE 528506

Chain 88 207 «805S— 153 39°51.3°N—70°54.3'W ES = 21° 2°69

811 — 39°51.0'N 70°56.4’'W

WEST EUROPEAN BASIN

Thalassa 2425 700 1 48°28.9'N 09°44.0’'W PBS 25.10.73

Jean Charcot DS04 619 1 57523:0'N 110720 W DSS 17.6:76

Incal DS03 609 16° S7°25-N 11°03. 7 Wr SDS: 6-76

In addition to the above, material from Ingolf Sta. 115 (det

Ockelmann), Spitzbergen, Franz Joseph Fjord, East Green-

rand (USNM No. 219726 det. Odhner) and off Martha’s

Vineyard Sta. 934 (USNM No. 193343 det. Verrill & Bush)

has been examined.

Predominantly a North Atlantic high arctic species from

shelf seas and upper slope depths (Warén (1989). Clarke

(1963) reports it as being present at abyssal rise depths but

there must be some doubt about this. There is some indica-

tion that in north temperate seas at the southern extremity of

its range the population is found deeper at the shelf slope

break, thus suggesting a relationship with temperature.

Greenland, Jan Mayen, Spitzbergen, Novaya Zemlya, Kera

Sea, West Siberia, Iceland, North American and West Euro-

pean Basins (see Ockelmann (1958) for other more doubtful

records). Depth range: 5-811 m.

SHELL DESCRIPTION (Fig. 50 & 51). Shell subelliptical,

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

approximately equilateral (postumbonal length 45-50% of

total length), smooth, moderately thin, pale yellow irrides-

cent periostracum, with banding patterns, narrow dark bands

and broader light bands between; umbo slightly raised

directed somewhat posteriorly; dorsal margins proximally

straight, distally curving to anterior and posterior margins,

posterior and anterior dorsal margins very slightly angulate at

limit of hinge plate, limit of anterior margin submedial, limit

of posterior margin supramedial, postero-ventral margin rela-

tively flattened, very slightly sinuous particularly in larger

specimens; hinge plate relatively short, not extending beyond

inner margin of adductor muscles, 5 anterior teeth and 6

posterior teeth in specimen 2.5 mm, ventral part of chevron

reduced; ligament amphidetic, large elongate internal part,

with small external extensions either side of umbo; adductor

muscle scars distinct, particularly anterior, line of attachment

of pallial sinus also visible. Hydroids may be present, dor-

sally, close to umbo and on the posterior and postero-ventral

margins.

Prodissoconch length: 166-208 4m. Maximum recorded

: 7

Fig. 51 Yoldiella frigida. Lateral views of left valves showing detail

of the ligament and the hinge-plates; a, a specimen from Stor

Fjord Spitzbergen (USNM No. 219726); b, a specimen from Sta.

105 North America Basin. (Scale = 1.0 mm).

Fig. 50 Yoldiella frigida. Lateral

views of shells from the right side.

Specimens a & b from Franz Joseph

Fjord, E. Greenland; c, from Sta.

INCAL DS 04 Bay of Biscay; d, from

off Martha’s Vinyard (USNM No.

193343). (Scale = 1.0 mm).

shell length: 3.98 mm, (Sta. 207), however, specimens from

Greenland donated by Ockelmann measure 6.1 mm.

Comparing height/length, width/length and post-umbonal

length/total length ratios of specimens from the North Ameri-

can Basin (Sta. 105 & 207) and West European Basin (Incal

DS03), it was found that in the latter case the average for

each of the three parameters is slightly less than those from

the two North American Stations and whose ranges for the

most part overlap (Figs. 52 & 53). Specimens from Sta. 105

appear to be somewhat wider than specimens from Sta. 207.

It is highly likely that many records of Y. frigida from the

North Atlantic relate to other species. This is a view also

expressed by Warén (1989). For example, Y. frigida (USNM

No. 193343) figured by Verrill & Bush (1898) and here (Fig.

50), closely resembles Yoldiella nana again confirming the

observations of Warén (1989). (Y. nana has a straighter

dorsal margin, a slightly more inflated umbo and fewer hinge

teeth). Further comparing USNM No. 193343 with high arctic

specimens of Y. frigida the former has a larger umbo, and

thicker hinge. In addition, we believe that many shallow

water specimens of Yoldiella inconspicua from the North

American Basin have been misidentified as Y. frigida. Subtle

differences seen here, as in many other deep-sea protobranch

bivalves, are particularly difficult to disentangle (Fig. 53) and

in the case of Yoldiella this particularly applies to species

found at shallower slope depths.

INTERNAL MORPHOLOGY (Fig. 54). Mantle structures include

a well-developed anterior sense organ and long slender

combined siphons with a single lumen. A siphonal tentacle is

present originating, but not without exception, on the left

side of the inner limit of the siphon embayment. The adduc-

tor muscles are unequal in size the anterior being the some-

what larger and oval in outline whereas the posterior muscle

is more circular in outline. The gill axes attach ventrally to the

siphon and with the exception of the ventral margin, the

latter must be assumed to be largely exhalent in origin. There,

is a well-developed feeding aperture ventral to the siphon.

The gills are well-developed, the number of filaments range

from 12-22 according to the size of the specimen. The palps

are large and extend over approximately half the length of the

body. There are between 11 and 20 relatively broad palp

ridges and the palp proboscides are also well-developed. The

50 “

a A

r A

WIL . ai ae

a rane a “: ee 3 =

“ age ek a a

a A

H\L . a AA 4 4

a a A a a

ana ji a Ss a a

a a a

foot which tends to be largely hidden by palps is also

relatively large with well-developed retractor muscles. This is

particularly true of the anterior series. There is a moderate-

sized byssal gland. The pedal ganglia are elongate each with a

large statocyst dorsal to it. The visceral ganglia lie relatively

ventral in position, distant from the posterior section of the

hind gut. The visceral and the cerebral ganglia are not

particularly large.

The gut describes a single loop on the right side of the

body. The size of the hind gut and the path it describes on the

right side of the body is highly characteristic of a species even

in those with a single loop and is particularly useful in

distinguishing, for instance, Y. frigida from Y. inconspicua

(Figs. 53 & 63). The oesophagus is particularly wide in

cross-section, the stomach is large with two sorting areas

clearly visible to the right side of the gastric tooth. The more

ventral of the two, which has not been observed in other

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 52 Yoldiella frigida. Variation in ratios of

height H/L, width W/L and postero-umbonal length

PL/TL to length against length of samples from;

open triangles, Sta. 105 North America Basin;

closed triangles, Sta. INCAL DS 03 Bay of Biscay;

closed circles Sta. 207 North America Basin.

Fig. 53 Yoldiella frigida. Outlines of shells

from the right side from three Stations to

show variation in shape within and between

populations and with increasing size.

Specimens from a, Sta. Ingolf 115 (det

Ockelmann); b, Sta. 105 North America

Basin; c, Sta. INCAL DS 03 Bay of Biscay.

(Scale = 1.0 mm).

species, is broad and close to the aperture of the right

digestive duct. Ingested material was seen in the dorsal part

of the left digestive diverticulum. The duct to the right

digestive diverticulum overlies the dorsal section of the hind

gut. The kidney is well-developed and the pericardial cavity is

large.

The sexes are separate. The developing gonads surround

the hindgut loop in the usual manner. In one sectioned

specimen (2.3 mm total length) 59 ova were present with a

maximum diameter of 120 4m. The ova were present ventral

and internal to the digestive diverticula, with fewer numbers

overlying the viscera dorsally.

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Yoldiella robusta (new species)

TYPE LOCALITY. R.V. Atlantis II, Cruise 60, Sta. 280,

36°18.0’S,

Argentine Basin, 29.3.1971, 5523.9 W,,

Epibenthic Trawl, 256-293 m.

DP %

Fig. 54 Yoldiella frigida. Lateral view from the right side of the

internal morphology of a specimen from Sta. 105 North America

Basin. Inset is a right-frontal external view of the stomach. (Scale

= 1.0 mm). For identification of parts see Figs. 34 & 49.

Fig. 55 Yoldiella robusta. Lateral view of a shell from the right

side and detail of hinge-plate of a left valve. Specimens from Sta.

280 Argentine Basin. (Scale = 1.0 mm).

TYPE SPECIMEN. Holotype : BM(NH) 1992030, Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

ARGENTINE BASIN

Atlantis 11 280 256— 3495 36°18.0’'S

293

53723. 9°Wi ES 29:37

Restricted to one Station at the shelf/slope break of the

Argentine Basin. Depth range: 256-293 m.

SHELL DESCRIPTION (Figs. 55 & 56). Shell subovate, moder-

ately inflated, irregular concentric growth lines and small

ridges best developed posteriorly, periostracum pale yellow;

umbos anterior to mid line, slightly raised and inwardly

Fig. 56 Yoldiella robusta. Outlines of shells from the right side to

show change in shape with growth. Specimens from Sta. 280

Argentine Basin. (Scale = 1.0 mm).

Fig. 57 Yoldiella robusta. Lateral view from the right side of the

internal morphology of a specimen from Sta. 280 Argentine

Basin. (Scale = 1.0 mm). For identification of parts see Fig. 34.

directed; proximal antero-dorsal margin horizontal for very

short distance before curving steeply to anterior margin,

proximal postero-dorsal margin horizontal or slightly convex,

distally slightly angled opposite posterior limit of hinge,

postero-ventral margin slightly sinous giving a relatively

narrow rounded medial tip to posterior margin, ventral

margin smooth convex curve. Hinge plate short, moderately

narrow with up to 9 small chevron-shaped teeth on each

series, one additional tooth on posterior plate. Ligament

large, amphidetic, bilobed in lateral view, with short, narrow,

secondary external extensions anterior and posterior to

umbo.

Prodissoconch length: c. 200 wm. Maximum recorded shell

length: 4.0 mm.

Shell measurements (mm) & ratios are as follows:-

Length Height Width H/L W/L

1.89 iL Sil 0.70 0.70 0.37 0.51 -

2.58 1.76 0.98 0.68 0.38 0.53 =

2.62 1.80 0.94 0.69 0.36 0.56 -

2.81 1.89 1.09 F677 039055 -

3.05 2.05 1.23 0.67 0.40 0.54

3.44 2.21 0.64 - = 0.57 8/9

S255) 2.38 1.44 0.67 0.40 0.55 =

3.61 2.46 0.68 = = 0.53 7/8

3.81 2.67 52 0.70 0.40 0.56 -

3.98 2.62 1.58 0.66 0.40 0.59 -

INTERNAL MORPHOLOGY (Fig. 57). The internal morphology

is very similar to that described for Y. frigida. The siphons are

combined and there is a siphonal tentacle to the left. The

anterior sense organ is well-developed. The adductor muscles

are relatively large, the posterior being more round and

slightly smaller than the anterior muscle. The foot is also

large with a moderately-sized byssal gland. The gills are well

developed and suspended more ventral within the mantle

cavity than other species. There are approximately 15 alter-

nating gill filaments. The labial palps extend across about half

the body and have 12-16 internal ridges and well-developed

palp proboscides. The visceral and cerebral ganglia are

relatively large. The viscera are also more ventral in position

than in most other Yoldiella species. The pedal ganglia are

large and elongate. The hind gut forms a single loop on the

right side of the body.

Yoldiella extensa (new species)

TYPE LOCALITY. R.V. Atlantis II, Cruise 60, Sta. 245,

Argentine Basin, 14.3.1971, 36055.7’S, 53001.4’W,

Epibenthic Trawl, 2707 m.

TYPE SPECIMEN. Holotype: BM(NH) 1992036, Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta. Depth No Lat Long Gear Date

(m)

ARGENTINE BASIN

AtlantisII 245 2707 26 36°55.7'S 53°01.4'W ES 143.71

Only found at the one Station at abyssal depth in Argentine

Basin. Depth range: 2707 m.

PL/TL __ Teeth(A/P)

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 58 Yoldiella extensa. Lateral view of a shell from the right side

and detail of the hinge-plate of a right valve. Specimens from Sta.

245 Argentine Basin. (Scale = 1.0 mm).

SHELL DESCRIPTION (Figs. 58 & 59). Shell oblong-ovate,

moderately robust, moderately inflated, nearly equilateral,

very fine concentric lines, periostracum pale yellow; umbo

inflated, raised slightly, directed posteriorly; dorsal margin

slightly convex, antero-dorsal margin gradually slopes to

broad rounded anterior margin, ventral margin long, curva-

ture similar to that of dorsal margin, posterior margin slightly

extended with faint suggestion of postero-ventral sinus; liga-

ment amphidetic, moderate size, elongate, but slightly asym-

metric in lateral view with posterior part slightly longer and

wider than anterior, slight external extension on either side of

umbo; hinge plate narrow, relatively short, with small eden-

Fig. 59 Yoldiella extensa. Outlines of shells from the right side to

show change in shape with growth (see also Fig. 58). Specimens

from Sta. 245 Argentine Basin. (Scale = 1.0 mm).

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

tulous space below umbo, anterior plate follows curvature of

antero-dorsal margin, posterior plate with slight convex arch,

equal number of teeth on each plate, teeth with prominent

dorsal arm and reduced ventral arm.

Prodissoconch length: c 170 1m. Maximum recorded shell

length: 4.62 mm.

Shell measurements (mm) & ratios are as follows:-

Length Height Width H/L W/L PL/TL

2.56 1.81 1.26 0.70 0.49 0.51

2.60 1.76 1.22 0.68 0.47 0.53

INTERNAL MORPHOLOGY (Fig. 60). The siphons are com-

bined, with a single lumen present. A siphonal tentacle

occurs on the right side of the siphonal embayment. The

adductor muscles are unequal in size the anterior being one

and a half to two times larger in cross-section than the

posterior. Both are more or less oval in shape. The gills are

well-developed with 13-16 plates. The labial palps are small

in the contracted state, extending about 1/4 distance across

body, and have 8-10 moderately narrow palp ridges. In

contrast the palp proboscides are well-developed. The pedal

ganglia are large and elongate, similarly the visceral and

cerebral ganglia are also well-developed. They are club-

shaped with the cerebral ganglia being slightly larger than the

visceral. The foot is long and narrow, with a large byssal

gland in the heel. The stomach is large and there is a single

hind gut loop on the right side of the body.

Yoldiella inconspicua inconspicua Verrill & Bush 1898

TYPE LOCALITY. Off Martha’s Vineyard, 318 fm. Original

specimens were taken from North American Basin between

Lat. 42°33'N, Long. 69°58.5’'W and Lat. 35°12.10’N and

74°57.15'W by the U.S. Fish Commission Steamers Fish

Hawk and Albatross.

Fig. 60 Yoldiella extensa. Lateral view from the right side of the

internal morphology of a specimen from Sta. 245 Argentine

Basin. (Scale = 1.0 mm). For identification of the parts see Fig.

34.

TYPE SPECIMEN. Holotype: U.S. Natl. Mus. No. 48867.

Yoldiella inconspicua Verrill & Bush 1898, p. 869, pl. 79,

Figs. 5-3.

Yoldiella nana Warén 1989 (in part), p. 227.

MATERIAL.

Cruise Sta. Depth No Lat Long Gear Date

(m)

WEST EUROPEAN BASIN

Sarsia S44 1739 11 43°40.8'’N

S50 2379 343 43°46.7'N

Jean Charcot DS20 4226 2 47°33.0'N

(Polygas) DS21 4190 Seay Sl uIN

DS22 4144 3 47°34.1'N

335.2, W ED) 16. 7267

3°38.0'W ED 18. 7.67

9°36.77'W DS 24.10.72

9°40.77;W DS 24.10.72

9°38.4’W DS 25.10.72

DS28 4413 2 44°23.8'N 4°47.5'W DS © 2.11.72

Chain 106 316 2173— 20 50°58.7’N 13°01.6'W ES 18. 8.72

2209

318 2868- 72 50°04.9'N 14°23.8’W ES 20. 8.72

2890 — 50°05.3’N 14°24.8"W

323 13338 16 SO0%083'Ne 137537°W SES 21. 8572

3356 — 50°08.3’N = 13°50.9'W

326 3859 3° 50°04:9’N 14°23.8'W ES 22. 8.72

— 50°05.3’N 14°24.8"W

330 4632 30 50°43.5'N 17°51.7'W ES 24. 8.72

— 50°43.4'N — 17°52.9'W

11°04.0'W ES 4. 7.73

5°07.2;,W DS 26. 8.73

Challenger 10 2540 1 56°36.0'N

Jean Charcot DS41 3548 5 47°28.3'N

(Biogas III)

(BiogasIV) DSSS 4125 58 47°34.9'N 9°40.9".W) DS 22. 2.74

(Biogas V) DS66 3480 3 47°28.2'N 9°00.0'W DS 16. 6.74

DS67 4150 4730.0'N 9735.05W . DS, 172 6.74

(Biogas VI) DS71 2194 1 47°34.3'N = 8°33.8'W_- DS_—.20.10.74

DS75 3250 1 47°28.1'N 9°07.9'W DS 22.10.74

DS76 4228 26 47°34.8'N 9°33.3'W DS _ 23.10.74

CP13 4134 4 47°34.4'N — 9°38.0'W CP 23.10.74

DS77 4240 1 47°31.8'N 9°34.6'W DS 24.10.74

DS82 4462 1 44°25.4'N = 4°52.8'W_ DS 29.10.74

(Incal) DS01 2091 2 ST S9-G UN LUSsore WW. ese lone 370

= 57°59.2'N 10°41.3"'W

DS02 2081 4 57°58.8'N 10°48.5'W DS 16. 7.76

— 57°58.5'N 10°49.2'W

C003 2466 12 56°38.0’'N 11°64.0'W CP 17. 7.76

— 56°37.3’N_ —11°07.8’W

C004 2483— 9 56°33.2’N 11°11.3’W CP 17. 7.76

1513 — 56°32.5'N 11°12.4"W

DS05 2503 270 56°28.1’N 11°11.7';W DS _ 18. 7.76

— 56°27.6’N 11°02.0'W

DS06 2494 277 56°26.6’N 11°10.5'W DS_ 18. 7.76

— 56°25.9'N _11°10.7'W

DS07 2884 280 55°00.7’N 12°31.0'W DS _ 19. 7.76

— §5°01.0’N 12°21.0'W

DS08 2891 58 55°02.0’N 12°34.6';W DS 19. 7.76

— 52°01.9'N 12°33.4"W

CPO0S 2884 149 55°00.4"'N 12°29.4".W CP 19. 7.76

— 55°00.9’N 12°31.1"W

CP06 2888— 218 55°02.3’N 12°40.3'W CP 19. 7.76

2893 — 55°02.6'N 12°41.7'W

KR06 2891 1 55°02.9'N 12°43.7’'W KR _ 20. 7.76

— 55°02.2’N 12°39.0'W

KRO7 2891 1 S520229"N 12-439! W KRY 2057276

— 55°02.2’N 12°39.0’W

CP07 2895 488 55°03.4’N 12°46.2".W CP 20. 7.76.

— 55°04.4'N — 12°46.7'W

DS09 2897 867 55°07.7'N 12°52.6';W DS 20. 7.76

— 55°08.1’N 12°53.2'W

CP08 2644 135 50°14.7'N 13°13.5'W CP 27. 7.76

— 50°15.2'N = 13°14.8'W

DSLOW719 9 21 Ss0N257N 13166!W DS 27557576

— 50°13.2'N 13°16.4’W

QS01 2634 322 50°14.4’N 13°10.9.W OS 30. 7.76

— 50°15.2'N —13°11.0’W

WS01 2550 221 50°19.4’N 13°08.1'.W WS 30. 7.76

— 50°19.3’N —_13°06.9"W

WS02 2498 287 50°19.3’N 12°55.8'W WS 30. 7.76

— 50°20.0'N 12°56.0"W

CP10 4823 2 48°25.5’N 15°10.7'W CP 31. 7.76

— 48°26.3'N 15°09.8"W

WS03 4829 1 48°19.2’N 15°23.3'W WS 1. 8.76

(broken valve) — 48°19.1’N 15°22.5'W

WS07 4281 5 4730!6N 9°372W WS) 72 8.76

— 47°31.2'N —-9°35.7"W

DS14 4254-1 47°32.6’N 9°35.7'W DS_ 7. 8.76

4307 — 47°32.9'N —-9°35.1"W

OS06 4316- 2 46°27.3’N 9°36.2,;W OS 9. 8.76

4307 — 47°27.9'N —_-9°36.0"W.

DS16 4268 7 47°29.8'N 9°33.4';W DS _ 9. 8.76

— 47°30.3'N

QS07 4249 2 47°36.8’N 9°34.3'W OS 10. 8.76

— 47°31.3'N —-9°34.3"W

QS08 4327 AT e29. 8 NI 9392 WS OS eile 85716

— 47°29.5'N —-9°38.8’W.

NORTH AMERICA BASIN

AtlantisII 62 2496 25 39°26.0'N 70°33.0'W ET 21. 8.64

12 64 2886 80 38°46.0'N 70°06.0'W ET 21. 8.64

72 2864 120 38°16.0'N

73 1330- 1 39°46.5'N

71°47.0'W ET 24. 8.64

70°43.3'W ET 25. 8.64

67°57.8'W ET 29. 6.65

69°18.7'W ET 30. 6.65

692OL2OW ET reg 265

70°40.8'W ET 6. 7.65

66°47.0'W ET 24. 8.66

Chain SO 76 28625 53) 39383N

78 3828 3 38°00.8'N

85) 38345 32) 37/59 22N

87 1102 17 39°48.7'N

AtlantisII 126 3806 14 39°37.0'N

24 — 39°37.5'N 66°44.0'W

Chain 106 334 4400 5 40°42.6’N 46°13.8’'W ES 30. 8.72

— 40°44.0'N 46°14.6'W

335 3882— 12 40°25.3’N 46°30.0'W ES 31. 8.72

3919

Knorr 35 340 3264- 95 38°14.4’N 70°20.3'W ES 24.22.73

3356 — 38°17.6'N —_70°22.8’W

We have examined the Verrill & Bush material housed in

the U.S. National Museum. With the exception of specimen

No. 49390, which is more inflated and slightly more inequilat-

eral than is typical of specimens of Y. inconspicua and which

is probably Y. frigida, the Verrill & Bush collection is

correctly described.

Warén (1989) synonymizes Y. inconspicua with Y. nana.

We disagree with this view. Y. nana is essentially a high

latitude species from the shelf and upper slope while Y.

inconspicua s.s. is restricted to temperate latitudes at lower

slope to abyssal depths in the North American and West

European Basins.

Depth range: 1102-4829 m, but most common between

2400-3000 m.

SHELL DESCRIPTION (Fig. 61). The shell is very well

described by Verrill & Bush (1898). We would add that

although the shell is small, compressed and an ovate wedge-

shape, the width, height and thickness of shell for any given

length is variable (Fig. 62). Some specimens have a slightly

sinuous postero-ventral margin. In many specimens the gut

and internal organs are visible through a transparent shell, in

others light and dark banding patterns are present on thicker

shells. Hydroids may be present over most of the shell

margin. The large elongate, slightly ‘saddle-shaped’, internal

ligament is characteristic. The hinge teeth are small, the total

number ranges from 6 in an individual 2.42 mm in length to

13 in an individual of 3.44 mm in length. There is normally an

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 61 Yoldiella inconspicua inconspicua. Lateral views of shells

from the right side and detail of hinge from a right valve; a,

variation in shape of three specimens from Sta. 76 North America

Basin with b, a specimen from Sta. INCAL CP 06 West European

Basin. (Scale = 1.0 mm).

additional tooth in the anterior series (3/3—7/6). Although the

shape varies between individuals there is an overall trend of a

slight increase in posterior umbonal length and in width with

increasing shell length. The height ratio remains more or less

constant (Fig. 62). Analysis of shell length of two samples

from the east and west Atlantic showed marked size differ-

ences (Fig. 64) probably indicative of the differences in time

of successful settlements. Individual peaks in the sample from

the Bay of Biscay perhaps might indicate an annual breeding

event and a lifespan of 5 or 6 years.

Shell measurements (mm) & ratios are as follows:-

Length Height Width H/L W/L PETE

4.20 2.87 1.66 0.68 0.39 0.53

4.03 2.78 1.54 0.69 0.38 0.51

Sh) 2.71 1.53 0.71 0.40 0.50

3.66 2.45 1.43 0.66 0.39 0.53

3.58 2.50 1.38 0.70 0.38 0.50

3.41 Dell - 0.72 9.53

1.49 1.02 0.54 0.69 0.36 0.48

0.99 0.76 = 0.77 - 0.48

0.93 0.62 - 0.67 - 0.50

INTERNAL MORPHOLOGY (Fig. 63). The morphology of the

mantle is essentially the same as in other nuculanoid species.

There are typically three mantle lobes. Specialization of the

mantle margin includes an anterior sense organ, in position

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Length(mm)

Fig. 62 Yoldiella inconspicua inconspicua. Variation in the ratios

of height H/L, width W/L and postero-umbonal length PL/TL to

length against length of a sample from Sta. INCAL CP 08 West

European Basin.

vertically below the anterior adductor muscle. A large sipho-

nal tentacle is usually attached on the right side of the

innermost wall of the siphonal embayment, but was recorded

on the left in a few specimens. Siphons are combined and

form a wide tube with a single lumen. The feeding aperture is

not particularly well-developed, being represented in Y.

inconspicua by two small flaps ventral to the combined

siphon. The inner muscular layer is not expanded anterior to

these, as it is in some other Yoldiella species. The adductor

muscles are large and approximately equal in size. The

posterior muscle is circular and the anterior more ‘crescent-

shaped’.

The gills are well-developed and filaments number from

Fig. 63 Yoldiella inconspicua inconspicua. Lateral view from the

right side of the internal morphology of a specimen from Sta. 72,

North Atlantic Basin. (Scale = 1.0 mm). For identification of the

parts see Fig. 34.

Numbers

1 2

Length (mm)

Fig. 64 Yoldiella inconspicua inconspicua. Length frequency

histograms of two samples from a, Sta. 72 North America Basin

and b, Sta. INCAL CP 08 West European Basin.

12-23, the latter in a large individual 3.55 mm in length. The

distal gill filaments lie close to the siphon and the gill axis

attaches to the siphon ventro-laterally. The labial palps are

moderately large with between 12-22 ridges on the internal

face. The palp proboscides are long and thin. The cerebral

ganglia are large, the visceral ganglia are moderate in size and

the pedal ganglia are large and elongate oval in shape. They

lie more dorsal in position in the foot than in most other

Yoldiella species. The foot is divided and fringed with papil-

lae and has a large byssal gland in the heel.

The oesophagus is distended and wide in diameter. The

longitudinal plane of the stomach lies at an angle to the

vertical sagittal plane, and anteriorly is displaced to the right

while posteriorly it lies to the left. The stomach is large but

somewhat laterally flattened. The style sac is small. The first

section of the hind gut which lies within the foot is wide in

section from thence it curves dorsally parallel to the posterior

margin of the foot. At its dorsal limit of its course there are

two small kinks to the left of the body (possibly a result of

contraction in preserved specimens) before it crosses to the

right side to form a single anterior loop the outline of which is

characteristic of the species. The diameter of the gut appears

to vary somewhat between populations, western Atlantic

specimens appear to have a more slender hindgut although

the dimensions fall within the overall range of eastern Atlan-

tic specimens. A typhlosole is present along the whole length

of the gut. A considerable amount of food material is

frequently present in the left hand digestive diverticulum.

The digestive diverticula extend well posterior within the

body. A large well-developed kidney extends anteriorly close

to the posterior limit of the diverticula.

The sexes are separate. The gonads lie dorsal and ventral

to the viscera and anteriorly they occur internal to the

digestive diverticula. A female 2.8 mm in length collected in

July (Incal CP 07) contained 255 closely packed ova with a

maximum diameter of 132 wm.

Yoldiella inconspicua africana (new subspecies)

TYPE LOCALITY. R.V. Atlantis II, Cruise 42, Sta. 201,

Angola Basin, 23.5.1968, 9°25’S, 11°35’E to 9°29’S, 11°34’E,

Epibenthic Trawl, 1964 m.

TYPE SPECIMEN. Holotype BM(NH) 1992039, Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

SIERRA LEONE BASIN

AtlantisIT 145 2185 29 10°36.0’N 17°49.0'W ES 6.2.67

31 147 3984 5 10°38.0'N 17°52.0'W ES 6.2.67

CAPE BASIN

AtlantisIf 192 2117— 55 23°02.5’'S 12°19.0'E ET 17.5.68

42 2154

194 2864 28 22°54.0'S 11°55.0'E ET 17.5.68

ANGOLA BASIN

ZO 1964 1099 25:0'S 35) 00 Ele 2555508

— 9°29.0'S 11°34.0'E

CAPE VERDE BASIN

Discovery 8521' 3058- 2 20°46.9'N 18°53.4'W WS _ 25.6.74

3053 — 20°47.6'N — 18°53.5'W

8521° 3070-1 =20°47.9'N__18°53.4'°W WS 26.6.74

3964 — 20°48.6'N — 18°53.4"W

8521' 3113— 34 13°47.8'N 18°14.0'W WS 4.7.74

3119 — 13°48.0'N 18°14.8'W

8532° 2958- 12 13°48.2'N 18°08.0'W WS _ 5.7.74

2952 — 13°47.6'N 18°07.5'W

Walda DS20 2514 5 2°32.0'S 8°18.1'W DS

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 65 Yoldiella inconspicua africana.

Outlines a, of a shell from the right side

and a left valve to show detail of the

hinge-plate from Sta. 8532° Cape Verde

Basin and b, two shells from the right

side from Sta. 201 Angola Basin. (Scale

= 1.0 mm).

Y. inconspicua africana is found off the West coast of Africa

in the Sierra Leone, Cape Verde, Angola and Cape Basins at

lower slope to abyssal depths. Depth range: 1964-3119 m.

SHELL DESCRIPTION (Fig. 65). Shell very small, short, rela-

tively compressed, ovate wedge-shape, very slightly inequi-

lateral, except for some very fine lines shell surface smooth,

periostracum pale yellow, iridescent; umbos just anterior to

midline, slightly raised; antero-dorsal margin slightly convex,

nearly horizontal close to umbos, then curving to slightly

pointed anterior margin, ventral margin broadly rounded,

often slightly swollen posteriorly, ascending steeply to poste-

rior supramedial angle, postero-dorsal margin nearly hori-

zontal close to umbo, then slightly convex, sloping gradually

to posterior margin; posterior hinge plate narrow; teeth

small, oblique v-shape, 4-5 on each hinge plate; ligament

short, amphidetic, relatively wide, yoke-shaped, slight exter-

nal extension on either side of umbo.

Prodissoconch length: 166 »m. Maximum recorded shell

length 2.56 mm (Discovery Sta. 8521”).

INTERNAL MORPHOLOGY (Fig. 66). The siphons are com-

bined but with a single lumen. The combined siphon is large

and long, with relatively thin muscular walls. The single

tentacle is large, attached to the right or the left at the base of

the siphonal embayment. The feeding aperture is moderately

well-developed with a small internal secondary fold. The

mantle epithelial in the area of the feeding aperture and

anterior to it is well supplied with gland cells, similar to those

present in Yoldiella curta (p. 47). The anterior sense organ

lies far anterior and is covered dorsally by an extended and

particularly well-developed hood derived from the middle

sensory lobe. The adductor muscles are slightly unequal in

size; the larger anterior muscle is bean-shaped and the

posterior is round in outline. The gills are well-developed

with up to 12 filaments. The labial palps are relatively large

with up to 15 broad ridges on the inner face. The palps extend

across approximately one third of the body. The palp probos-

cides are long and relatively slender. The foot is well-

developed with a deeply divided sole. The byssal gland is

moderately small. The ganglia are large. Both cerebral and

DEEP-SEA PROTOBRANCHIA (BIVALVIA) 45

Fig. 66 Yoldiella inconspicua africana. Lateral view from the right

side of the internal morphology of a specimen from Sta. 8532°

Cape Verde Basin. (Scale = 1.0 mm). For identification of parts

see Fig. 12.

Fig. 67 Yoldiella inconspicua profundorum. Lateral view of shell

from the right side and detail of the hinge-plate of a left valve.

Specimens from Sta. 242 Argentine Basin. (Scale = 1.0 mm).

visceral ganglia are ‘club’-shaped, the visceral being the Yoldiella inconspicua profundorum (new subspecies)

larger. The ovoid pedal ganglia lie central in the foot, just

dorsal and anterior to the byssal gland. A large statocyst lies

Peete th cedal'canslion. : mw" Argentine Basin, 24.3.1971, 37°40.9’S, _51°19.3'W,

The mouth is set posterior to the anterior adductor muscle. Epibenthic Trawl, 3906-3917 m.

The oesophagus is relatively narrow while the stomach is TYPE SPECIMEN. Holotype: BM(NH) 1992038, Paratypes: in

TYPE LOCALITY. R.V. Atlantis II, Cruise 60, Sta. 256,

large with a small style sac which does not penetrate the foot. collection held by J.A. Allen.

The duct of the right digestive diverticulum passes dorsally

around the hind gut to join the stomach close to the oesoph- MATERIAL.

ageal aperture. One of the two left diverticula opens ventral

to the gastric tooth while the second opens adjacent to that ee Sta. Depth No. Lat wae Gea Dae

from the right. No ingested material was observed in the (m)

diverticula. From the style sac, the hind gut passes between

the pedal ganglia and the byssal gland before turning dor-

sally. It makes a very small flexure on the left side immedi- eT SN tN et

AtlantisII 242 4382—- 50 38°16.9'S 51°56.1'W ES 13.3.71

ately before crossing to the right side at the dorsal limit of the 60 4402

body posterior to the ligament. On the right side of the body 243 3815- 1 37°36.8’S 52°23.6°W ES 14.3.71

the hind gut makes a broad sweeping loop as far as the 3822

posterior face of the anterior adductor before passing dorsally 245 2707 2 36°55.7’'S 53°01.4’;W ES 14.3.71

and posteriorly to the anus. 247 5208- 1 43°33.0'S 48°58.1'W ES 17.3.71

Th i i and dorso-l ves

x Ee Daeg ne eee nee rae fa 5° ee 252 4435 23 38°29.8S 52°09.1'W ES 22.3.71

sides of the viscera and extend antero-dorsally with part lying 256 3906- 19 37°40.9’S 51°19.3’W ES 243.71

centrally between the digestive diverticula. The kidney is 3917

small in comparison to the other species of Yoldiella 259-—-3305—, 5 37°13.3'S. 52°45.0°W “ES. 2633.71

described here, extending no further than the posterior edge 3317

of stomach. The heart is relatively large. 264 2041-6 = 36°12.7'S_52°42.7'W ES 28.3.7]

This subspecies differs from Y. inconspicua s.s. in having a a

more elongate outline and a more pointed posterior shell CLS <<

margin. The dorsal margin is slightly more convex, the Restricted to the Argentine Basin at lower slope and abyssal

height/length ratio is slightly greater. The hind gut differs | depths. Depth range: 2041-5223 m.

slightly in the course taken to the right of the body (Figs. 60 &

66). SHELL DESCRIPTION (Fig. 67). Shell small, equilateral, mod-

erately inflated, subovate, fine concentric lines; umbos

slightly raised, inwardly directed; shell outline somewhat

variable, anterior and posterior dorsal margins straight proxi-

mal to umbo, curve distally to broadly rounded anterior and

slightly pointed posterior margins, ventral margin smooth

curve; anterior and posterior hinge plates relatively narrow

Fig. 68 Yoldiella inconspicua profundorum. Lateral view from the

right side of the internal morphology of a specimen from Sta. 242

Argentine Basin. (Scale = 1.0 mm). For identification of the parts

see Fig. 34.

(but broader than in Y. inconspicuous s.s.) short, with up to 7

teeth on each side; ligament amphidetic, large, slightly elon-

gate, short external secondary extensions of fused perios-

tracum on either side of umbo.

The shell shape of this subspecies while similar to that of Y.

inconspicua s.s. is slightly more rounded, in particular the

posterior limit of the shell margin is medial instead of

supramedial. The hinge plate is broader and the teeth stron-

ger in Y. 7. profundorum.

Maximum recorded shell length: 3.31 mm.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Shell measurements (mm) & ratios are as follows:-

Length Height Width H/L W/L PUTL

2.90 2.09 1:25 0.72 0.43 0.52

3).3)ll MDDS 1.47 0.68 0.44 0.52

INTERNAL MORPHOLOGY (Fig. 68). Very similar to that of Y.

inconspicua s.s. and Y. argentinea. In Y. i. profundorum, size

for size, the posterior adductor muscle is more elongate than

in Y. inconspicua s.s., the palps are slightly smaller and the

ridges are broader but not as long and slightly fewer in

number (12-14 internal ridges).

Yoldiella argentinensis (new species)

TYPE LOCALITY. R.V. Atlantis II, Cruise 60, Sta. 237,

Argentine Basin, 11.3.1971, 36°32.6’S, 53°23.0°W,

Epibenthic Trawl, 993-1011 m.

TYPE SPECIMEN. presently housed in the Sanders collection,

Woods Hole Oceanographic Institution, Paratypes: in collec-

tion held by J.A. Allen.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

ARGENTINE BASIN

Atlantis II 236 497-518 3 36°27.0’'S 53°31.6'W ES 11.3.71

60 237 =993- 26) 36°32.6'S. 53°23:0) WasESw est

1011

239 1661— 26 36°49.0’S 53°15.4’'W ES 11.3.71

1679

Y. argentinensis has only been recorded from Argentine

Fig. 69 Yoldiella argentinensis.

Lateral view of the shells from the

right side to show variation in shape;

detail of the hinge-plate of a left

valve; dorsal view of a shell.

Specimens from Sta. 237 Argentine

Basin. (Scales = 1.0 mm).

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Basin at shelf slope break and upper slope depths. Depth

range: 497-1679 m.

SHELL DESCRIPTION (Fig. 69). Shell small, subovate,

approximately equilateral, relatively compressed, ‘boat-

shaped’ in outline except for fine concentric lines, smooth,

iridescent; umbos inflated, inwardly directed; anterior and

posterior dorsal margins concave proximal to umbo, distal to

umbo slightly convex, slope gradually to anterior and poste-

rior margins, anterior margin slightly produced, ventral mar-

gin broadly curved, more convex posteriorly to slightly

produced, posterior margin; horizontal axis supramedial;

hinge plate short, teeth small, ‘V’-shaped, proximal teeth

very small, difficult to discern, 6 anterior and 6 posterior in

individual 3.66 mm long; ligament amphidetic, large with

long, narrow, secondary external anterior and posterior

extensions.

Prodissoconch length: 150 wm. Maximum recorded shell

length: 4.03 mm.

The shape of the shell is similar to that of Yoldiella

inconspicua s.s. The main differences include the marked

proximal concavities of the dorsal margin, the more inflated

umbos and detail of the hinge.

INTERNAL MORPHOLOGY (Fig. 70). There is a wide combined

siphon with a single lumen. The siphonal tentactle lies to the

left side of the siphonal embayment. A feeding aperture is

present ventral to the combined siphon. The adductor

muscles are slightly unequal in size, in cross-section the

posterior is broadly oval in outline while the larger anterior

muscle is ‘bean’-shaped.

The foot is well-developed and there is a large byssal gland

in the heel. The gills are well-developed with between 10-17

alternating filaments (the number varying with the size of the

individual). The labial palps are of moderate size, extending

approximately one third across the body with between 10-18

internal ridges. The hind gut forms a single loop on the right

side of the body (Fig. 70).

Yoldiella curta Verrill & Bush 1898

TYPE LOCALITY. North America’ Basin, 40°16.5'N,

67°05.3'W. 1290 fm. Original specimens were taken from the

North America Basin between 41°11.5’N, 66°12.3’W and

Fig. 70 Yoldiella argentinensis. Lateral view from the right side of

the internal morphology of a specimen from Sta. 237 Argentine

Basin. (Scale = 1.0 mm). For identification of the parts see Fig.

34.

39°38'N — 70°22'W by U.S. Fish Commission Steamer Alba-

tross, 5.10.1883, Beam Trawl.

TYPE SPECIMEN. Holotype U.S. Natl. Mus. No. 38457.

Phaseolus ovatus Verrill 1884, p.230.

Yoldia jeffreysi Verrill 1884, p.229; Verrill 1885, p. 576.

Yoldia curta Verrill & Bush 1898, p. 868, pl. 97, Fig. 8;

Warén 1989, p. 244.

Yoldiella miniscula Verrill & Bush 1898, p. 870, pl. 79, Figs.

2, 7; Warén 1989, p. 244, Figs. 14A & B.

Although a very well-defined species in that it is the only

known Yoldiella with the hind gut configuration described

below (p. 51), in its shell shape it is very similar to a number

of other species. We believe that Y. miniscula Verrill & Bush

is synonymous with it, indeed Verrill & Bush (1898) state this

latter very minute species may, with a larger series, prove to

be the young of one of the preceding species they describe.

These latter include Y. inconspicua, Y. pachia, Y. lucida, Y.

iris, Y. inflata, Y. subangulata, Y. lenticula and Y. curta.

Verrill & Bush (1898) were correct in their supposition and

here we illustrate specimens of Y. miniscula to show their

similarity (Fig. 71).

Note. The holotype specimen of Y. miniscula (U.S. Natl. Mus.

No. 38415) is from the same Station as the holotype of Y. curta.

MATERIAL.

Cruise Sta DepthNo Lat Long Gear Date

(m)

WEST EUROPEAN BASIN

La Perle DS06 1

(BiogasI1) DS07 4

DS12 2180 1 47°28.5'N 8°35.5'W DS _ 9. 8.72

DS13' 2165 ~ 15 47°33.7'N» 8:39:9'W -DS 49..8.72

Jean Charcot

(Polygas) DS25 2096 16+6v 44°08.2'N 4°15.7'W DS __ 1.11.72

DS26 2076 2 44°08:2'N > 4°15.0'W “DS 1h9-72

CV10 2108 2v 47°30.7'N 8°40.6'W CV _ 22.10.72

(Biogas II) DS32 2138 4 47°32.2'N 8°05.3'W DS _ 19.4.73

(BiogasIII) DS36 2147 5 47°32.7'N 8365'W DS 24. 8.73

(1 empty 4 dried)

DS38 2138 7+2v 47°32.5'N

DS49 1845 4+4v 44°05.9'N

(Biogas IV) DS52 2006 2+4v 44°06.3'N

DS61 2250 1 » @47334:7'N

DS62 2175 10 47°32.8’N

DS63 2126 19+2v 47°32.8'N

DS64 2156 7+4v 47°29.2'N

8°35.8'W DS 25. 8.73

4°25.6'W DS 1. 9.73

4°22.4'W DS 18. 2.74

8°38.8'W DS 25. 2.74

8°40.0'W DS 26. 2.74

8°35.0'W DS 26. 2.74

8°30.7'W DS 26. 2.74

(Biogas V) CP07 2170 3 44°09.8’N 4°16.4'W CP 21. 6.74

(Biogas VI) DS71 2194. 7 47°34.3'N 8°33.8’W_ DS 20.10.74

DS86 1950 28 44°04.8’N 4°18.7’W__DS_ 31.10.74

DS87 1913. 7 44°05.2’N 4°19.4.W DS 1.11.74

(13+8v)

DS88 1894 5 44°05.2'N 4°15.4;W DS 1.11.74

Jean Charcot CP08 2177 3 = 44°33.2'N.__ 8°38.5'W_ CP 20.10.74

(Biogas VI) CP09 2171 1 47°33.0’'N 8°44.1.W CP 20.10.74

S777 N 10755-.0°W, CRs 1650776

— 57°56.0'N 10°55.0'W

57°58.4'N 10°42.8'W CP 16. 7.76

— 57°57.7'N_ 10°44.6'W

S759 uNe LOSS W. SDSS s74767,

— 57°59.2'N 10°41.3’W

57°58.5'N 10°48.5'W DS 16. 7.76

— 57°58.5'N 10°49.2'W

Jean Charcot CP01 2068- 38

(Incal) 2040

CP02 2091 4

DS01 2091 468

DS02 2081 544

DS05 2503 2 56°28.1’N 11°11.77;W DS _ 18. 7.76

— 56°27.6’N 11°12.0'W

DS06 2494 6 56°26.6’N 11°10.5'W DS _ 18. 7.76

— 56°25.9'N 11°10.7'W

OS01 2634 5 50°14.4’N 13°10.9°W OS 30. 7.76

— 50°15.2’N 13°11.0'W

Sarsia S-65 1922 19 46°15.0'N 4°50.0'W ED 25. 7.67

33/2 1537— 8 43°41.0'N 3°36.0'W AD 13. 7.67

1830

S44 1739 68 43°40'8’N 3°35'2'W ED 16. 7.67

Chain 106 313 1500-106 51°32.2’N 12°35.9'W ES 17. 8.72

1491

316 2173— 91 50°58.7'N 13°01.6';W ES 18. 8.72

2209 — 50°57.7'N 13°01.3"'W

NORTH AMERICA BASIN

AtlantisII 73 1470-699 39°46.5’N 70°43.3'W ET 25. 8.64

12 1330

Chain 50 87 1102 354 39°48.7'N 70°40.8°W ET 6. 7.65

Chain 58 103 2202 303 39°43.6'N 70°37.4;W ET 4. 5.66

AtlantisII 115 2031-249 39°39.2'N 70°24.5'W ET 16. 8.66

24 2051

AtlantisIf 128 1254 8 39°46.5’N 70°45.2’'W ES _ 15.12.66

30 1310, 217859 53 59°88. 5 Ne 70236. 50 Selo. 1266

— 39°39.0'N 70°37.1"W

Chain 88 207 805—- 239 39°51.3'N 70°54.3’W ES 21. 2.69

811 — 39°51.0'N 70°56.4"W

210 2024 4 39°43.0’'N 70°46.0'W ES 22/23.2.69

1064 — 39°43.2'N 70°49.5'W

ARGENTINE BASIN

Atlantis 11 239 1661- 36 36°49.0’'S 53°15.4;W ES 11. 3.71

60 1679

240) 2195= 1 367437478 53710.2'W ES) 23. 3:71

2323

264 2041- 4 36°12.7'S 52°42.77;W ES 28. 3.71

2048

GUYANA BASIN

Knorr 25 293 2456- 49 8°58.0'N 54°04.3’W ES 27. 2.72

1518

295 1000— 25 8°04.2'N 54°21.3’W ES 28. 2.72

1022

SIERRA LEONE BASIN

AtlantisIf 142 1124 45 10°30.0’N 17°51.5'W ES 5. 2.67

31 1796

145 2185 1 = 10°36.0’N 17°49.0'W ES _ 6. 2.67

BRAZIL BASIN

1595 334-1 7°58.0'S 34°22.0'W_ ES 18. 2.67

939

167 943—- 4 7-58:0'S 34°17-0'W ES 2052.67

1007 — 7°50.0'S

169 587 6 8°03.0'S 34°23.0'W ES 21. 2.67

— 8°02.0'S 34°25.0'W

CAPE BASIN

Atlantis II 189 11007496 23°00.0'S 12°45.0'E ES 16. 5.68

42 1014

190 974 7 23°05.0'S 12°45.0'E AD 17. 5.68

979

1 ISAC 2 2850 S10 S221 Bee Sian l/pes.08

1559

Walda DS10 1432 1 184050 S 10563 ES DS

Y. curta is probably the most widely distributed species of

Yoldiella. It occurs throughout the Atlantic at slope and

abyssal rise depths. Depth ranges:

Brazil. Basin yee secceycsscee eevee ohne ene 587-1007 m

Caper Basin: yegassas.cie eto te ee 974-1559 m

Guyana Basint€. 5394. Meet ence ceeenes 1000-1518 m

AT eentine Basimien yn. 25.cesesce-ccme este 1661-2048 m

Sichhasleconey Bs asinwreresseereteneeeeree eee rerere 1624-2185 m

INonthyAmen Canty asinl ieesecceeceereseeereecretr 805-2178 m

WieSi#E uno peanls asin senate rercre-eeecete 1537-2634 m

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

SHELL DESCRIPTION (Figs. 71 & 72). Verrill & Bush (1898)

give a full and accurate description of this species. Y. curta

has a small, smooth, ovate, semi-transparent shell through

which the characteristic, indeed unique, course of the hind

gut is usually visible. The latter is usually seen as a double

strand on the right side of the body with a single loop on the

left extending out from the posterior margin of the anterior

adductor. The hinge is short with a large internal ligament.

The outline of the shell is variable both within (Fig. 73) and

between populations. There is no lunule or escutcheon. The

hinge plate is very short and slender and does not reach to the

level of the inner margin of the adductor muscles. The

number of teeth on each hinge plate varies with size up to a

maximum of 7. There is usually one more tooth on the

posterior hinge plate. The shell may be confused with other

species e.g. Y. inconspicua, Y. lucida and Y. frigida, even

though the hinge and the hind gut configuration are charac-

teristic.

In general, with increasing length, the height/length ratio

increases thus producing a more rounded outline (Figs. 74 &

75). The outlines of the anterior and posterior margins are

variable. The anterior margin may be smoothly rounded or

slightly angular, while the posterior margin is slightly

extended with the degree of curvature and the position of the

posterior limit in relation to the mid horizontal shell axis

somewhat variable. With increasing size shells become more

inequilateral with the posterior end slightly elongate. There is

also a gradual increase in the width to length ratio.

Prodissoconch length: 170 ~m. Maximum recorded shell

length: 4.77 mm.

INTERNAL MORPHOLOGY (Figs. 76 a & b). As in other

Yoldiella species the mantle is little modified and for the most

part unfused. The inner muscular lobe is relatively broad and

somewhat folded in preserved specimens. Posteriorly the

inner muscular layer fuses to form a relatively wide, thin-

walled combined siphon with a single lumen. In one whole

mount several faecal pellets lying one on top of the other

were seen within the siphon and in one series of sections two

faecal pellets one in the dorsal half and one in the ventral half

of the siphonal lumen were seen. The gill axes attach laterally

close to the ventral margin of the siphon, thus any inhalent

componant is probably restricted to the ventral margin. A

large siphonal tentacle originates from a pocket in the sipho-

nal embayment at the base of the siphon, usually on the left

side. A small secondary muscular mantle fold marks the inner

limit of the feeding aperture which in life must extend beyond

the shell margin as a pair of flaps. Here the inner mantle lobe

is increased in thickness and width and in the preserved

contracted state is much folded. The epithelium on the

ventral side of the secondary muscular fold, on the dorsal side

of the muscular fold, as well as the epithelium between the

two, is well supplied with acidophilic gland cells. The gland

cells within the epithelium between the folds extend anteri-

orly beyond the limit of the feeding aperture for a short

distance. The anterior sense organ is well-developed. Over it

the middle sensory lobe forms a long thin flap which is

well-supplied with glandular epithelial cells. The adductor

muscles are large, approximately equal in size with the ‘quick’

and ‘catch’ parts clearly visible. The anterior adductor if

anything is slightly the larger, it is ‘“crescent’-shaped in cross

section while the posterior muscle is approximately circular.

The gills lie comparatively ventral in position within the

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

mantle cavity. The outer and inner demibranchs are attached

to the mantle and body respectively by tissue junctions.

Depending on the size of the individual there are 11-16

alternating gill plates. The labial palps are moderately large,

extending approximately 1/3 across the body and have

between 13-19 wide ridges on their inner faces.

The foot is large and well-developed. A large byssal gland

is present, with little obvious internal structure as seen in

whole mounts. At the point where the gland opens to the

exterior the surrounding tissue contains acidophilic gland and

basiphilic cells. As in other species of Yoldiella there is a

broad band of posterior retractor muscles. The latero-

posterior retractor muscle is inserted ventrally on lateral body

wall. There are three major pairs of anterior pedal retractor

muscles which, from the neck of the foot, pass to either side

of the oesophagus and insert on the shell posterior to the

anterior adductor muscle. Another smaller pair of anterior

retractor muscles insert immediately posterior to the anterior

adductor and pass within the ventral visceral margin at

epithelia to the region of the mouth (Fig. 76b). Posterior to

these a second pair of muscles pass vertically from the dorsal

shell margin to the labial palps.

The cerebral ganglia are relatively large, as are the

elongate-oval pedal ganglia. The visceral ganglia are smaller,

cylindrical and lie close to the antero-ventral margin of the

posterior adductor muscle.

The mouth is a short distance posterior to the anterior

adductor muscle. The oesophagus curves dorsally and anteri-

orly before turning posteriorly to enter the stomach approxi-

mately midway on the left side of the anterior face. No

sorting ridges are visible externally on the right side of the

stomach. There is a prominent gastric tooth at the left

antero-dorsal edge of the gastric shield. The latter extends

posteriorly over the left, the dorsal and part of the right wall.

The style sac is small, narrow and penetrates the foot to level

of pedal ganglia. The digestive diverticula are extensive

occurring on the right and left sides of the body and anterior

to the stomch. Fine material was observed in the lumen of the

left digestive diverticulum. A duct from the left side opens

into the stomach below the gastric tooth. The course of the

two other ducts are less clear, but from the evidence of other

species they probably open into the stomach anteriorly close

to the oesophagus. The hind gut sweeps across the ventral

Fig. 71 Yoldiella

curta. a, lateral

external and

internal view of

left valve of the

type specimen of

Y. curta (USNM

No.38457) and b,

the lateral

external and

internal view of

the right valve of

the type specimen

of Y. miniscula

(USNM No.

38415). Specimens

from the U.S. Fish

Commission Sta.

2084 North

America Basin.

(Scale = 1.0 mm).

Fig. 72 Yoldiella curta. a, lateral view from right side of shell,

detail of the hinge-plate of a right valve and dorsal view of a shell

from U.S. Fish Commission Sta. 2073 North America Basin,

compared with b, a lateral view of a shell from the left side and

detail of the hinge-plate of a right valve from Sta. Polygas DS 25

West European Basin. (Scale = 1.0 mm).

right side of the viscera to the anterior adductor muscle,

where it crosses to the left side of the body to form a single

loop before returning to the right alongside the outward

Fig. 73 Yoldiella curta. Outlines of shells of a similar size to show

intrapopulation differences in shape. Specimens from Sta. BG IV

DS 86 West European Bain. (Scale = 1.0 mm).

W/L © ‘olan e e ce ss e 0

. oe “oat” ee

Length (mm)

Fig. 74 Yoldiella curta. Variation in the ratios of height H/L, width

W/L and postero-umbonal length PL/TL to length against length

of a sample from Sta. INCAL CP 01 West European Basin.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 75 Yoldiella curta. Outlines of shells from the right side to

show change in shape with growth. Specimens from Sta. BG I DS

13 West European Basin. (Scale = 1.0 mm).

section of the mid dorsal margin of the body and from there

to the anus. A shallow typhlosole is present along the length

of the hind gut. Occasional aberrent specimens were

recorded with an extra length of gut being accommodated

within the general pattern (see Fig. 75).

The kidney is well-developed. There is a large pericardial

cavity but the heart is relatively small with few muscle fibres

in the wall of the ventricle. Gonads occur dorsally from the

anterior adductor muscle to just posterior to the stomach and

in the anterior part of the body internal to the digestive

diverticula and hind gut. The sexes are separate. In one

sectioned female (2.3 mm) 27 ova were counted and in other

specimens (1.8 and 2.1 mm) 69 and 70 ova were recorded.

respectively. The maximum dimension was 108 pm.

This is one of a few deep-water specimens which were

brought to the surface alive and from which it was posible to

make some observations on the ciliary currents of the mantle

and the contained organs. The ciliary sorting mechanisms of

the gills, palps, mantle and body were found to be similar to

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

those described by Stasek (1965) for Yoldia ensifera.

The ciliation on the frontal surface of the gill plates is

axially directed, there those on the posterior 2/3rds of the axis

move anteriorly and those on the anterior 1/3rd move poste-

riorly. Particles thus accumulate at a point which is close to

where the palp proboscides join the dorsal palp surface and

they are accepted onto the palp. The palp ridges sort in the

manner described by Stasek (1965). Rejected particles arrive

at the posterior-ventral margin of the palp. A main rejection

tract at the mantle edge to the inside of the muscular fold

carries these particles to a point of collection at the ventral

edge of the feeding aperture. Particles on the body eventually

pass to the dorsal margin of the palps and join with those

from the gills.

Hydroids were present on the shell margins of a number of

specimens.

Yoldiella perplexa (new species)

TYPE LOCALITY. R.V. Knorr Sta. 299, Guyana Basin,

29.2.1972, 7°55.1’N, 54°42.0’W, Epibenthic Trawl,

1912-2076 m.

TYPE SPECIMEN. Holotype BM(NH) 1992031, Paratypes: in

collection held by J.A. Allen.

Fig. 76 Yoldiella curta. Lateral views from the right and left sides

of the internal morphology of a specimen from Sta. BG VI DS 71

West European Basin. (Scale = 1.0 mm). For identification of the

parts see Fig. 34.

Fig. 77 Yoldiella perplexa. Lateral view of shell from the right

side, lateral internal view of a right valve to show detail of

hinge-plate and a dorsal view of a shell. Specimens from Sta. 299

Guyana Basin. (Scale = 1.0 mm).

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

GUYANA BASIN

Knorr 25 293 2456- 22 8°58.0'N 54°04.3'W ES 27.2.72

1518

299 1942— 82 7°55.1'N 54°42.0'W ES 29.2.72

2076

Recorded from the lower slope of the Guyana Basin. Depth

range: 1456-2076 m.

SHELL DESCRIPTION (Fig. 77). Shell small, ovate, moderately

inflated, inequilateral, smooth with some fine irregularly

spaced concentric lines at ventral margin, periostracum pale

yellow; umbos moderately developed, slightly raised,

inwardly directed anterior to midline; proximal dorsal margin

straight in small specimens, slightly convex in larger, antero-

dorsal margin curves gradually to wide anterior margin,

dorsal part slightly more convex than ventral, ventral margin

deeply convex, postero-dorsal margin slopes gradually to

steeply rounded posterior margin, postero-ventral margin

relatively straight and in some specimens very slightly sinous;

hinge plate moderately broad, not narrow below umbo, hinge

teeth strong, few in number, 6 anterior and 6 posterior in

individual 2.6 mm; ligament amphidetic, moderate in size,

not extending to ventral edge of hinge plate, round in lateral

Fig. 78 Yoldiella perplexa. Lateral view from the right side of the

internal morphology of a specimen from Sta. 299 Guyana Basin.

(Scale = 1.0 mm). For identification of parts see Fig. 34.

view with little external periostracal extension anterior and

posterior to the umbo.

Prodissoconch length: 177 »m. Maximum recorded shell

length: 3.11 mm.

INTERNAL MORPHOLOGY (Fig. 78). The combined siphons

are well-developed. There is a long thin siphonal tentacle

attached to the left ventral side of a moderately deep siphonal

embayment. The anterior sense organ is well-developed. The

adductor muscles are relatively large; the anterior is bean-

shaped and slightly larger than the posterior and which is

more round.

The gills bear up to 16 alternating plates which are distant

from the internal limit of the siphons and to which they are

joined by long extended axes. The labial palps are relatively

small and extend approximately 1/4 distance across body.

There are up to 13 palp ridges on the inner face. The palp

proboscides are moderately well-developed.

The foot is also well-developed and anterior in position in

preserved specimens. There is a small byssal gland and the

pedal ganglia dorsal to the gland are also small. The visceral

ganglia are slender and elongate while the cerebral ganglia

are slightly larger and more ‘club’-shaped. The stomach and

style sac are large. The hind gut describes a shallow single

loop to the right side of the body. No gonads were seen in the

whole mounts.

Y. perplexa is characterized by a rounded high shell which

has a slightly sinuous postero-ventral shell margin. Unlike

other high rounded species such a Y. americana and Y.

subcircularis it has a simple and not particularly extensive

hind gut loop to the right and thus has characters intermedi-

ate between Y. lucida or Y. obesa and species such as Y.

subcircularis.

Yoldiella americana (new species)

TYPE LOCALITY. R.V. Chain Sta. 84, North America Basin,

4.7.1965, 36°24.4'N, 67°56.0’W, Epibenthic Trawl, 4749 m.

TYPE SPECIMEN. Holotype BM(NH) 1992032, Paratypes: in

collection held by J.A. Allen.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

MATERIAL.

Cruise Sta. Depth No Lat Long Gear Date

(m)

NORTH AMERICA BASIN

AtlantisII 70 4680 190 36°23.0'N 67°58.0'W ET 23. 8.64

Chain 50 77 ~—-3806 1 38°00.7'N 69°16.0'W ET 30. 6.65

80 4970 75 34°49.8'N 66°34.0'W ET 2. 7.65

81 5042 9 34°41.0'N 66°28.0'W ET 2. 7.65

83 5000 4 34°46.5'N 66°30.0'W ET 3. 7.65

84 4749 235 36°24.4'N 67°56.0'W ET 4. 7.65

85 3834 4 37°59.2'N 69°26.2';W ET 5. 7.65

86 3843 268 37°59.0'N

AtlantisII 92 4694 3 36°20.0'N

17 93 5003 6 34°39.0'N

AtlantisII 121 4800 66 35°50.0'N

24 122 4833 25 34°50.0'N

—35752-0'N

123. 4853. 94 37°29.0'N

124 4862 76 37°26.0'N

692185) WETS. ius

67°56.0'W ET 13.12.65

66°26.0'W ET 14.12.65

65°11.0'W ET 21. 8.66

64°57.5'W ET 21. 8.66

64°58.0'W

64°14.0'W ET 22. 9.66

63°59.5'W ET 22. 8.66

— 37°25.0'N 63°58.0'W

125 4825 37 37°24.0'N 65°54.0'W ET 23. 8.66

— 37°26.0'N — 65°50.0"W

AtlantisII 175 4667— 145 36°36.0’N 68°29.0'W ES 29.11.67

40 4693 — 36°36.0'N 68°31.0'W

Chain 106 330 4632 243 50°43.5’N 17°51.7';W ES 24. 8.72

— 50°43.4’N — 17°52.9'W

331 4793 10 41°13.0’N 41°36.7'W ES 29. 8.72

— 41°13.2'N — 41°38.7'W

ARGENTINE BASIN

AtlantisII 242 4382- 8 38°16.9’S

60 4402

247 5208- 293 43°33.0’S

5223

252 4435 3829818

GUYANA BASIN

5156.1 W SESe 15.3270

48°58.1'W ES 17. 3.71

52:09:10 Wi BS 225S7m)

Knorr 25 287 4980- 12 13°16.0’N 54°52.2’W ES 24. 2.72

4034 — 13°15.8'N 54°53.1"W

288 4417— 45 11°02.2'N 55°05.5'W ES 25. 2.72

4429 — 11°03.8'N 55°04.8"W

Biovema DS03 5150 3 10°47.1'N 42°40.77;W DS 16.11.77

— 10°47.1'N 42°40.3"W

DSO5 5100 =28 =10°45.9'N 42°40.2.;W_ DS _ 18.11.77

— 10°46.8'N 42°39.8'W

CO04 5100 1 10°45.9'N 42°40.2".W CP 18.11.77

— 10°45.9'N 42°39.3"W

DS09 5875 Lis JIS36:SIN. 432-51. 8aW DS 25 77

— 11°37.1'N 32°51.3’W

DS11 5867 2 11°37.5'N 32°43.8'W DS 26.11.77

— 11°37.6'N —32°52.8"W

SIERRA LEONE BASIN

Atlantis II 139 2099- 1 10°33.0’'N 17°53.0’'W ES 4. 2.62

31 2187

Y. americana is found mainly in the deep western Atlantic

with a few records to east of the Atlantic Ridge at the western

edge of the Sierra Leone Basin. Otherwise the species is

recorded from the North America, Guyana and Argentine

Basins. Depth range: 2099-5867 m.

SHELL DESCRIPTION (Fig. 79). Shell small, ovate, moderately

inflated, approximately equilateral; umbos moderately

raised, inwardly directed; dorsal margin slightly convex,

antero-dorsal margin slopes evenly to join broad curve of

anterior margin, ventral margin more convex posteriorly,

DEEP-SEA PROTOBRANCHIA (BIVALVIA) 53

rior external extension of fused periostracum.

Prodissoconch length: 187 wm. Maximum recorded shell

length: 2.5 mm.

There is little change in the posterior umbonal length/total

length ratio or the height/length ratio with increasing size,

however, individuals tend to become more tumid with

increasing length. The width/length ratio is the most variable

feature when comparing populations from different areas

(Fig. 80). Thus, specimens from the west Atlantic are rela-

tively wider than those from the the east Atlantic although in

lateral view (Fig. 81) and in internal anatomy they differ

little. Populations are remarkably different in their size

range. This is probably indicative of single massive successful

spatfalls at different times (Fig. 82).

INTERNAL MORPHOLOGY (Fig. 83). The anterior sense organ

is moderately well-developed. The siphons are combined,

with the inhalent siphon open at the ventral edge. A siphonal

tentacle originates from the base of the siphonal embayment,

either on the right or the left side. There is a feeding aperture

ventral to the siphons. Anterior to this the inner muscular

lobe is enlarged convoluted and heavily ciliated. The adduc-

Fig. 79 Yoldiella americana. Lateral view of shell from the right

side, lateral internal view of a left valve, enlarged view of a

hinge-plate of a left valve and a dorsal view of the shells.

Specimens from Sta. 80, North America Basin. (Scale = 1.0 mm).

50 Fase a

i es

Length (mm)

Fig. 80 Yoldiella americana. Variation in ratio of height H/L,

width W/L and postero-umbonal length PL/TL to length against

length of subsamples from Sta. Biovema DS 05, Cape Verde

Basin (closed circles) and from Sta. 247 Argentine Basin (open

triangles).

Créleiere

posterior margin rounded or with slight angulation forming

slight subrostrum; hinge plate moderately strong, long strong Fig. 81 Yoldiella americana. Outlines of shells from the right side

chevron-shaped teeth, equal numbers on anterior and poste- to show change in shape with growth of specimens from Sta.

rior plates, 14/14 in a specimen 2.44 mm total length; Biovema DS 05 Cape Verde Basin (left) compared with

ligament amphidetic, small, rectangular in shape, small poste- specimens from Sta. 247 Argentine Basin. (Scale = 1.0 mm).

tor muscles are relatively small and elongate and approxi-

mately equal in size. The gills are well-developed. The exact

number of gill plates is difficult to determine but at least 16

are present in the largest specimen. The labial palps are

relatively large with up to 17 ridges on the inner face and with

long palp proboscides. The foot is elongate with a relatively

narrow neck. Many subepithelial gland cells open on to the

sole of the foot. There is a relatively large byssal gland in the

heel. A small papilla is present immediately posterior to the

aperture of the byssal gland. The cerebral and visceral ganglia

are ‘club’-shaped and of moderate size. The pedal ganglia, in

the neck of the foot, are large and elongate.

The hind gut passes from the style sac to the /eft side of the

body and forms a loop then crosses to the right side where it

forms a similar loop before passing postero-dorsally to the

anus. The point of crossover from left to right is ventral to the

ligament or slightly posterior to it. A small typhlosole is

present along the length of the gut.

The sexes are separate. From whole mounts, it appears

that the ovaries contain relatively few large ova. The testes

occupy a large part of the anterior half of the body with the

digestive diverticula dorsal to them.

Y. americana has a similar rounded shape to Y. perplexa

although without the slight sinuous postero-ventral margin of

the latter species. Y. americana is the only species taken with

a single hind gut loop to the right and left of the body.

Yoldiella subcircularis (Odhner 1960)

Portlandia (Yoldiella) subcircularis Odhner 1960, p. 369, pl.

L Rigel.

TYPE LOCALITY. Swedish Deep-Sea Expedition, Sta. 373,

North America Basin, collected by R.V. Albatross,

24.8.1948, 28°25'N, 61°05’'W — 28°05’N, 60°49'W,

5,500-5,987 m.

3 40

1 2

Length(mm)

Fig. 82 Yoldiella americana. Length frequency histogram of a

sample from Sta. 84, North America Basin.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 83 Yoldiella americana. Lateral views from right and left sides

of the internal morphology of a specimen from Sta. 84, North

America Basin. (Scale = 1.0 mm). For identification of parts see

Fig. 34.

TYPE SPECIMEN. Holotype: Swedish Museum of Natural His-

tory, Stockholm.

MATERIAL.

Cruise Sta DepthNo Lat Long Gear Date

(m)

WEST EUROPEAN BASIN

Jean Charcot DS20 4226 7 47°33.0'N 9°36.7'W DS_ 24.10.72

(Polygas) DS21 4190 1 47°31.5'N 9°40'7'W_ DS_ 24.10.72

DS22 4144 4 47°34.1'N 9°38.4'W DS 25.10.72

(Biogas IV) DS54 4659 2 46°31.1'N 10°29.2’W DS 21. 2.74

DSS55 4125. 7 47°34.9'N 9°40.9'W DS 22. 2.74

(Biogas V) S68 4550 1 46°26.7'N 10°23.9'W DS 19. 6.74

9°07.8'W DS 22.10.74

9°33.3'W DS 23.10.74

9°34.6'W DS 24.10.74

(Biogas VI) DS75 3250 1 47°28.1'N

DS76 4228 29+1v 47°34.8'N

DS77 4240 13+2v 47°31.8'N

DS78 4706 4 46°31.2'N 10°23.8’W DS 25.10.74

DS79 4715 13 46°30.4'N 10°27.1'W DS 26.10.74

DS80 4720 4 46°29.5'N 10°29.5'W DS 27.10.74

DS81 4715 1 46°28.3'N 10°24.6'W DS 27.10.74

Jean Charcot QS02 4829 2 48°19.2'N 15°15.7'W OS _ 2. 8.76

(Incal) QS05 4296- 1 47°31.3'N 9°34.6'W OS 7. 8.76

4248 — 47°32.2'N 9°34.7'W

QS06 4316 6 46°27.3'N 9°36.2'W OS 9. 8.76

— 47°27.9'N —_9°36.0’W

QS07 4249 15 47°31.8’N 9°34.3'W OS 10.8.76

— 47°31.3'N 9°34.3’W

QS08 4327 5 47°29.8'N 9°39.2'W OS 11. 8.76

— 47°29.5'N 9°38.8'W

WS03 4829 10 48°19.2'N 15°23.3'W WS | 1. 8.76

— 48°19.1'N 15°22.5'W

WS07 4281 4 47°30.6'N 9°37.1'W WS _ 7. 8.76

— 47°31.2'N 9°35.7'W

WS08 4287 11 47°30.5'N 9°33.7'W WS 9. 8.76

WS09 4277 _ 3 47°28.8'N 9°34.0'W WS 10. 8.76

— 47°27.9'N

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

WS10 4354 10 47°27.3'N

— 47°18.2'N

Jean Charcot DS11 4823 1 48°18.8'N

(Incal) — 48°18.6'N

DS14 4254— 3 47°32.6'N

4248 — 47°32.6'N

DS15 4268 12+2v 47°29.8'N

— 47°30.3'N

CP11 4823 1 48°20.4'N

— 48°21.2'’N

Chain 106 330 4632 8 50°43.5'N

— 50°43.4'N

CANARIES BASIN

Discovery 6714 3301 3 27°13.0'N

GUYANA BASIN ;

Knorr 25 287 4980- 5 13°16.0'N

4934

288 4417-64 11°02.2'N

4429

Jean Charcot DS03 5150 1 10°47.1'N

(Biovema) — 10°47.1'N

DS05 5100 6 10°45.9'N

— 10°46.0'N

CP04 5100 1 10°45.9'N

— 10°45.9'N

CAPE BASIN

Jean Charcot DSO5 4560 3 55°20'5'S

(Walvis) DS06 4585 7 33°24.5'S

DS07 5100 20 26°59.7'S

DS08 5225 3 26°59.6'S

DS09 5220 15 26°59.9'S

NORTH AMERICA BASIN

AtlantisI] 70 4680 1 36°23.0'N

Chain 50 iow 8828 2 38°00.0'N

80 4970 45 34°49.8'N

81 5042 14 34°41.0'N

83 5000 2 34°46.5'N

85. 385418 37°59.2'N

AtlantisII 92 4694 3 36°20.0'N

AtlantisII 93 5007 23 34°39.0'N

24 121 4800 2 35°50.0'N

AtlantisII 175 4667— 2 36°36.0'N

40 4693

9°39.9'W

15°11.5'W

15°12.0’W

O57 WV.

9°35.1'W

9°33.4'W

15°14.6'W

15°13.7'W

51°07.0'W

51°09.0'W

15°41.0'W

54°52.2'W

55°05.5'W

42°40.7'W

42°40.3'W

42°40.2'W

42°39.8'W

42°40.2'W

42°39.3'W

2°34.0'E

2°32.0'W

1°07.1'E

1°07.3'E

1°06.7'E

67°58.9'W

69°18.7'W

66°34.0'W

66°28.0'W

66°30.0'W

69°26.2'W

67°56.0'W

66°26.0'W

65°11.0'W

68°29.0'W

. 8.76

. 8.72

. 3.68

we 2

SPRAY)

16.11.77

18.11.77

30.12.78

31.12.78

23.

179

L379

8.64

. 6.65

7.65

eas)

7.65

13.12.65

14.12.65

8.66

29.11.67

This is a true abyssal species found only in the deepest part of

the Basins and, except for the Argentine & Norwegian Basins

is widely distributed throughout the Atlantic. Depth range:

3250-5225 m.

SHELL DESCRIPTION (Figs. 84 & 85). Shell small, moderately

thick, oval, inflated, inequilateral, posterior margin slightly

produced; surface with very fine irregular concentric lines,

fine radial striae present in some specimens, dorsal area

between umbo and posterior margin furrowed; umbos raised

slightly, orthogyrate; dorsal margin proximally straight on

either side of umbo, distally antero-dorsal margin joins

rounded anterior margin in broad curve which continues to

ventral margin, more convex posteriorly, distal postero-

dorsal margin curves more gradually to produce slightly

drawn out posterior margin, limit of posterior margin supra-

medial; hinge plate moderately broad, long, slightly curved,

up to 10 small ‘V’-shaped, chevron teeth on each side of

ligament; ligament amphidetic, small, ‘goblet’-shaped, small

external extension of fused periostracum on either side of

umbo, small chondrophore present.

Prodissoconch length: 146-187 1m. Maximum recorded

shell length 4.4 mm.

The description of Portlandia (Y) subcircularis (Odhner,

1960) agrees well with that presented above.

With increasing length, the posterior part of the shell

becomes slightly more extended and at the same time the

postero-dorsal margin becomes more smoothly curved (Figs.

85 & 86). The width to length ratio also increases with

increasing size, but little proportionate change occurs in the

height to length ratio although this varies in individuals

between 0.72 and 0.84. The height/length ratios are the

highest recorded for any species of Yoldiella. In some larger

specimens the dorsal margin immediately anterior and poste-

rior to the umbos may become slightly concave and as a result

a small, shallow lunule and escutcheon may be formed.

Comparison of specimens from the different Basins show that

northerly (W. European) and southerly (Angola) populations

in the eastern Atlantic are similar in form as too are the North

Fig. 84 Yoldiella subcircularis.

Lateral view of a shell from the

right side and a right valve to show

the detail of the hinge-plate.

Specimens from Sta. 285 Guyana

Basin and Sta. 93 North Atlantic

Basin respectively. (Scale = 1.0

mm).

Fig. 85 Yoldiella subcircularis. Outlines of shells from the right

side to show variation in shape. Specimens taken from Sta. BG

VI DS 76, West European Basin. (Scale = 1.0 mm).

50-4 “. os 1% *s —- 2

{WL =

gue

40- s .

7 o * Somes ctee om Soy”

sold arcs ‘ce es

70- H

60-5 eet sap bs ° a, i nt

>PLITL ’ fhe a e S HF. ry a

50-

SSS en a

1 2 3 4

Length(mm)

Fig. 86 Yoldiella subcircularis. Variation in ratios of height H/L,

width W/L and postero-umbonal length PL/TL to length against

length of subsamples from Sta. BG DS 76, West European Basin

(closed circles) and Sta. Walvis QS 07, Cape Basin (closed

squares).

J,A. ALLEN, H.L. SANDERS AND F. HANNAH

America specimens. In contrast the small number of speci-

mens from the Guyana Basin differ slightly in having a lower

height/length ratio (significant at the 0.1 level).

INTERNAL MORPHOLOGY (Figs. 87 & 88). In Y. subcircularis

the volume of the mantle cavity is large compared with that of

the body. A well-developed sense organ lies at the far

anterior margin. The siphons are combined and the inhalent

siphon is shorter than the exhalent and is open ventrally.

Both siphons are thin-walled and a pair of lateral haemoco-

eles are present in the junction between them. There is a

moderately large siphonal tentacle, most frequently found on

the left side. The feeding aperture is well-developed with

areas of glandular mantle epithelium on each side which are

probably extended in life as paired, broad flaps. For some

distance anterior to these, the inner muscular lobe is particu-

larly well-ciliated and it may be that the feeding area either is

separated from the pedal gape by a ciliary junction or it is the

region where pseudofaeces are formed. The adductor

muscles are small, approximately equal in size, oblong in

shape and lie close to the dorsal and anterior and posterior

mantle margins respectively.

The gill plates are relatively few in number (18 in a

specimen 3.0 mm). Tissue junctions join the demibranchs to

the mantle dorsally. The gill plates are particularly muscular

Fig. 87 Yoldiella subcircularis. Lateral views from right and left

sides of the internal morphology of a specimen from Sta. 80 North

America Basin. (Scale = 1.0 mm). For identification of parts see

Fig. 34.

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

and well-developed. The labial palps are large, with up to 32

closely spaced ridges on each inner face. In some of the

largest specimens (> 3.3 mm) the anterior part of the palps

are frequently folded in on themselves. The palp proboscides

are relatively small and slender. The foot is conspicuous,

being long and thin, with a much extended narrow neck and a

long divided papillate sole. Gland cells are present along the

ventral part of the sole and surrounding the aperture of a

large byssal gland. Pedal retractor muscles are less conspicu-

ous in this species than in others described here. The central

haemocoele of the foot is extensive. The cerebral and visceral

ganglia are relatively small, circular in transverse vertical

cross-section. The visceral ganglia are some distance anterior

to the posterior adductor muscle. The pedal ganglia lie at the

dorsal limit of the extended neck of the foot close to its

junction with the body, they are large and elongate with large

associated statocysts dorsal to them.

The mouth is displaced a short distance posteriorly from

the anterior adductor muscle. The stomach and style sac are

moderately large. Two broad sorting ridges can be seen on

the right anterior wall of the stomach. A prominent gastric

tooth is present on the left dorsal wall and posterior to it the

gastric shield extends over the left and most of the right walls

of the stomach. The major typhlosole extends along the right

side of the stomach. The digestive diverticula lie either side

and anterior to the stomach. The duct of the right digestive

diverticulum curves dorsally over the hind gut and enters the

stomach on the right anterior dorsal wall. A duct from one

left diverticulum enters the stomach far anterior on the left

dorsal side, and immediately posterior to it, a short duct from

a second left diverticulum enters the stomach, ventral to the

gastric tooth. Material similar to that in the stomach was

‘present in the lumen of the latter diverticulum, but this could

possibly have resulted from tissue contraction following fixa-

tion. The style sac is relatively large and extends into the

dorsal part of the foot. The hind gut has a shallow typhlosole

along its entire length, the impression of which can be seen on

extruded faecal pellets. The hind gut is arranged in two loops

on each side of the body. These are usually visible through

Fig. 88 Yoldiella subcircularis. Dorsal view of the hind gut of a

specimen from Sta. 80 North America Basin and a diagrammatic

view of the course of the hind gut as seen from the left side.

(Scale = 1.0 mm).

the shell antero-dorsally. There is also a double vertical

extension of the hind gut deep into the foot. Thus, design

advantage is taken of the exceptional length of the neck of the

foot to accommodate a significant part of the greatly

extended hind gut.

The sexes are separate. Sectioned specimens larger than

2.8 mm had maturing gonads. The number of ova ranged

from 37 (2.80 mm) to approximately 140 (2.91 mm) with a

maximum ovum diameter of 132 m and 156 um respectively.

The gonads overlie the lateral and dorsal sides of the viscera.

Mature females were present in February, June, August and

October samples from the West European Basin. In two

specimens from (Sta. DS76, Sta. DS79 respectively both 2.91

mm total length), eggs were partially shed into the mantle

cavity and had a maximum dimension of 156 pm. Neverthe-

less, there is no evidence to show that eggs are retained and

incubated within the mantle cavity.

Although the kidney is relatively small, it extends forward

on either side of the stomach for a short distance.

Yoldiella biguttata (new species)

TYPE LOCALITY. R.V. Knorr Cruise 25, Sta. 299,Guyana

Basin, 29.2.1972, 7°55.1'N, 55°42.0’'W, Epibenthic Trawl,

1942-2076 m.

TYPE SPECIMEN. Holotype: BM(NH) 1992029. Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

BRAZIL BASIN

AtlantisI] 167 943- 5S 7°58.0'S 34°17.0'W ES 20.2.67

31 1007 — 7°50.0'S — 34°17.0"'W

ARGENTINE BASIN

Atlantis) 245 "2707 § 2. 36:55.7’S 9 es30l.4°W SES 14:377i

GUYANA BASIN

Knorr 25 293 1456- 13 = 8°58.0’N 54°04.3'W ES) 27.2.72

1518

295 1000- 2 8°04.2’N 54°21.3'W ES 28.2.72

1022

299 1942—- 74 7°55.1'N 55°42.0'W ES 29.2.72

2076

301 2487- 44 8°12.4'N 55°50.2'W ES 29.2.72

2500

303 2849- 4 8°28.8'N 56°04.5'W ES 1. 3.72

1853

Y. biguttata is distributed off the coast of eastern South

America at mid slope to abyssal depths in the Argentine,

Brazil and Guyana Basins. Depth range: 943-2853 m.

SHELL DESCRIPTION (Fig. 89). Shell small, inflated, equilat-

eral, fine concentric striae; umbos posterior to midline,

slightly raised, moderately large, inwardly directed; dorsal

margin raised, sharp-edged, particularly so anterior to umbo,

dorsal margin close to umbo straight, proximal antero-dorsal

margin curves to broadly rounded anterior margin, the limit

of which is slightly ventral to the midline, ventral margin

shallow curve, in some specimens almost straight centrally,

postero-ventral margin sinuous giving a characteristic oblique

58 J.A. ALLEN, H.L. SANDERS AND F. HANNAH

ees Fig. 89 Yoldiella biguttata. Lateral views

of shells from the right and left sides and a

right valve in inner lateral and dorsal view

to show variation in shape and hinge-plate

details. Specimens from Sta. 301 and Sta.

299, Guyana Basin. (Scale = 1.0 mm).

configuration to shell in lateral view; hinge plate moderately

shallow, short, reaching no further than inner limit of adduc-

tor muscles, teeth few, anterior and posterior series either

equal or with one additional tooth in anterior series (5/6 in

largest specimen); ligament amphidetic, very large in relation

to size of shell.

Shell measurements (mm) & ratios are as follows:-

Length Height Width H/L W/L PL/TL

1.64 1.24 0.89 0.75 0.54 0.39

1.62 i172 0.72 0.69 0.44 0.45

1.50 1.07 0.68 0.72 0.45 0.46

1.50 1.08 0.73 0.72 0.49 0.39

3i7/ 1.02 0.70 0.74 0.51 0.47

1.19 0.81 0.48 0.68 0.40 0.39

0.87 0.62 0.33 0.71 0.38 0.40

Prodissoconch length: 198 jm. Maximum recorded shell

length: 1.64 mm.

INTERNAL MORPHOLOGY (Fig. 90). The combined siphon is

thin-walled and with a single lumen. In that the gill axis joins

the ventral edge of the siphon the inhalent component can be

assumed to be largely absent. The siphon is not open ven-

trally. A single fine, elongate mantle tentacle originates on

the left ventral inner limit of the moderately deep siphonal

embayment. An area of secretory cells is present at the base

of the siphon. Ventral to the siphon is a well-developed

feeding aperture. The posterior adductor muscle is round in

cross-section while the anterior is slightly larger and

‘crescent’-shaped. The visceral and cerebral ganglia are well-

developed and joined by a stout commissure. The cerebral a ae

ganglia are slightly the larger. The gills have a relatively small

number of plates (maximum number recorded 9) most of Fig. 90 Yoldiella biguttata. Lateral views from the right and left

which are carried posterior to the foot. Labial palp ridges sides of the internal morphology of a specimen from Sta. 299,

number 14-18, depending on the size of the specimen, and Guyana Basin. (Scale = 1.0 mm). For identification of the parts

are moderately large. The palp proboscides are also moder- sec Hien:

ately large. The foot papillae contain considerable numbers

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

of secretory cells. There is a relatively large single posterior

papilla immeditely posterior to the aperture of the byssal

gland at the heel of the foot. The gland is large and is

surrounded by secretory cells. The hind gut is complex with

twinned loops on each side of the body, with two recurved

sections immediately anterior to the stomach. The main

lateral loops of the hind gut cross from one side of the body to

the other dorsally and immediately posterior to the resilium.

All the specimens examined had well-developed gonads

which makes it difficult to determine the exact course of the

gut, but from sections we are confident that it has a similar

design to that described for Yoldiella subcircularis. One

sectioned female (1.63 mm total length) from Sta. 299 has 18

large ova present (maximum observed dimension 114 .m).

Despite the similarity of the internal morphology to that of

Yoldiella subcircularis the shapes of the shell, hinge and

ligament are totally different in the two species (p. 55). As we

point out elsewhere the various types of hind gut morphology

do not necessarily correlate to a particular characteristic suite

of shell characters. All that can be said with certainty is that

the hindgut of Yoldiella biguttata has configuration so far

found only in the Yoldiellidae and only in species from the

abyss and abyssal rise.

Yoldiella ovata (new species)

TYPE LOCALITY. R.V. Knorr Cruise 25, Sta.300, Guyana

Basin, 29.2.1972, 8°14.2’N, 55°53.5’'W, Anchor Dredge,

2524-2542 m.

TYPE SPECIMEN. Holotype: BM(NH) 1992035. Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

GUYANA BASIN

Knorr 25 300 2524- 208 8°14.2'N 55°53.5'W AD 29.2.72

2542

301 2487- 324 8°12.4'N 55°50.2"W ES 29.2.72

2500

303 2842—- 13 8°28.8’'N 56°04.5'W ES 1 .3.72

2853

Restricted to the abyssal rise of the Guyana Basin. Depth

range: 2487-2853 m.

SHELL DESCRIPTION (Figs. 91 & 92). Shell small, ovate,

moderately inflated, inequilateral, transparent, dorso-

laterally smooth, ventrally, with very fine concentric lines

forming ridges; umbos slightly anterior of midline, moder-

ately inflated, orthogyrate; dorsal margin slightly convex,

antero-dorsal and postero-dorsal margins with similar curva-

Fig. 91 Yoldiella ovata. Lateral views of a shell from the left side

and dorsally and an inner view of a left valve to show detail of the

hinge-plate. Specimens taken from Sta. 300, Guyana Basin.

(Scale = 1.0 mm).

Fig. 92 Yoldiella ovata. Outlines of shells from the right side to

show change in shape with growth of specimens from Sta. 300,

Guyana Basin. (Scale = 1.0 mm).

ture, ventral margin smoothly curved, posterior margin

somewhat more convex than anterior and very slightly

extended, anterior and posterior margins broad, rounded;

hinge plate elongate, moderately wide except below umbo

where narrow, moderately strong, acute taxodont teeth, 7 in

anterior and 8 in posterior series in specimen 2.3 mm;

ligament internal, amphidetic, slightly elongate, barely

extends below hinge plate.

Prodissoconch length: 172 wm. Maximum recorded shell

length: 2.9 mm.

INTERNAL MORPHOLOGY (Fig. 94). The inhalent and exhal-

ent siphons are combined, the inhalent is open along its

ventral margin. The siphonal tentacle is either to the right or

left. There is a feeding aperture and anterior to it a heavily

ciliated region of the inner mantle fold. There is a well-

developed anterior sense organ. The posterior adductor

muscle is small and oval, the anterior adductor, also oval, is

approximately twice the size of the posterior. The labial palps

are moderately large with up to 19 palp ridges and each has a

long thin palp proboscis. The gill which is small, dorsal in

position in preserved specimens, has up to 14 plates. The

visceral and cerebral ganglia are typically ‘club’-shaped, the

visceral being the smaller. The pedal ganglia are moderately

large, elongate and situated high in the foot. The foot is long

and thin with deep papillae fringing the sole. A large byssus

gland is present in the heel.

The stomach and style sac are small and the latter does not

penetrate far into the foot. The hind gut forms double loops

to the left and right of the body, recurring anterior to the

stomach, thus taking a similar course to Yoldiella subcircu-

laris and Yoldiella biguttata. A considerable amount of fine

material was present in the digestive diverticula of the left

side. The kidneys although moderately well-developed do not

W\L e 3 . e ‘

40 . x aus

H\L e io : eo : e

70 : .

PLITL 2 ne

50 . ;

Length(mm)

Fig. 93 Yoldiella ovata. Variation in the ratios of height H/L,

width W/L and postero-umbonal length PL/TL to length against

length of subsample from Sta. 300, Guyana Basin.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 94 Yoldiella ovata. Lateral views from the right and left side

of the internal morphology of a specimen from Sta. 300, Guyana

Basin. (Scale = 1.0 mm). For identification of the parts see Fig.

34.

penetrate anteriorly into the visceral mass to any great

extent. The sexes are separate. One sectioned female (2.7

mm) contained approximately 50 ova with a maximum diam-

eter of 80 pm.

With increasing length, the height/length, width/length and

particularly the posterior umbonal length/total length ratios

gradually increase (Fig. 93).

Yoldiella ovata is closely related to Y. biguttata, but can be

distinguished by its more ovate outline and not being flat-

tened at the postero-ventral shell margin.

Yoldiella insculpta (Jeffreys 1879)

TYPE LOCALITY. West of Ireland, H.M.S. Porcupine, 1869,

Sta. 16, 54°19’N, 11°50’W, 816 fms.

TYPE SPECIMEN. Holotype: not designated. Lectotype: (here

DEEP-SEA PROTOBRANCHIA (BIVALVIA) 61

designated) BM(NH) 85.11.5.459.

Leda insculpta Jeffreys 1879, p. 580, pl. 46, Fig. 5; Dautzen-

berg 1889, p. 80; Dautzenberg & Fischer 1897, p. 204;

Locard 1898, p. 355.

We have examined the material designated as syntypes by

Warén (1980) and housed in the collections of the U.S.

National Museum and the Natural History Museum, London.

MATERIAL.

Cruise Sta DepthNo Lat Long Gear Date

(m)

WEST EUROPEAN BASIN

La Perle DS11 2205 9+2v 47°35.5'N 8°33.7'W DS _ 8. 8.72

(BiogasI) DS13 2165 23+6v 47°33.7'N 8°39.9'W DS _ 10. 8.72

Jean Charcot DS15 2246 5 47°35.2'N 8°40.1'W DS _ 21.10.72

(Polygas) S16 2325" “1 47°36.1'N 8°40.5'W DS 21.10.72

DS18 2138 4 47°31.2'N 8°44.9'W DS 22.10.72

(BiogasII) DS31 2183 4 47°32.5'N 9°04.2'W DS 19. 4.73 ee fis ee

DS32 2138 14 AT-32.2'N. 8°05.3'W DS 19.4:73

(BiogasIII) DS35 2226 18+8v 47°34.4’N 8°40.7'W DS 24. 8.73 Fig. 96 Yoldiella insculpta. Lateral view of shell from the left side

DS36 2147 5 47°32.7'N 8°35.6°W DS 24. 8.73 and an inner view of right valve. Specimens from Sta. 16 and Sta.

Bear 210 Pk Fee Pee 0 NO S28. 73 17 Porcupine Expedition, W. of Portugal. (USNM No. 199773).

DS38 2138 2 47°32.5'N 8°35.8'W__DS_ 25. 8.73 Gees tf a

(Biogas IV) DS61 2250 10+2v 47°34.7'N 8°38.8'W DS_ 25. 2.74

DS62 2175 63 47°32.8'N 8°40.0'W DS _ 26. 2.74

DS63 2126 23+ 47°32.8’N 8°35.0'W DS _ 26. 2.74

10v

DS64 2156 18+ 47°29.2'N 8°30.7'W DS _ 26. 2.74

12v

CP01 2245 8+4v 47°34.6'N 8°38.8'W CP 25. 2.74

(Biogas V) DS65 2360 1 47°36.1'N 8°40.5'W DS _ 15. 6.74

DS71 2194 6+2v 47°34.3'N 8°33.8'W DS_ 20.10.74 i ow

DS87 1913 1 44°05.2'N 4°19.4';W DS 1.11.74

CP08 2177 11+2 44°33.2’N 8°38.5'W CP 20.10.74

CP09 2171 24+4v 47°33.0’N 8°44.0'W CP 20.10.74

Sarsia 65 1922 42 46°15.0'N 4°50.0'W ED 25.7.67

CANARIES BASIN

Discovery 6701 1934 1 27°45.2'N 14°13.0'W ED 16. 3.68

6704 2129 1 27°44.9'N 14°25.0'W ED 17. 3.68

6710 2670 2 27°23.6'N 15°39.6'W ED 19. 3.68

6714 3301 2 27°13.0'N 15°41.0'W ED 20. 3.68

Fig. 95 Yoldiella insculpta. Dorsal and lateral view of shell from

the right side and a lateral view of the hinge-plate of a left valve.

Specimens from Sta. BG IV DS 62, West European Basin.

(Scales = 1.0 mm).

Fig. 97 Yoldiella insculpta. Outlines of shells from the right side to

show variation in shape. Specimens from Sta. BG DS 63, West

European Basin. (Scale = 1.0 mm).

Distributed in the north eastern Atlantic, Bay of Biscay, off

northwest Africa and the Azores at abyssal rise depths.

Depth range: 1354-3301 m.

SHELL DESCRIPTION (Figs. 95-98). Shell ovate, moderately

inflated, smooth with very fine concentric lines near ventral

margin forming slight ridges in larger specimens, occasionally a

few faint radial lines are present in larger specimens; perios-

tracum pale straw-coloured, slightly iridescent; umbos very

slightly anterior of midline, moderately inflated; proximal dor-

sal margin straight or slightly concave on either side of umbo,

antero-dorsal and anterior margin merge in an even curve in

most specimens, distally postero-dorsal margin slopes down to

posterior margin; posterior margin with slight angulation, poste-

rior limit of anterior and posterior margins dorsal to horizontal

mid-plane, ventral margin a smooth curve; hinge plate relatively

narrow, barely extending to outer margins of adductor muscles,

anterior hinge line relatively straight, distally slopes away from

dorsal shell margin, chevron-shaped teeth small, posterior hinge

line slightly curved anteriorly, with same number of teeth in

each series (8/8 in a specimen 2.2 mm and 12/12 in a specimen

3.5 mm); ligament amphidetic, small, rounded, extends below

hinge plate.

Prodissoconch length: c. 190 jm. Maximum recorded shell

length: 3.65 mm.

There is a slight increase in the post-umbonal length as

length increases, otherwise the ratios of height/length and

width/length remain constant.

INTERNAL MORPHOLOGY (Fig. 99). The mantle edge is well-

developed, particularly the inner muscular fold which at its

dorsal edge, contains secretory cells beneath the main rejec-

tion tract. Postero-ventral to the siphons, both the middle

and inner folds are increased in size, convoluted and heavily

ciliated and form a feeding aperture. Exhalent and inhalent

siphons are combined, the latter being open ventrally. A pair

of lateral haemocoelic canals are present the junction

50 e e @ee ee ; $

wit * "stoi.

e oe 0) “coee fy e @ e

e 3 e

H\L C0 ? e

Length(mm)

Fig. 98 Yoldiella insculpta. Variation in the ratios of height H/L,

width W/L and postero-umbonal length PT/TL to length against

length of a sample from Sta. BG IV DS 62, West European

Basin.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 99 Yoldiella insculpta. Lateral views from the right and left

sides of the internal morphology of a specimen from Sta. S 65,

West European Basin. (Scale = 1.0 mm). For identification of

parts see Fig. 34.

between the siphons. The siphonal tentacle is large and found

equally to either the right or left side of the siphonal

embayment. There is a well-developed anterior sense organ.

Adductor muscles are slightly unequal in size, the anterior

being the larger.

Gill plates are relatively small and difficult to count in

preserved specimens (maximum recorded c. 18-20). The

labial palps are well-developed with approximately up to 26

closely spaced ridges on each inner face. The palps extend

between 1/3-1/2 across the body and each bears a long thin

palp proboscis. The mouth is positioned a short distance

posterior to the anterior adductor muscle. The foot is rela-

tively large with a broad sole with a small papilla at the

posterior limit. There is a large byssal gland in the heel (Fig.

100). The arrangement of pedal retractor muscles is similar to

that of other species of Yoldiella. The cerebral ganglia are.

relatively large, the visceral ganglia are small and elongate.

The pedal ganglia lie ventral to the style sac in the proximal

part of the foot and are moderately large. The stomach is

displaced slightly to the right of the body and is of moderate

size with a large style sac. The hind gut configuration is

unique. There are three loops to the right of the body and two

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

loops to the left of the body with a further double loop

passing to the left of the stomach into the foot anterior to the

stomach. The loops do vary slightly in their extent and

curvature. This is similar to the condition in Y. subcircularis,

Y. biguttata and Y. ovata but with an additional loop on the

right. The hind gut has a typhlosole along its entire length.

Fine material similar to that present in the stomach was seen

in the digestive diverticula of a number of specimens. The

kidney is well-developed. Sexes are separate.

The maximum diameter of the ovum as observed in sec-

tions of females from samples taken in February and August

was similar (130 wm). There seems to be a wide variation in

the numbers of ova present. A female collected in August

(2.74 mm) had 255 ova while another collected in February

(3.09 mm) had only 65 ova. Maturing gonads were recorded

for all months sampled.

Yoldiella jeffreysi (Hidalgo 1877)

TYPE LOCALITY. H.M.S. Valorous Sta. 16, Iceland Basin,

west of Rockall Plateau, south Maury Channel, 55°10’N,

25°58'W, 23.8.1875, Dredge, 1785 fm.

TYPE SPECIMEN. Holotype: not designated; Lectotype: U.S.

Natl. Mus., No. 199696 as here designated.

Leda lata Jeffreys 1876, 1876. p. 431 (in part).

Leda jeffreysi Hidalgo 1877, p. 396; Jeffreys 1879, p. 579, pl.

46, Fig. 2; Dall 1881, p. 124; Smith 1885, p. 234; Dautzen-

berg 1889, p. 75; Dautzenberg & Fischer 1897, p.204;

Locard 1898, p. 353.

Portlandia jeffreysi Posselt 1898, p.36.

Yoldiella jeffreysi Verrill & Bush 1898, p. 866, pl. 81, Fig. 5,

pl. 83, Fig. 3.

A holotype of Y. jeffreysi was never designated but the

SF Wh ING

Fig. 100 Yoldiella insculpta. Transverse section through the

‘byssal’ gland. (Scale = 0.1 mm). Abbreviations see p. 12.

following USNM specimens were identified as syntypes by

Warén (1980):-

No. 1999695, Valorous Sta. 9; No. 199694, and No. 199696,

Valorous Sta. 16; No. 199700, Porcupine Sta. 20; No.

199701, Porcupine Sta. 16 & 17; No. 199698 Porcupine Sta.

30.

and in the BM(NH):—

INof /721R18 255" 5Valorous: “Stas.” 955912, 18, 16; No:

85.11.5.592-593, Porcupine Sta. 31; No. 85.11.5 366-367,

Porcupine Sta. 16; No. 85.11.5. 591, Porcupine Sta. 9.

Jeffreys original specimens were taken from the North

Atlantic (Valorous Stations 9, 12, 13 & 16 and from which he

described his species Leda lata (Jeffreys, 1896). Unfortu-

nately the material from these four ‘Valorous’ Stations, which

we have examined, contains two species of Yoldiella which

are, superficially, similar in form (p. ). Furthermore the 1876

description is so general that there is nothing to indicate

which of the two species Jeffreys chose when he described

Leda lata. Thus, we here accept Leda jeffreysi Hidalgo (1877)

as the first unequivocal specific designation and which Jef-

freys (1879) himself accepted two years later.

We have also examined specimens referred to as Yoldiella

Jeffreysi by Verrill & Bush (1898) (USNM, No. 4888) and

these clearly differ from Y. jeffreysis.s. in being stouter, with

a more inflated umbo, a broader hinge plate, with teeth of

different form and fewer in number.

Y. jeffreysi is a very widespread species. It occurs from the

base of the continental slope to the deepest abyssal depth. In

our samples it occurs in the Argentine, Guyana, North

America, West European, Canary, Cape Verde & Angola

Basins. It has also been recorded from the Gulf of Mexico

(2416-2868 m) and from off West Greenland (3200 m) and in

the Mediterranean off Palermo.

Depth range: 2040-4862 m. The depth distribution is

similar throughout the Atlantic.

MATERIAL.

Cruise Sta’ DepthNo Lat Long Gear Date

(m)

NORTH AMERICA BASIN

AtlantisII 64 2886 7 38°46.0'N 70°06.0'W ET 21. 8.64

12 72 2864 6 38°16.0'N 71°47.0'W ET 24. 8.64

Chain 50 76% 82862) 32 °39738:3'N 6757-8 WET 929571665

77 = 3806 109 = 38°00.7’N__ 69°16.0'W_ ET 30. 6.65

78 3828 57 38°00.8'N 69°18.7'W ET 30. 6.65

84 4749 16 36°24.4'N 67°56.0'W ET 4. 7.65

85 3834 413 37°59.2'N 69°26.2'W ET 5S. 7.65

AtlantisII 123 4853 4 37°29.0'N 64°14.0'W ET 22. 8.66

24 1247 AS86295) 1 37526/0'N S9S59'S Ww. ED 2278/66

— 37°25.0'N 63°58.0'W

39°37.0'N 66°47.0'W ET 24. 8.66

— 39°37.S'N 66°44.0'W

126 3806 138

Atlantis1 175 4667— 53 36°36.0'N 68°29.0’'W ES 29.11.67

40 4693 — 68°31.0'W

Chain 106 330 4632 155 50°43.5’'N 17°51.7';W ES 24. 8.72

— 50°43.3'N 17°52.9'W

334 4400 49 40°42.6’N 46°13.8’'W ES 30. 8.72

— 40°44.0'N 46°14.6'W

335 3882- 28 40°25.3'N 46°30.0'W ES 31. 8.72

3919

Knorr 35 340 32164-13 38°14.4'N 70°20.3'W ES 24.11.73

3356

GUYANA BASIN

Knorr 25 287 4980- 5

4934

288 4417- 31

4429

291 3859-155

3868

306 3392— 38

3429

307 3862— 30

3835

ARGENTINE BASIN

AtlantisII 259 3305—- 30

60 3317

WEST EUROPEAN BASIN

Chain 106 316 2173- 85

2209

318 2506 106

321 2290- 94

2968

323 3356- 6

3338

Jean Charcot DS23 4734 1

(Polygas) DS25 2096 2v

(Biogas II) DS31 2813 11

(BiogasIII) DS37 2110 1

DS71 3546 4

(Biogas IV) DS51 2430 27

DS52 2006 1

DS53 4425 1

DS54 4659 1

DS58 2775 10

DS62 2175 1

DS63 2126 1

DS64 2156 §2

CV38 2695 2

(Biogas V) DS68 4550 1

(Biogas VI) DS71 2194 2

DS74 2777 2+2

DS78 4706 1

DS79 4715 2

CP10 2878 1

(Incal) DS01 2091 73

DS02 2081 67

CPO01 2068- 10

2040

CP02 2091 2

CP03 2466 4

CP04 2483—- 2

2513

DS05 2503 123

DS06 1494 243

DS07 2884 267

DS08 2891 32

CPO0S 2884 58

CP06 2888- 39

2893

CP07 2896 17

DS09 2897 274

— 38°17.6'N

13°16.0'N

— 13°15.8'N

11°02.2’N

— 11°03.8'N

10°06.1'N

— 10°06.6'N

9°31.1'N

12°34.4'N

— 12°40.8'N

SPARES)

50°58.7'N

— 50°57.7'N

50°27.3'N

— 50°26.8'N

50°12.3’N

50°08.3'N

46°32.8'N

44°08.2’N

47°32.5'N

47°31.8'N

47°28.3'N

44°11.3'N

44°06.3'N

44°30.4'N

46°31.3'N

47°34.1'N

47°32.8'N

47°29.2'N

47°30.9'N

46°26.7'N

47°34.4'N

47°33.0'N

46°31.1'N

46°30.4'N

47°29.6'N

57°59.7'N

— 57°59.2'N

57°58.8'N

— 57°58.5'N

Se TAN

— 57°56.4'N

57°58.4'N

— S7°S7.7'N

56°33.2'N

— 56°32.5'N

56°33.2'N

— 56°31.5'N

56°28.1'N

— 56°27.6'N

56°26.6'N

— 56°25.9’N

55°00.7'N

— 55°01.0'N

55°02.0'N

— 55°01.9'N

55°00.4'N

— 55°00.9'N

55°02.3'N

— 55°02.6’N

55°03.4'N

— 55°04.4'N

55°07.7'N

— 55°08.1'N

70°22.8'W.

54°52.2'W

54°53.1"W

55°05.5'"W.

55°04.8'W.

55°14.0’'W

55°15.4"W

56°20.6'W.

58°59.3'W.

59°09.2'W

52°45.0'W.

13°01.6’W

13°01.3'W

13°20.9"W

13°19.9'W

13°35.8'W

13°53.7'W

13°50.9'W

10°21.0'W

4°15.7'W

9°04.2'W

8°34.6'W

9°07.2'W

4°15.4'W

4°22.4'W

4°56.3'W

10°29.1'W

9°08.2"W

8°40.0'W

8°35.0'W.

8°30.7'W

8°59.5'W

10°23.9'W

8°33.8'W

9°07.8'W

10°23.8’W

10°27.1'W

9°04.5'W

10°39.8’W

10°41.3"W

10°48.5’W.

10°49.2’W

10°55.0'W

10°42.8'W

10°44.6'W

11°11.3’W

11°12.4'W

11°11.3'W

11°12.4’W

11°11.7'W

11°12.0'W

11°10.5'W

11°10.7'W

12°31.0'W

12°32.0’'W.

12°34.6'W

12°33.4"W

12°29.4'W

12°31.1'W

12°40.3’W.

12°41.7’'W

12°46.4'W.

12°52.6'W.

12°53.2'W

24.

26.

18.

19.

20.

DAE

Zale

Apps

. 3.72

3.71

8.72

26.10.72

1.11.72

IG).

24.

28.

18.

19.

23.

26.

24.

8),

4.73

8.73

2.74

1.74

2.74

6.74

20.10.74

21.10.74

25.10.74

26.10.74

21.10.74

iS),

16.

7.76

16.7.76

16.

17.

18.

19.

20.

7.76

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

CP08 2644 49 50°14.7’N 13°13.5'W CP 27. 7.76

— 50°15.2'N 13°14.8'W

DS10 2719 48 50°12.7'N 13°16.6'W DS 27. 7.76

— 50°13.2'N 13°16.4'W

OS01 2634 794+ 50°14.4’N 13°10.9'W OS 30. 7.76

52v -— 50°15.2'N 13°11.0’'W

WS01 2550- 39+2v 50°19.4'N 13°08.1'W WS 30. 7.76

2539 — 50°19.3'N 13°06.0'W

WS02 2498- 416 = 50°19.3’N_ 12°55.8'W WS 30. 7.76

2505 — 50°20.0'N 12°56.0'W

CP10 4823 1 48°25.5'N 15°10.7'W CP 31. 7.76

— 48°26.3'N 15°09.8'W

DS11 4823 1 48°18.8’N 15°11.5'W DS 1. 8.76

— 48°13.6'N 15°12.0'W

WS03 4829 5+1v 48°19.2'N 15°23.3'W WS 1. 8.76

CP11 4823 2 48°20.4'N 15°14.6'W CP 1. 8.76

— 48°21.1"W 15°13.7'W

OS02 4829 4 48°19.2’N 15°15.7'W OS _ 2. 8.76

DS14 4254—- 1 47°32.8’N 9°35.4".W DS_ 7. 8.76

4248

DS16 4268 1 47°29.8'N 9°33.4,W DS _ 9. 8.76

— 47°30.3'N —9°33.4"W

CANARY BASIN

Discovery 6704 2129 17 27°44.9'N 14°25.0'W ED 17. 3.68

CAPE VERDE BASIN

Discovery 8521 3053—- 90 20°46.9'N 18°43.4,;W WS 25. 6.74

3058 — 20°47.6'N 18°53.5'W

8521 3064- 52 20°47.9'N 18°53.4’W WS 26. 6.74

307 — 20°48.6'N 18°53.4'W

8532 3112— 36 13°47.8’N 18°14.0'W WS _ 5S. 7.74

3119 — 13°48.0'N 18°14.8’W

8532 2952— 20 13°48.2'N 18°08.0'W WS _ 5. 7.74

2958 — 13°47.6'N 18°07.5'W

ANGOLA BASIN

AtlantisII 197 4592- 35 10°29.0'S 9°04.6’E ES 21. 5.68

42 4597

CAPE BASIN

Jean Charcot DS06 4585. 1 =. 33°34.5'N _2°32.9'E_ DS _ 31.12.78

(Walvis)

SHELL DESCRIPTION (Figs. 101-103). Shell ovate, somewhat

inflated, inequilateral, fragile, frequently with broad,

Opaque, concentric banding which is variable in form; umbo

inflated, anterior in position, orientated medially; dorsal shell

margins slope gently from umbo, antero-dorsal, anterior and

antero-ventral margins form a smooth curve, anterior limit of

which lies dorsal to the mid horizontal line, ventral margin

smoothly curved, with posterior limit of shell also dorsal to

mid horizontal line, postero-dorsal margin slightly convex,

slope increases moderately sharply at posterior limit of hinge

plate to join posterior margin to form slight subrostration;

hinge plate, stout, with relatively large chevron-shaped teeth,

posterior series with one or two more teeth than anterior

series (maximum 10 in posterior series), teeth extend as far as

the anterior and posterior margins of anterior and posterior

adductor muscles respectively, hinge plate lies close to shell

margin below umbo; ligament moderately sized, amphidetic,

‘saddle’-shaped in lateral view, extends below hinge plate.

Prodissoconch length: 187-198 »m. Maximum recorded

shell length: 3.7 mm.

The species has a high degree of variation in shape and

within a population may range from the form described above

(the most common) to a more quadrangular outline in which

the deepest part of the ventral margin instead of being

approximately central is posterior to vertical line through the

beaks (Fig. 104). Such specimens may be more inflated.

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Table 2 Yoldiella jeffreysi; ratios of Posterior Length (PL), Height (H), Width (W), to Total Length (TL) and other parameters.

Basin Max.recorded PL/TL

length (mm) (mean)

W. European 3.70 48/60

Incal DSO7 (54)

Canary 3.49 52/58

Sta. 6704 (56)

Cape Verde 2.84 51/56

8521° (54)

N. America 2.54 47/55

Sta. 126 (51)

Guyana 2.96 48/58

Sta. 291 (54)

Argentine 295 44/60

Sta. 259 (53)

Fig. 101 Yoldiella jeffreysi. Lateral view of a shell from the left

side and an inner view of a right valve to show detail of the

hinge-plate. Specimens from Sta. 316, West European Basin.

(Scale = 1.0 mm).

The populations in different basins also differ somewhat in

overall shape (Fig. 105). In the Atlantic, more southerly

populations are somewhat less inflated and large specimens

have an extended posterior margin and thus a more inequilat-

eral shape. Overall, populations in the western Atlantic have

a similar shape to the majority of specimens from the

northern part of the West European Basin and they are

inflated to a similar degree. The more southern populations

are more extended posteriorly. Specimens from the Argen-

tine Basin are slightly more inflated but less so than those

from the northern West European Basin.

It is a general feature of all populations that the width/

length and post-umbonal length/total length increase with

increasing length. In contrast, there is little change in the

height/length ratio (Fig. 105).

The inter- and intra- variability in the shape of populations

of deep sea protobranchs has been noted in many taxa and

most recently for the family Malletiidae (Sanders & Allen

1985). Yoldiellid species are no exception and Y. jeffreysi is

H/TL W/TL ProdissoconchN

(mean) (mean) length (um)

69/75 33/53 187-198 (54)

(72) (45)

68/75 32/48 185-198 (17)

(70) (41)

70/76 38/46 190-200 (52)

(72) (42)

69/77 35/52 182-189 (38)

(73) (40)

69/76 34/43 200-210 (35)

(73) (40)

69/75 36/49 182 (25)

(72) (41)

an extreme example (see Table 2). So much so that we have

made a particular study of this species and we propose to

present our results in more detail in a following publication.

The most closely related (but distinct) species to Y. jeffreysi

is Yoldiella lata. Jeffreys (1876) failed to distinguish between

the two species in his samples from depths where their

distributions overlap (Y. /ata is confined to slope depths (see

p. 32). In general Y. jeffreysi is more inflated than Y. /ata, has

more hinge teeth and the posterior adductor muscle (usually

visible through the shell in live specimens) is smaller and

more elongate.

INTERNAL MORPHOLOGY (Fig. 106-107). The exhalent and

inhalent siphons are combined the latter being open ventrally

(Fig. 106). There is a moderately well-developed feeding

aperture immediately ventral to the inhalent siphon. A large

siphonal tentacle, more frequently on the left side originates

close to the base of the siphon. Antero-ventrally there is a

well-developed mantle sense organ. The adductor muscles

are unequal in size. The anterior is between two and three

times larger than the posterior. The posterior is oval in shape

while anterior is ‘bean’-shaped; the ‘quick’ and ‘catch’ parts

are clearly distinct.

The gills are relatively well-developed with 12-19 alternat-

ing gill plates, the number depending on the size of the

animal. The most posterior plate lies close to the junction

between the inhalent and exhalent siphons and to which the

gill axes join. The labial palps are relatively small with long

and slender palp proboscides. In their contracted state they

extend across one quarter to one third of the body. The palps

have been 11-14 palp ridges, again the number depending on

the size of the animal. The foot is large and in some

specimens it is preserved in a very long, anteriorly extended

fashion. It has a deep papillate sole. A large byssal gland is

present and in many specimens in the region of its aperture at

the posterior margin of the foot there is a considerable

amount of mucous material present.

The species has a very large stomach, the dorsal wall of

which lies close to the hinge plate, the stomach lies off centre

slightly to the left. A large style sac penetrates deep into the

foot. The gastric shield extends close to the opening of the

oesophagus, the latter slightly to the right on the antero-

dorsal wall. Right and left digestive diverticula are anterior

within the body and material similar to that found in the

stomach was observed in sections of both right and left

diverticula. The hind gut forms a clockwise loop to the right

()

Shell length (mm)

iN)

1 5 9

No. of teeth

Fig. 103 Yoldiella jeffreysi. The relationship of the number of

hinge-teeth to shell length of a subsample from Sta. 316, West

European Basin. The left and right limits of each bar indicate the

number of anterior and posterior hinge-teeth respectively.

anterior of the body, thereafter describing an ‘S’-shaped bend

before continuing as an anticlockwise loop which partially

overlies the first. Thereafter it runs parallel to and immedi-

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 102 Yoldiella jeffreysi. a, lateral view of a

right and left valve of a specimen from the

Jeffreys collection labelled Leda lata (USNM

No. 199695, Valorous Expedition, Sta. 9). b, a

dorsal and lateral view from the right side of a

specimen from Sta. INCAL DS 06, West

European Basin. (Scale = 1.0 mm).

ately below the dorsal margin to the anus (see Fig. 107). A

typhlosole is present along its entire length. The configura-

tion of the hind gut on the right side of the body, despite

being somewhat variable is characteristic of this species (Fig.

108). It can be very simply visualized as a doubled length of

rope making one and a half turns (Fig. 107). In this species,

more than any other we have examined, there is a consider-

able variation in the course of the hind gut which can easily be

resolved by reference to the rope analogy (Fig. 107). It would

appear that this manner of accommodation of a long hind gut

is particularly susceptible to distortion during development,

possibly because of displacement due to the large size of the

stomach and the anterior arrangement of the digestive diver-

ticula or possibly because the loop tends to impede its own

development in this particular configuration (Fig. 105).

The nervous system is well-developed with moderately

large ‘club’-shaped cerebral ganglia, slightly smaller elongate

visceral ganglia and large, oval, pedal ganglia. Dorsal to the

latter are large, round, statocysts, filled with refractile gran-

ules. The visceral ganglia lie some distance anterior to the

posterior adductor.

The populations from the different basins have similar

internal morphologies.

Sexes are separate and the gonads overlie other internal

organs. Gonad development was followed in two Incal

samples (DS07, DS09; West European) and one Discovery

sample (8521 No. 1, Cape Verde). In West European speci-

mens the number of ova ranged from 160 (108 um maximum

diameter) in a female 2.1 mm long to 350 (144 wm max.

diameter) in a female 3.1 mm long. The females from the

Cape Verde Basin (2.2, 2.5 & 2.7 mm total length) contained

fewer eggs 41-103 but these had a slightly larger size range

130-156 pm.

In July/August samples, maturing gonads had become

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Fig. 104 Yoldiella jeffreysi. A comparison of selected specimens

from a number of deep-sea Basins showing the range in shell

shape. The shell outlines of each specimen are drawn in dorsal

and right lateral view. a & b, Sta. 197, Angola Basin; c, Sta. 288,

Guyana Basin; d, Sta. 334, North America Basin; e & f, Sta. 259,

Argentine Basin; g, Sta. 316, West European Basin; h, Sta. 85,

North America Basin. (Scale = 1.0 mm).

obvious (Fig. 109) and by October the gonads had largely

filled the body.

Yoldiella enata (new species)

TYPE LOCALITY. R.V. Knorr, Sta. 301, Guyana Basin,

29.1.1972, 8°12.4’N, 55°50.2’W, Epibenthic Dredge,

2487-2500 m.

TYPE SPECIMEN. Holotype: BM(NH) 1992033. Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

GUYANA BASIN

Knorr 25 301 2487—- 175 8912.4'N 55°50.2'W ES 29. 1.72

2500

303 2842—- 23 8°28.8'N 56°04.5'W ES Ie Se 2

2853

W\L Sree

oe @ Suse °

40 ost j

ieee ees

H\L e ote Z e ge? a

W\L j ~

40 —<—e Mies a

HIL F tae aah aos 2

Length(mm)

Fig. 105 Yoldiella jeffreysi. Variation in ratios of height H/L, width

W/L and postero-umbonal length PL/TL to length against length

of a, samples from Sta. 126, North America Basin (large closed

circles) and Sta. 259, Argentine Basin (points); and of b, samples

from Sta. INCAL DS 07, West European Basin (points) and Sta.

6704, Canary Basin (large closed circles).

NORTH AMERICA BASIN

Atlantis II 118 1135- 20 32°99.4’'N 64°34.9"'W ES

1153 — 32°19.0'N 64°34.8"W

18. 8.66

Several specimens of this species are included in a mixture of

species contained with U.S. Natl. Mus. No. 108197, labelled

Yoldiella pygmaea Munst. None of these correspond to Leda

Fig. 106 Yoldiella jeffreysi. Siphons as seen from the ventral side

of a preserved specimen form Sta. 85, North America Basin.

(Scale = 0.1 mm).

Fig. 107 Yoldiella jeffreysi. Lateral views from the right and left

sides of the internal morphology of a specimen from Sta. 85,

North America Basin. (Scale = 1.0 mm). For identification of

parts see Fig. 34.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 108 Yoldiella jeffreysi. Diagrammatic views of the course of

the hind gut as seen from the right side to show variations in the

configuration.

pygmaea Munst. as exemplified by U.S. Natl. Mus. No.

197285.

Distributed in the western Atlantic from southern limit of

the North America Basin to Guyana, from mid to lower slope

depths. Depth range: 1135-2853 m.

SHELL DESCRIPTION (Figs. 110 & 111). Shell ovate, not

particularly inflated, moderately elongate, slightly inequilat-

eral, faint concentric striae particularly close to ventral mar-

gin; umbo moderately large; postero-dorsal and antero-

dorsal margins slightly convex and slope gently from umbo,

anterior margin rounded, anterior limit dorsal to mid hori-

zontal plane, dorsal and ventral margins without angulation,

antero-ventral margin smooth curve, postero-ventral margin

very slightly sinuous posterior margin not angulated, broadly

blunt, posterior limit in mid horizontal plane; hinge moder-

ately broad distally, narrows centrally, chevron-shaped teeth

robust, close set with ventral arm twice length of dorsal,

anterior and posterior plates with up to 7 teeth; ligament

amphidetic, moderately large, extends ventral to hinge plate.

Prodissoconch length: — 287 ~m. Maximum recorded shell

length: 3.65 mm.

This species is similar to Yoldiella ella, however it is less

round in outline, shallower dorso-ventrally and less inflated.

The ligament is also similar to that of Y. ella as is the hinge

plate, however, the latter in Y. ella is more broad and bears

one or two more teeth than that in Yoldiella enata.

INTERNAL MORPHOLOGY (Fig. 112). This is similar to that of

Yoldiella ella so much so that it is extremely difficult to

distinguish between the two species. Such distinction as there

is is a matter of slight difference in proportion. Thus, the

anterior adductor muscle is slightly larger, the diameter of the

hind gut is slight less and the exhalent siphon is somewhat

larger than in Y. ella. Sections of the tightly coiled hindgut

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

ahOoDND =

pL roti [es

ze l ly. 3 .

aes

ESS SSS

NESSaeSEs

GEnSsg

2 SER BEE RAT

ES Ins lh

MR x mm re Ms Shy alll

Z| th, Popp ome 1) RSX ‘ RS JX

VRS ea 4 I

‘ila

Vy)

NESE

SSS

SISSS SAN

ans

SSE

;

All

Zo 2X2

DP &

Length (mm)

Fig. 109 Yoldiella jeffreysi. Length frequency histogram superimposed by a gonadial index. 1, immature, no gonadial development seen in

the intact specimen; 2, first sign of gonadial development at ventral edge of visceral mass; 3, gonad surrounds the periphery of the visceral

mass; 4, gonad covers half the visceral mass; 5, visceral mass wholly covered by gonad. Top, females; bottom, males.

Fig. 110 Yoldiella enata. Lateral view of a shell from the right side

and detail of the hinge-plate of a left valve. Specimen from Sta.

301, Guyana Basin. (Scale = 1.0 mm).

show the same number of coils. In a specimen 3.1 mm the

palps, which are moderately small, have 14 internal ridges.

The palp proboscides are large and broad. The kidney is large

and extends anteriorly lateral to the stomach. The largest

specimens are mature and in the case of one sectioned

specimen a few eggs were present in the mantle cavity. This is

not taken as evidence of brooding.

It is clear that Yoldiella enata and Yoldiella ella are very

closely related, however, we have no difficulty in distinguis-

ing them from their shell features. It should also be noted that

the depth distribution of the two species is very different,

Yoldiella enata is found on the lower slope while Yoldiella ella

is truly abyssal.

Yoldiella ella (new species)

TYPE LOCALITY. R.V. Chain Sta. 334, North America Basin,

30.9.1972, 40°42.6’N, 46°13.8’W — 40°44.0’N, 46°14.6’W,

Epibenthic Trawl, 4400 m.

TYPE SPECIMEN. Holotype: BM(NH) 1992034. Paratypes in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta Depth No _ Lat Long Gear Date

(m)

NORTH AMERICA BASIN

AtlantisII 72 2864 1 38°16.0'N 71°47.0'W ET 24. 8.64

Chain 50 TO) 286205) 1 99 39238-3°N G7 57-28) W JET, 29,6165

78 3828 38°08.0'N 69°18.7'W ET 30. 6.65

85 938347) Il 9 37259:2°N | 69926:2.W ET ¥5297.65

AtlantisIT 126 3806 4 39°37.0'N 66°47.0’'W ET 24. 8.66

24 — 39°37.5'N 66°44.0'W

Chain 106 334 4400 44 40°42.6’'N 46°13.8’'W ES 30. 8.72

— 40°44.0'N 46°14.6'W

Fig. 111

Yoldiella enata. Outlines of shells from the right side to

show variation in shape with growth of specimens from Sta. 301,

Guyana Basin. (Scale = 1.0 mm).

Fig. 112 Yoldiella enata. Lateral view from the right side of the

internal morphology of a specimen from Sta. 301, Guyana Basin.

(Scale = 1.0 mm). For identification of the parts see Fig. 34.

335 3882— 26 40°25.3'N

3919

Knorr 35 340 3264- 16 38°14.4'N

3356 — 38°17.6'N

SIERRA LEONE BASIN

AtlantisII 148 3814 1 10°37.0'N

31 3818

149 3861 25 10°30.0'N

155 3730- 7 00°03.0'S

3783

156 3459 4 00°46.0'S

— 00°46.5'S

ANGOLA BASIN

AtlantisII 197 3865- 2 10°29.0’'S

42 4595

198 4559- 4 10°24.0’S

4566

199 3764—- 2 9°47.0'S

46°30.0'W.

70°20.3'W

70°22.8'W

18°14.0'W

18°18.0'W

27°48.0'W.

29°28.0'W.

29°24 .0'W

9°04.0'E

9°09.0'E

10°29.0'E

31.

8.72

24.11.73

21.

22.

5.68

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

3779

WEST EUROPEAN BASIN

Chain 106 323 3356 9

3338

326 3859 12

328 4426 9

4435

330 4632 137

Jean Charcot

(Polygas) DS20 4226 25

DS21 4190 8

DS22 4144 14

DS23 4734 2

(Biogas III) DS41 3548 1

DS42 4104 1

(BiogasTV) DS55 4125 80

DS56 4050 §= 3

DS60 3742 6

Cyros

(Biogas V) DS66 3480 21

DS67 4150 4

DS68 4550 3

Jean Charcot

(Biogas VI) DS75 3150 4

DS76 4228 243

DS77 4240 55

DS78 4706 3

DS79 4715 9

DS80 4720 3

CP13 4134 2

Jean Charcot 0S02 4829 8

(Incal) OSOS 4248- 9

4296

0S66 4316- 43

4307

0SO7 4249 63

OSO8 4327 42

WS03 4829 7+2v

WS07 4281-— 30

4274

WS08 4287-

4301

WS09 4277

WS10 4354

DS11 4823

DS14 4248- 20

4254

DS15 4211

DS16 4268

CP11 4823

— 9°49.0'S

50°08.0'N

50°04.9'N

= 50°05.3’N

50°04.7'N

50°43.5'N

— c50°43.4’N

47°33.0'N

47°31.5'N

47°34.1'N

46°32.8'N

47°28.3'N

47°32.1'N

47°34.9'N

47°32.7'N

47°26.8'N

47°28.2'N

47°31.0'N

46°26.7'N

47°28.1'N

47°34.8'N

47°31.8'N

46°31.2'N

46°30.4'N

46°29.5'N

47°34.4'N

48°19.2'N

47°31.3'N

— 47°32.2'N

46°27.3'N

— 47°27.9'W

47°31.8'N

47°29 .8'N

— 47°29.5'N

48°19.2'N

— 48°19.1'N

47°30.6'N

— 47°31.2'N

47°30.5'N

— 47°29.3'N

47°28.8'N

— 47°27.9'N

47°27.3'N

— 47°28.3'N

48°19.2'N

47°32.6'N

— 47°32.9'N

47°33.6'N

47°29 .8'N

— 47°20.2'N

48°20.4'N

— 48°21.1'N

10°33.0’E

13°53.7'W

13°50.9'W

14°23.8’W

14°24.8'W

15°44.8'W

17°51.7'W

17°52.9'W

9°36.7'W

9°40.7'W

9°38.4'W

10°21.0'W

9°07.2'W

9°35.6'W

9°40.9'W

9°28.2'W

9°07.2'W

9°00.0'W

9°35.0'W

10°23.9'W

9°07.8'W

9°33.3'W

9°34.6'W

10°23.8’W

10°27.1'W

10°29.5’W

9°38.0'W

15°15.7'W

9°34.6'W

9°34.7'W

9°36.2'W

9°36.0'W

9°34.3'W

9°39.2'W

9°38.8'W

15°23.3’W

15°22.5’W

9°37.1'W

9°35.7'W

9°33.7'W

9°34.1'W

9°34.0'W

9°39.9'W

15°23.3'W

15°22.5'W

9°35.7'N

9°35.1'W

9°39.1'W

9°38.5'W

9°33.4'W

15°14.6'W

15°13.7'W

GP.

ZN; 8.72

22. 8.72

235 8.42

24. 8.72

24.10.72

25.10.72

26.10.72

26. 8.73

27. 8.73

22. 2.74

23. 2.74

24. 2.74

16. 6.74

17. 6.74

19. 6.74

22.10.74

23.10.74

24.10.74

25.10.74

26.10.74

27.10.74

23.10.74

2. 8.76

7. 8.76

95 816

10. 8.76

11. 8.76

1. 8.76

7. 8.76

9. 8.76

10. 8.76

14. 8.76

1. 8.76

71. 810

8. 8.76

9. 8.76

1. 8.76

Widely distributed throughout much of the Atlantic in North

America, West European, Sierra Leone and Angola Basins

at abyssal depths. With only two exceptions, all records are

greater than 3200 m. Depth range: 2862-4829 m.

SHELL DESCRIPTION (Figs. 113-116). Shell ovate, moderately

inflated, inequilateral, shell with very fine concentric lines,

ventral lines usually more conspicuous, few fine radial lines

from umbo to ventral edge, periostracum light straw colour;

umbo large, rounded, orthogyrate, anterior to midline, great-

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Fig. 113 Yoldiella ella. Lateral view of a shell from the right side

and a left valve to show detail of the hinge-plate. Specimens from

Sta. INCAL 0S 06. (Scale = 1.0 mm).

est shell height posterior to umbo; dorsal margin slightly

convex, antero-dorsal anterior and ventral margins in a

smooth continuous curve, postero-ventral margin rounded

posteriorly, posterior margin in small specimens may have

very slight, blunt, angulation, posterior limit slightly dorsal to

horizontal midline, postero-dorsal margin curves gently from

umbo to distal edge to hinge plate then slopes more acutely to

posterior margin; hinge plate, long, characteristically angular

below umbo, moderately broad proximally, narrow ventral to

umbo, anterior and posterior ventral margins of hinge plate

more or less straight, teeth strong, well-developed, equal

number in anterior and posterior plates, up to 9 in specimen

4.2 mm, ligament amphidetic, moderate in size, rectangular

or slightly ‘goblet’-shaped, short, wide, posterior external

extension and long slender anterior external extension of

fused periostracum.

Prodissoconch length: 166 ~m. Maximum recorded shell

length: 4.2 mm.

There is little change in the width/length or height/length

ratios with increasing size, however, posterior umbonal

length increases slightly and the posterior margin becomes

more smoothly curved.

INTERNAL MORPHOLOGY (Fig. 117). The anterior sense

organ is well-developed. Posterior mantle fusion is minimal,

limited to a fine bridge of tissue between the opposing inner

mantle lobes forming a short exhalent siphon. The gill axis is

attached laterally on either side of the bridge tissue. Ventral

to it the inhalent siphon is reduced to a pair of unfused

thickened pads of tissue. The feeding aperture is poorly

developed with a few gland cells present. Immediately ante-

rior to the feeding aperture, the inner mantle fold is enlarged

—

Fig. 114 Yoldiella ella. Outlines of shells from the right side to

show variation in shape with growth of specimens from Sta. BG

VI DS 76, West European Basin. (Scale = 1.0 mm).

slightly and more obviously ciliated and may possibly indicate

a temporary point of adhesion in the living specimen. The

siphonal tentacle is usually to the left ventral side of the

shallow mantle embayment. The adductor muscles are rela-

tively small, approximately equal in size and more or less oval

in shape. There are up to 16 gill plates and the gills are

attached far posterior on the body wall. The gill axis is

well-supplied with muscle fibres. The labial palps, like the

gills, are relatively small with up to 14 ridges on their inner

faces with the result that in preserved specimens, there is a

marked separation of gill and palp which is unlikely to be true

in life. The palp proboscides are relatively long and broad.

The foot is of moderate size with a relatively wide neck and

an elongate, deeply divided sole. There is a large byssal gland

in the heel with a concentration of cilia around its opening.

The heel has a terminal papilla. The cerebral and visceral

ganglia are relatively small and ‘club’-shaped in lateral view.

The pedal ganglia is larger and slightly elongate.

The oesophagus has a wide opening into a large stomach.

The combined style sac and mid gut extend into the dorsal

half of the foot. The digestive duct from the right diverticu-

lum skirts dorsal to the hind gut loops to open into the

anterior wall of the stomach. On the left and close to the

oesophageal aperture is a relatively wide digestive duct from

Length(mm)

Fig. 115 Yoldiella ella. Variation in ratios of height H/L. width

W/L and postero-umbonal length PL/TL to length against length

of a sample from Sta. BG VI DS 76, West European Basin.

Numbers

1 2 3 4

Length(mm)

Fig. 116 Yoldiella ella. Length frequency histogram of a sample

from Sta. BG VI DS 76, West European Basin.

the left anterior diverticulum. This latter opens mid-laterally

into the stomach. A second duct from the posterior digestive

diverticulum of the left side opens into the left wall of the

stomach below the gastric tooth. The course of the hind gut is

first anterior and then antero-ventral to the pedal ganglia

before turning back on itself to pass dorsally posterior to

the stomach. Thereafter it forms a series of complicated

coils to the right side of the body the design of which can be

derived from a doubled strand coiled clockwise as seen

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

from the right side (Fig. 117). The hind gut then passes to

the mid postero-dorsal margin and thence dorsal to the

posterior adductor muscle to the anus. There is a relatively

shallow typhlosole along the length of the hind gut. Faecal

rods were seen cradled by the gill axes between anus and

the siphon.

The kidney and heart are well-developed. The sexes are

separate. Animals smaller than 2.15 mm total length were all

immature with no obvious gonad present. The number of ova

varies from 16 in an individual 2.57 mm (maximum diameter

of ova 87 mm) to 90 in an individual 3.2 mm long (maximum

diameter of ova 132 ym). In samples collected in February,

June, August and September in specimens of 2.15 mm and

above, all have maturing ova.

Y. ella has all the characteristics of a shallow burrowing or

semi-submerged species i.e. a rounded, broad form, with

short siphons in a shallow siphonal embayment. Many speci-

mens bear hydroids attached to antero-ventral and ventral

margins.

Two intact specimens of a species of Yoldiella in which the

external shell features appear to be close to Y. ella (or

possibly Y. enata) were taken at Sta. 199 from the Angola

Basin at a depth of 3771 metres (Fig. 118). We have hesitated

to examine the internal anatomy of these. Unfortunately

because of the opaqueness of the shell all that can be seen of

the hind gut is part of one or possibly two coils to the right of

the body, close to the anterior adductor. These specimens

could either prove to be a new species or showing variation of

shell form.

Yoldiella fabula (new species)

TYPE LOCALITY. R.V. Chain Cruise 50, Sta, 85, North

America Basin, 5.7.1965, 37°59.2'N, 69°26.2’W, Epibenthic

Trawl, 3834 m.

TYPE SPECIMEN. Holotype: BM (NH) 1992037. Paratypes: in

collection held by J.A. Allen.

Leda sericea Jeffreys 1879, p. 579 (in part). Two specimens

were found in the Jeffreys collection (U.S. Natl. Mus. No.

199590 (Fig. 119a) and No. 199589 (Fig. 119b)). Although

these are labelled L. sericea and must have been so

identified by Jeffreys they clearly differ from that species.

A specimen stored with and labelled Yoldiella expansa

(U.S. Natl. Mus. No. 697343 (Fig. 119c)) is also this

species. All these specimens were collected off West Ire-

land in 2500-2670 metres.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

NORTH AMERICA BASIN

Atlantis II 62 2496 39°26.0’N 70°33.0'W ET 21. 8.64

12 64 2886 38°46.0’N 70°06.0'W ET 21. 8.64

67°58.0'W ET 23. 8.64

71°47.0'W ET 24. 8.64

69°16.0'W ET 30. 6.65

70 ©4680

72 2864

Chain 50 77 ~—-3806

36°23.0'N

78 3828 6

38°16.0'N

1 38°07.0'N

38°08.0'N 69°18.7°;W ET 30. 6.65

84 4749 36°24.0'N 67°56.0'W ET 4. 7.65

85-3834” cl3" 37°S92'N 69°26.2°W ET 52 7265

AtlantisII 92 4694 36°59.2’N 69°26.2".W ET 5. 7.65

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Fig. 117 Yoldiella ella. Details of the internal morphology. a & b, whole mounts from the right and left sides respectively; c, ventral view of

contracted siphon; d, ventral view of the sole of the foot and hindgut; e, course of the hindgut as seen from the right side. (Scales = 1.0

mm).

AtlantisII] 125 4825 1

Knorr 35 340 3264 1

3356

ARGENTINE BASIN

AtlantisII 242 4382- 8

60 4402

243 3815- 10

3822

247 5208- 16

5223

256 3906- 3

3917

WEST EUROPEAN BASIN

Chainl06 323 33536— 2

3338

330 4632 1

Jean Charcot DS21 4190 1

(Polygas) DS23 4734 2

37°24.0'N

— 37°16.0'N

38°14.4'N

— 38°17.6'N

38°16.9'S

37°36.9'S

43°33.0'S

37°40.9'S

50°08.0'N

— 50°08.3'N

50°43.5'N

— 50°43.4'N

47°31.5'N

46°32.8'N

65°54.0'W

65°50.0'W

70°20.3'W

70°22.8'W

51°S6.1"W

52°23.6’W

48°58.1'W

52°10.3’W

13°53.7'W

13°50.9'W

IGE SMRIEN SY

17°52.9'W

9°40.7'W

10°21.0'W

Ed,

23.

8.66

24.11.73

13;

14.

N7/.

24.

21.

24.

3.71

SH/I|

Suri

3.74.

8.72

24.10.72

26.10.72

(Biogas IT)

(Biogas III)

(Biogas IV)

(Biogas V)

(Biogas VI)

(Incal)

DS28 4413

CV13 4252

DS30 4160

DS41 3548

DSS0 2124

DSS55 4125

DS56 4050

DSS7 2906

DS66 3480

DS67 4150

DS76 4228

DS84 4466

WS07 4281

WS08 4287

QS06 4316

QS07 4249

Bee < BNP WP

44°23.8'N

47°31.8'N

47°38.3'N

47°18.3'N

44°08.9'N

47°34.9'N

47°32.7'N

47°31.7'N

47°28.2'N

47°32.0'N

47°34.8'N

44°25.4'N

47°30.6'N

— 37°31.2'N

47°30.5'N

— 47°29.3'N

46°27.3'N

— 47°27.9'N

47°31.3'N

— 47°31.3'N

4°47.5'W

9°34.2'W

9°33.9"W

9°07.2'W

4°15.9'W

9°40.9'W

9°28.2'W

9°06.2"W

9°

9°35.0'W

9°33.3'W

4°52.8'W

9°37.1'W

9°35.7'W

9°33.7'W

9°34.1'W

9°36.2'W

9°36.0'W

9°34.3'W

Pema lG/72

25.10.72

18. 4.73

26. 8.73

i 9273)

22. 2.74

23. 2.74

24. 2.74

16. 6.74

17. 6.74

23.10.74

29.10.74

TAS 16

9. 8.76

LO Sr6)

DS05 2503. 1 56°28.1’N 11°11.7'W DS _ 18. 7.76

— 56°27.6'N 11°12.0'W

DS09 2897 7 55°07.0’N 12°52.6'W DS _ 20. 7.76

— 55°08.1'N — 12°53.2"W

DS14 4254- 1 47°32.6'N 9°35.7'W DS _ 8. 8.76

4548 — 47°32.9'N —-9°35.5'W.

DS16 4268 2 47°29.8'N 9°33.4';W DS_ 9. 8.76

— 47°30.3'N —-9°33.4"W.

GUINEA BASIN

DS20 2514 2 2°32.0'S 8°18.1'W DS

SIERRA LEONE BASIN

AtlantisII 149 3861 1 10°30.0’N 18°18.0'W ES 7. 2.67

ANGOLA BASIN

AtlantisII 195 3707 7 14°49.0'N 9°56.0'W ES 19. 5.68

42 — 14°40.0'N —-9°54.0"W

196 4612— 2 10°29.0'N 9°03.0'W ES 21. 5.68

4630 — 10°29.5'W =: 9°04.0"W.

197 3865- 5 10°29.0’'N 9°04.0'W ES 21. 5.68

4595 — 10°29.0'N 9°04.0'N

198 4559- 10 10°24.0'N 9°09.0'W ES 21. 5.68

4566 — 9°47.0'N 10°29.0'W

199 3764- 2 9°49.0’N 10°33.0'W ES 22. 5.68

3779 — 9°41.0'N 10°55.0'W

GUYANA BASIN

Knorr 25 291 3859- 1 10°06.1’N 55°14.0'W ES 26. 2.72

3868

303. 2842— 2 8°28.8’'N 56°04.0'W ES 1. 3.72

2853

Y. fabula is wide-spread at abyssal depths throughout the

Atlantic in small but persistent numbers in most of the

Atlantic Basins. Low population density and low sampling

density probably explains the lack of records in the Guyana &

Canaries Basins. Depth range: 2503-5223 m.

SHELL DESCRIPTION (Figs. 119-121). Shell small, moderately

swollen, ‘bean’-shaped, inequilateral, post umbonal length

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 118 Yoldiella sp. Lateral views of two shells taken from Sta.

119, Angola Basin. (Scale = 1.0 mm).

40-46% of total length, sculpture regular with conspicuous

ridges, periostracum straw coloured, often discoloured and

brown at valve margins; umbo relatively large, posterior in

position and inflated, directed posteriorly; proximal dorsal

margins slightly convex either side of umbo, proximally

evenly curved to rounded anterior and posterior margins,

ventral margin long, smooth curve; hinge plate moderately

Fig. 119 Yoldiella fabula.

Lateral views of two shells

from the right and left sides

respectively and a left valve

to show details of the

hinge-plate. a, Jeffreys

collection USNM No. 199590

labelled Leda sericea Jeffr.

St. 21, 1476 fm. N.W.

Ireland, Porc. Ex. 1870; b,

USNM No. 199589 labelled

Leda sericea Jeff. St. 19a,

1366 fm, W. of Ireland, Porc.

Ex. 1869; c, USNM No.

697343 labelled Yoldiella

expansa Jeffreys 49°37'N,

13°34'W. S.W. of Ireland.

(Scale = 1.0 mm).

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

strong, extends almost to outer limit of both adductor

muscles, anterior hinge plate with 1-2 more teeth than

posterior, total number of teeth up to 17 depending on size,

distal teeth small and difficult to identify; ligament internal,

slightly opisthodetic, ‘goblet’-shaped with posterior extension

ventral to hinge plate.

Prodissoconch length: 229 wm. Maximum recorded shell

length: 3.1 mm.

The shell outline in this species is somewhat variable (Figs.

120 & 121). It is the only yoldiellid species indeed species in

our collections, with this highly characteristic ‘bean’-shape.

For a time we misidentified Yoldiella fabula as Y. dissimilis

Verrill & Bush 1898. On closer examination we note that Y.

dissimilis unlike Y. fabula is ‘nearly equilateral, that the

anterior hinge is oblique that the number of hinge teeth is

greater and that an oblong prominent tooth-like process at

the proximal end of the posterior hinge series is not present.

Y. fabula, as all other yoldiellids, has only very small external

anterior and posterior componants visible which are derived

from secondary fused periostracum.

The range in length of the specimens in the collection

varies from 1.72 mm to 3.08 mm. The following are the

overall proportions:- H/L ratio 0.63-0.72; W/L ratio

0.41-0.50; and PL/TL ratio 0.40-0.46. Although these ratios

vary the overall range is related to growth and to some

variation in the populations.

INTERNAL MORPHOLOGY (Figs. 122 & 123). Ventral to the

anterior adductor muscle the middle lobe of the mantle is

modified to form a well-developed anterior sense organ. The

combined siphon has a single lumen which is open ventrally.

The gill axes join laterally indicating an inhalent as well as an

exhalent component. A small, single, tentacle is present close

to the postero-ventral margin of siphonal embayment.

Numerous groups of glandular epithelial mantle cells are

found peripheral to the inner siphonal aperture and the

feeding aperture and anterior to the latter.The adductor

muscles are large and approximately equal in size. The

posterior adductor is oval in cross section while the anterior is

‘crescent-shaped with ‘catch’ and ‘quick’ portions clearly

marked.

The gills are parallel to the dorsal posterior shell margin

with up to 17 well-developed plates. The distal gill filaments

lie close to the siphon. Moderately large labial palps extend

approximately halfway across the body and have up to 20

ridges on their inner surface. The foot is well-developed with

a narrow neck and a deeply divided sole. At the heel there is

a conspicuous median papilla directly posterior to the open-

ing of the byssal gland. The byssal gland is well-developed.

The pedal musculature is similar to Y. /ata. Both cerebral and

visceral ganglia are cylindrical and moderately well-

developed with a stout connecting commissure. The pedal

ganglia are circular and not particularly large.

The oesophagus, stomach, and style sac are basically

similar to those of Y. /ata. A long duct from the right

digestive diverticula passes dorsally over the hind gut to enter

the stomach close to the oesophageal aperture. The duct from

one left diverticulum opens slightly more posteriorly on left

ventral wall, while the duct from the second left diverticulum

opens ventral to the gastric tooth on the left side. The hind

gut has a typhlosole and forms a single loop to the right side

of the body.

Initially the gonads develop ventral to the digestive diver-

ticula and the hind gut loop, but gradully they spread

posteriorly and dorsally to the stomach. A female 2.5 mm

long, from a July sample had approximately 74 large ova

(maximum diameter 180 1m) while a second female of similar

size (2.3 mm) had 62 ova (maximum diameter 160 pm). The

gonadial aperture is close to that of the kidney, and anterior

to the posterior pedal retractor muscle. The large kidney

extends from the postero-dorsal margin to the foot and

anteriorly over the viscera to a point just anterior to the

lateral pedal retractor muscle. A large pericardial cavity is

present.

Yoldiella veletta (new species)

TYPE LOCALITY. R.V. Jean Charcot, Biogas VI, Sta. DS87,

Bay of Biscay, 31.10.1974, 44°05.2'N, 4°15.7'W, Epibenthic

Trawl, 1913 m.

TYPE SPECIMEN. Holotype: Museum National d’Histoire

Naturelle, Paris.

MATERIAL.

Cruise Sta. Depth No Lat Long Gear Date

(m)

CANARIES BASIN

Discovery 6701 1934 1 27°45.2'N 14°13.0'W ES 16. 3.68

CAPE VERDE BASIN

145 2185 1 10°36.0'N 17°49.0'W ES 6. 2.67

WEST EUROPEAN BASIN

Jean Charcot

Biogas VI DS87 1913 1 44°05.2'N 4°15.77;W ES 31.10.74

Distributed on the lower slope in the eastern Atlantic from

the Bay of Biscay to the Cape Verde Islands. Depth range:

1913-2105 m.

SHELL DESCRIPTION (Fig. 124). Shell moderately swollen,

Fig. 120 Yoldiella fabula. Lateral view of a shell from the right

side and detail of the hinge-plate of a left valve. Specimens from

Sta. BG VI DS 84, West European Basin. (Scale = 1.0 mm).

W\L ee:

40 ‘en eieiaees

H\L e e e ‘ e

& t. Us .

Length (mm)

Fig. 121 Yoldiella fabula. Variation in ratios of height H/L. width

W/L and postero-umbonal length PL/TL to length against length

of specimens taken by the Biogas Expeditions as listed in the

table of material.

ovate, inequilateral, sculpture, fine concentric lines and

growth rings, no lunule, no escutcheon; umbo large, poste-

rior to midline, directed to posterior; antero-dorsal margin

merges with anterior margin in smooth curve, limit of ante-

rior margin close to midline, ventral margin long, shallow

curve, limit of posterior margin ventral to midline, proximal

postero-dorsal margin slopes more steeply than antero-dorsal

margin and results in narrowing of post umbonal shell in

lateral view; hinge plate moderately strong, except ventral to

umbo where it is very narrow, hinge teeth strong, somewhat

elongate, 1 or 2 more teeth in anterior series; ligament

amphidetic, largely ventral to hinge margin; no chondro-

phore.

Prodissoconch length: 165 wm. Maximum recorded shell

length: 4.56 mm.

INTERNAL MORPHOLOGY (Fig. 125). The combined siphon

has a single lumen which is open ventrally, as in Y. fabula.

The siphonal embayment is deep, a fine tentacle is present on

the right side. The adductor muscles are particularly large but

approximately equal in size, the anterior being fractionally

the larger. The anterior sense organ is not particularly

well-developed. The gill is elongate and attenuated with up to

27 plates. The palps are large each with up to 13 internal

ridges. The foot is also large and with papillate margins

anteriorly directed. The stomach is moderately large and the

hind gut forms a single loop to the right side of the body. The

hind gut has a wide diameter and a single typhlosole is

present along its entire length.

This species has clear affinities with species of Portlandia.

Nevertheless, it is a fragile shell without any trace of lunule or

escutcheon. On the basis of only three specimens, the shell

morphology seems most similar to Y. fabula.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 122 Yoldiella fabula. Lateral view from the right side of the

internal morphology of a specimen from Sta. 85, North America

Basin. (Scale = 1.0 mm). For identification of parts see Fig. 34.

Fig. 123 Yoldiella fabula. External views of intact stomach an style

sac in a, left; b, right and c, antero-frontal views. Dissected from

a specimen from Sta. 85, North America Basin. (Scale = 1.0

mm).

Genus Portlandia Morch 1857

TyPE. By selection (Soot-Ryen, 1984: Opinion 769 ICZN)

Nucula artica J.E. Grey, 1824.

Shell moderately small, slightly inflated, moderately frag-

ile, oblong, posteriorly angular, more or less truncate, sub-

rostrate, not gaping, escutcheon present, usually defined by

weak or occasionally moderate carina, lunule may be present;

usually glossy, smooth, postero-ventral margin may be sinu-

ous, proximal postero-dorsal margin almost straight or

slightly concave; umbo prominent, anterior, chondrophore

variously developed; ligament amphidetic, largely internal

with small part external, hind gut single loop to right of body.

Portlandia lenticula (Moller 1842)

TYPE LOCALITY. Greenland.

TYPE SPECIMEN. Lectotype BM(NH) 1843.7.3.31, right-hand

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Fig. 124 Yoldiella veletta. Lateral views of two shells from the right

side, detail of the hinge-plate of a right valve and a dorsal view of

a shell. Specimens form a, Sta. 145, Cape Verde Basin; b & c,

Sta. BG VI DS 87, West European Basin; d, Sta. 6701, Canaries

Basin. (Scales = 1.0 mm).

Fig. 125 Yoldiella veletta. Lateral view from the right side of the

internal morphology of a specimen from Sta. 145, Cape Verde

Basin. (Scale = 1.0 mm). For identification of parts see Fig. 34.

specimen of 5 mounted specimens; Paralectotypes BM(NH)

1843.7.3.27-30 4 mounted specimens.

Nucula lenticula Moller 1842, 17.

Portlandia lenticula Sars 1878, 39, tab. 4, Fig. 10a,b; Thiele

1928, 617; Ockelmann 1958, Fig. 13, pl. 1, Fig. 12.

Yoldia (Yoldiella) lenticula Richards 1962, pl. 1, Figs, 23, 24.

Fig. 126 Portlandia lenticula. Lateral view of a shell from the right

side from Sta. S44, West European Basin. An interval view of a

right valve with an enlarged detail of the hinge-plate and a dorsal

view of a shell. Specimens from North East Atlantic (det. K.

Ockelmann). (Scales = 1.0 mm).

Fig. 127 Portlandia lenticula. Lateral view from the right side of

the internal morphology of a specimen from Sta. S44, West

European Basin. (Scale = 1.0 mm) for identification of the parts

see Fig. 34.

Yoldiella lenticula Dautzenberg & Fischer, 1912, 406; Scar-

lato 1981, 209. Fig. 113.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

WEST EUROPEAN BASIN

Sarsia 44 1739 4

Thalassa 2438 1400 3

43°40.8'N

48°33.7'N

3739-22W ED 16.57.67

10°15.0'W PBS 26.10.73

Jean Charcot DS37 2110 1 47°31.8’N 8°34.6'W DS 24. 8.73

(Biogas III)

(Biogas IV) CPO01 2245 2 47°34.6'N 8°38.8’'W CP 25. 2.74

CANARY BASIN

Discovery 6704 2129 1 27°44.9'N 14°25.0'W ED 17.3.68

This is predominantly a northern Atlantic species occurring

mostly from 10-200 metres (Ockelmann, 1958). Neverthe-

less, there are sufficient past records to confirm the present

identifications that at its southern limits it is present at lower

slope depths. Perhaps indicative of a temperature/depth

relationship.

SHELL DESCRIPTION (Fig. 126). Shell moderately stout,

ovate, slightly inequilateral, fine concentric lines, with elon-

gate lunule and escutcheon, shell very wide dorsally and

medially (such that when it rests on a valve the dorsal part is

centred so that both umbos are characteristically visible in the

lateral view); umbo very large, raised, internally directed,

orthogyrate, immediately anterior to midline; antero-dorsal

margin joins anterior and antero-ventral margins in a smooth

curve, postero-dorsal margin also joins posterior and postero-

ventral margin in smooth curve but is more attenuate than

anterior margin; hinge plate moderately stout, not quite

reaching level with the outer margins of adductor muscles,

hinge plate narrows almost to margin below umbo, anterior

and posterior hinge teeth equal in number or with one

additional on the posterior plate; ligament amphidetic large,

globular, extending far ventral to the hinge plate, slight

secondary anterior and posterior external extension of fused

periostracum. (See Ockelmann 1958, for typical shell dimen-

sions).

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

INTERNAL MORPHOLOGY (Fig. 127). The combined siphons

are short within a relatively shallow siphonal embayment.

There is a slender sensory tentacle on the right side. The

anterior sense organ and the feeding aperture are not particu-

larly well-developed. The adductor muscles are very large,

more or less oval in shape the anterior being the larger in size.

The gills are slender with approximately 13 plates in a small

specimen 14 mm in length. The palps are large with 13 ridges.

The foot is small and in the one whole mount contracted to

the level of the ventral edge of the palps. There is a small

byssal gland. The stomach is large and the hind gut stout, the

latter describes a single loop on the right side of the body.

Portlandia fora (new species)

TYPE LOCALITY. R.V. Sarsia, Sta. 56, Bay of Biscay,

19.7.1967, 43°43.0'N, 3°47.8’W, Epibenthic Trawl, 641 m.

TYPE SPECIMEN. Holotype: BM (NH) 1992041. Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta’ Depth No Lat Long Gear Date

(m)

WEST EUROPEAN BASIN

Sarsia 56s 641 1S 43°43.0'N 3°47.8'W ED _ 19.7.67

Only taken from the Bay of Biscay at one Station on the

upper slope. Depth 641 m.

SHELL DESCRIPTION (Fig. 128). Shell relatively stout,

Fig. 128 Portlandia fora. Lateral

view of a shell from the left side and

a dorsal view of the same shell, detail-

of the hinge-plate of a left valve and

lateral views of two small specimens

to show variation in shape with

growth. Specimens from Sta. S 56,

West European Basin. (Scales = 1.0

mm).

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

inflated, ovate, inequilateral; umbos inflated, orthogyrate,

anterior to midline; proximal dorsal margin slightly convex,

antero-dorsal margin convex, slightly angulate at limit of

hinge plate, then relatively straight section to dorsal limit of

anterior margin, antero-ventral margin and ventral margin

smoothly curved, posterior margin drawn out into broad

rounded medial tip, postero-dorsal margin slightly convex

sloping gradually towards tip, slight dip in outline at limit of

hinge plate, posterior margin slightly rostrate; no marked

rostral ridge but a small lunule and escutcheon present close

to umbos; hinge plate moderately broad, long strong teeth,

12 in posterior and 10 in anterior series in largest individual,

ligament internal, amphidetic, moderately large, ‘goblet’-

shaped, short anterior and posterior external extensions of

fused periostracal.

Maximum observed shell length: 3.86 mm.

INTERNAL MORPHOLOGY (Fig. 129). Well-developed com-

bined inhalent and exhalent siphons are present, the inhalent

siphon is somewhat the shorter than exhalent. The siphonal

tentacle is usually on the left side. The anterior sense organ is

well-developed. The adductor muscles are relatively small.

The anterior adductor is ‘cresent’-shaped and approximately

twice the size of the oval posterior adductor.

The gills have up to 14 alternating filaments. The labial

palps are small, extending over approximately 1/4 distance of

body and have up to 9 inner palp ridges. The palp probos-

cides are long and thin. The visceral ganglia are relatively

slender, the cerebral ganglia are larger and more oval in

shape and the pedal ganglia are large and round. The foot is

moderate in size with a large byssal gland. There is a

relatively large stomach with the style sac ventral and slightly

posterior to it. The hind gut penetrates deep into the foot

ventral and anterior to the pedal ganglia before turning

dorsally to umbonal region where it passes to the right side of

the body and forms a single loop. The hind gut has a

typhlosole along its length.

This species is similar in shell shape and internal morphol-

ogy to Portlandia minuta but differs from the latter in that P.

fora has a less angulate shell margin, slightly larger internal

Fig. 129 Portlandia fora. Lateral view from the right side of the

internal morphology of a specimen from Sta. S 56, West

European Basin. (Scale = 1.0 mm). For identification of parts see

Fig. 34.

ligament, a more obvious external ligament, is less inflated

and has a greater number of hinge teeth, the hinge plate is

narrower, and the post-umbonal length shorter. Anatomi-

cally there are relatively few differences, the gill plates and

palp ridges are marginally fewer in specimens of a similar

size.

Portlandia minuta (new species)

TYPE LOCATION. R.V. Atlantis, II Cruise 42, Sta. 203,

Angola Basin, 23.5.1968, 8°48’S, 12°52’E, Epibenthic Trawl,

527-542 m.

TYPE SPECIMEN. Holotype BM (NH) 1992040. Paratypes: in

collection held by J.A. Allen.

MATERIAL.

Cruise Sta Depth No Lat Long Gear Date

(m)

CAPE BASIN

AtlantisI] 188 619-622 33 23°00.0'S 12°58.0’E ES 16.5.68

ANGOLA BASIN

Atlantis 42 203 527-5S44352 8°48.0’S 12°52.0’E ES 23.5.68

Occurs off S.W. Africa at upper slope depths in Angola &

Cape Basins. Depth range: 527-622 m.

SHELL DESCRIPTION (Figs. 130 & 131). Shell small, inflated,

subovate, posteriorly narrow, robust, fine but somewhat

irregular concentric lines; slightly iridescent, pale yellow

periostracum; umbos inflated, anterior to midline, internally

directed; lunule and escutcheon barely visible; slightly ros-

trate, slight indication of rostral ridge in some specimens;

antero-dorsal margin convex, slopes rapidly and evenly to

anterior margin, postero-dorsal margin slightly convex,

slopes gradually to posterior margin, slight angle at limit of

posterior hinge plate, ventral margin smoothly curved, cen-

trally deep, posterior margin drawn out but moderately

rounded, in mid horizontal plane; hinge plate strong, fairly

narrow on either side of ligament, broadens out distally,

distal teeth prominent, 3-4 small proximal teeth, in total 9 in

anterior series and 11 in posterior series of largest specimen;

ligament amphidetic, rectangular in shape, small external

secondary extensions of fused periostracum on either side of

umbo.

Prodissoconch length: 166 ~m. Maximum recorded shell

length: 2.28 mm.

INTERNAL MORPHOLOGY (Fig. 132). There is a combined

siphon with a single lumen, thus there is no separation

between inhalent and exhalent lumena, however, the gill axes

join mid-laterally. Gland cells are present at the junction of

axis and siphon. There is a well-developed elongate anterior

sense organ. The adductor muscles are unequal in size. The

smaller posterior muscle is oval in shape, the anterior is

almost twice the size and ‘cresent’-shaped. The gills are

well-developed with up to 14 relatively large plates, the most

posterior of the inner plates are clearly interlocked even in

the preserved specimens. The labial palps are relatively small

with up to 8 palp ridges, the most posterior of these being

much broader than the rest.

The foot is large but the pedal musculature is not as

well-developed as in some Yoldiella species. There is a large

60 °

80 Aseria

H\L ° e &, *~ QO

Length (mm)

Fig. 131 Portlandia fora. Variation in ratios of height H/L, width

W/L and postero-umbonal length PT/TL to length against length

of a subsample taken from Sta. 203, Cape Basin.

byssal gland in the heel with a relatively large blood space

surrounding it. The nervous system is well-developed with

large ‘club’-shaped visceral and cerebral ganglia and large,

round, pedal ganglia with associated large statocysts dorsal to

them. The stomach and style sac are large. From the style sac

the hind gut penetrates the foot for a short distance before

turning dorsally to parallel the posterior edge of the body.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 130 Portlandia

minuta. Lateral views of

shells from the left and

right sides, detail of the

hinge-plate of a left valve

and the dorsal view of a

shell. Specimens from Sta.

203, Cape Basin. (Scale =

1.0 mm).

Thereafter it makes a single loop to the right side of the body.

A small amount of food material was observed in parts of the

left digestive diverticulum. The kidneys are small. Gonads

are present in specimens larger than 1.6 mm. The testes occur

dorsally, ventrally and internally to the digestive diverticula

with posterior dorsal and lateral extensions.

In the course of growth, the valves become more inflated

and more rostrate but there is little change in the height/

length or posterior umbonal length/ total length ratios (Fig.

131). Hydroids were present on one individual and these

covered the dorsal and posterior shell margins.

Fig. 132 Portlandia fora. Lateral view from the right side of the

internal morphology of a specimen from Sta. 203, Cape Basin.

(Scale = 1.0 mm). For identification of parts see Fig. 34.

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Fig. 133. Portlandia abyssorum. Lateral views of three shells from

the right side to show variation in shape. Dorsal view of a shell

and detail of the hinge-plate of a left valve. Specimens taken from

a, Sta. 24, Galathea Expedition, Sierra Leone Basin (Type

specimen); b, c & d, Sta. 8528', Cape Verde Basin; e, Sta. 8521°,

Cape Verde Basin. (Scales = 1.0 mm).

Portlandia abyssorum (Knudsen 1970)

TYPE LOCALITY. R.V. Galathea, Sta. 24, E., Atlantic off W.

Africa, 1950, 3°54'N, 8°22'W, Trawl, 3196 m.

TYPE SPECIMEN. Holotype: Zoological Museum, University

of Copenhagen.

Yoldiella abyssorum Knudsen 1970, 47, Fig. 29, pl. 1, Fig. 17.

MATERIAL.

DepthNo Lat | Long Gear Date

(m)

Cruise Sta

CAPE VERDE BASIN

Discovery 8521° 3070-6+2v 20°47.9'N 18°53.4'W WS 26. 6.74

3064

8528' 3155— 72+2v 17°38.7'N 18°35.8'W WS 2. 7.74

3150 — 17°38.3'N 18°34.9'W

AtlantisII 148 311141 10°370°N) “18*1420'W ES: 9 °7-92167

31 3828

149 3861 3 10°30.0'N 18°18.0'W ES _ 7. 2.67

ANGOLA BASIN

AtlantisIT 195 3797 45 14°40.0'S _ 9°54.0'E ES 19. 5.68

42 196 4612- 1 10°29/0'S, ) 9°54/01B) ES) 21675268

4630 — 10°29.0'S 9°04.0’E

CAPE BASIN

Jean Charcot DS05 4560 1 33°205'S) 2349'E DS —30:12.78

(Walvis) €P1393550» 1 SPAS aS 13-15 1O0E ei CP ele 79)

Occurs at abyssal depths off the west coast of Africa, Cape

Verde, Angola & Cape Basins. Depth range: 3064-4630 mm.

SHELL DESCRIPTION (Figs. 133 & 134). An accurate descrip-

tion is given by Knudsen (1970). Populations of this species

vary somewhat in the shape of the shell outline from that of

the type specimen to specimens with a more straight or

slightly concave postero-dorsal margin and a more convex

postero-ventral margin with intermediates between these two

extremes.

INTERNAL MORPHOLOGY (Fig. 135). In contrast to the

description of Knudsen (1970) there is an inhalent as well as

an exhalent siphon. The short ventral inhalent siphon is not

particularly obvious being much shorter than the exhalent,

however, sections show a twin siphon, the inhalent being

open ventrally. A siphonal tentacle originates on the left of

the siphon and there is a fairly well-developed feeding

aperture below. The adductor muscles are large, the anterior

being approximately twice the size of the posterior. The gills

are well-developed with up to 24 gill filaments. The labial

palps are large with a large number of internal ridges (up to

30), the number depending on the size of the individual. The

foot is large and extends anterior and ventral to the anterior

adductor muscle. It also has a large byssal gland. The cerebral

and visceral ganglia are elongate with a moderately thick

commissure. The pedal ganglia are large, elongate with large

associated statocyts. The hind gut forms a single loop on the

right side of the body and has a typhlosole along its length.

Prodissoconch length: 187-198 4m. Maximum recorded

shell length: 4.76 mm.

This species at first sight might be confused with Yoldiella

biscayensis, however there are a number of differences.

These include: — the presence of a lunule and escutcheon; the

umbo is raised only slightly above the dorsal margin; the

posterior and postero-dorsal margin is faintly rostrate; the

prodissoconch is much narrower and is shorter in length; the

palps have many more ridges.

ay Ue e

A a

a a ° °

a a a: a Fn aie, te oe o*~egee,

a a4 a A eee feos core 4

7 a, AB ee Os i

60-PL\TL ; :

\ e

a e eae

e O eo e

a FOS A ORS ORO Sate o.

a a Aa eens Mh 7° @ee

Soa

80-H\L ,

a a a pS ee a a, eal Gos

2 4

Length (mm)

Fig. 134 Portlandia abyssorum. Variation in ratios of height H/L

width W/L and postero-umbonal length PL/TL to length against

length of specimens from Sta. 195, Angola Basin (closed

triangles) and Sta. 8528', Cape Verde Basin (closed circles).

Fig. 135 Portlandia abyssorum. Lateral view from the right side of

the internal morphology of a specimen from Sta. 8528', Cape

Verde Basin. (Scale = 1.0 mm). For identification of the parts see

Fig. 34.

DISCUSSION

Of all the protobranch bivalves of the Atlantic, the yoldiellids

are by far the most difficult nuculanid subgroup in which to

discern evolutionary pathways. Despite the large number of

species we believe that these are closely related within a

subfamily. With possibly one exception, of 28 species of

Yolidella described here, there is a fine gradation in morpho-

logical features that both combines them within a single genus

and distinguishes them as a separate group. It must be

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

emphasized that as in all deep-sea protobranch species, the

shell proportion changes with increasing size. In general the

post-umbonal length increases at a rate greater than the other

dimensions. In some cases this also applies to the height of

the shell. As a result the small shells of a species may be

mistaken as being of a different species. This also creates

difficulties in making comparisons between species.

To the experienced eye, species and subspecies can be

separated and defined. Of particular diagnostic importance is

the form and course taken by the hind gut. Although there

may be some variation within a species, the course and

diameter of the gut alone is usually diagnostic. Nevertheless,

it is often difficult to define and only becomes clear after close

comparison of a range of species. We can distinguish eight

broad configurations of the hindgut of which the simplest, a

single loop to the right of the viscera occurs in 17 of 32 species

and subspecies of Yoldiella (Table 3) (Allen, 1992). The most

complex configuration occurs in only one species (see below).

The species of Portlandia form a compact group in which

the shells are relatively robust, elongate, with the posterior

margin approximately central to the horizontal midline. The

hind gut has a single loop to the right and has a large

diameter. The adductor muscles are large and oval and more

or less equal in size. The hinge plates are long and stout,

continuous with the amphidetic internal ligament. The lunule

and escutcheon are usually well-defined. Three of the four

species are from upper to mid-slope depths and one P.

abyssorum, is from abyssal depths. The latter, apart from

having larger palps, smaller adductor muscles and more

dorsal anterior and posterior limits to the shell outline than

the other species described, its morphology is basically the

same.

One rare species of Yoldiella, Y. veletta, has many of the

characteristics of Portlandia described above. However, it is a

fragile shell without lunule or escutcheon. Furthermore, the

hinge plates form in a narrow bridge below the umbo with the

amphidetic ligament ventral to it. With only three specimens

at hand we defer categorical judgement, but hypothesize that

the primitive form of Yoldiella must have had similar charac-

teristics.

On the premise that the simplest form of hind gut is likely

to reflect the primitive condition we derive an evolutionary

pattern that originates in species with this character but

among others, for it is unwise to base evolutionary conclu-

sions on one character alone. In passing, it should be said that

it is a sad fact that for many malacologists, it is the shells

rather than the viscera that are all-important.

It seems reasonable to assume that deep-water species in

the Atlantic originated either from shallow water, possibly

tethyan and arctic seas, or by migration at depth from the

Southern Ocean. For reasons that we will describe elsewhere

(Allen and Sanders in m/s), we think it unlikely that the

major colonization of the deep Atlantic was from high

southern latitudes. Yet there are only a limited number of

yoldiellids present in shelf sediments, but all of these species

have a relatively short hindgut with a simple single loop to the

right side of the viscera. This character is also found in other

shallow-water nuculanids and in shallow-water neilonellids

and tindariids, however, species of Yoldiella differ from these

latter three groups in not having heavy, concentrically orna-

mented shells. When concentric ornamentation is present in a

yoldiellid it is always of a fine, delicate nature, and more

often than not confined to the periphery of the shell.

We identify two species from shallow water in the North

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

and West Atlantic, Y. frigida and Y. robusta that have

characters which we believe a ‘stem’ group might possess.

These include, in addition to the single hind gut loop, a

symmetrical ovate shell outine, relatively short fragile sepa-

rate hinge plates and a moderately large central amphidetic

ligament (Fig. 148). In addition, they have large siphons with

combined lumena which are ventrally unfused, moderately

large, oval, subequal, adductor muscles, a few large fringing

papillae to the foot, a relatively elongate gill with a moderate

number of plates and broad palp ridges which are relatively

few in number.

From this basic form, we derive a number of evolutionary

pathways. The most simple derivation appears to be that

shells become somewhat higher in proportion to length and

the antero-dorsal and postero-dorsal margins become more

horizontal such that the anterior and posterior limits of the

shell are dorsal to the horizontal midline (Figs. 136-147).

(For details of the comparative overlay technique, see Fig.

136). In other respects, a characters are similar to those given

above. These latter species include Y. inconspicua, Y. extensa

and Y. argentinensis, again from the North and West Atlantic

but further downslope than Y. frigida and Y. robusta. In

addition, Y. curta, a common and widespread species from

the base of the continental slope would also appear to belong

here, however, unlike the species mentioned so far, the

hindgut of Y. curta passes anterior to the mouth to form a

single loop on the left side of the body. This disposition of the

hind gut is a simple derivation from the primitive condition

and can be explained simply in terms of elongation and

accommodation of the hindgut. In all other respects Y. curta

is similar to the species of the Y. frigida group.

In juxtaposition to this possible stem group is a group of

species centred upon Y. lucida (shelf/upper slope), Y. obesa

(mid/lower slope) and Y. similiris (upper/mid slope).

Although having similar ovate shape to Y. frigida and Y.

robusta, these species have much longer but still separated

hinge plates, smaller adductor muscles of which the posterior

is significantly smaller than the elongate anterior muscle. The

hind gut loops are somewhat longer and more broadly looped

and the lumena have a wider diameter. Most other characters

are in common with the ‘stem group’. These include an

internal amphedetic ligament ventral to the hinge plate which

is somewhat smaller than that of the stem group, a relatively

elongate gill, small palps with broad ridges which are few in

number and papillae of the foot which are relatively large.

The differences between Y. lucida, Y. obesa and Y. similiris

and the species of the ‘stem group’ relate to the strength of

the hinge plate. As the length and robustness of the hinge

increases there is less requirement for large adductors and a

large ligament to ensure the integrity of the two valves. In

addition, as the maximum depth limit of the species

increases, the hind gut tends to enlarge either in length or

diameter or both.

As in the case of the ‘stem group’, we believe evolution

from the ‘/ucida’ group also involves an increase in the height

of the shell and the antero- and postero-dorsal shell margins

becoming more horizontal such that the posterior limit of the

shell margin becomes characteristically sharply rounded. The

posterior adductor muscle is reduced in size, the hind gut

penetrates deep into the foot and the palps are small with

very few ridges. The siphonal lumena are separate. Species

with these characterstics include Y. bilanta, Y. hanna and Y.

capensis, all of which are restricted to slope depths.

Y. artipica is intermediate in its characters to the two above

groups, however the hind gut is more sinuous in its course to

the right. This represents the initial stage in a trend that leads

to the coiling of the hind gut on the right side of the body.

Note the Y. artipica has a deeper distribution than those

species described above and is found on the abyssal rise.

Similarly, Y. sinuosa, Y. blanda and Y. biscayensis which

have similar characteristics to the ‘bilanta’ group, all have

sinuous hind guts. There are other internal differences shown

by these three species. Thus, while the adductor muscles are

dissimilar in size, the posterior muscle is not greatly reduced

in size, the palp ridges, although wide, are more numerous

and thus the palp is large and the siphon is particularly large

with combined lumena. As in the case of Y. artipica these are

species from the abyssal rise.

The logical sequence to the trend is seen in Y. /ata in which

the hind gut has a larger diameter, has lengthened such that

the ‘reverse-S’ course has progressed to a double-loop. Also

to be noted are that the adductors are moderately large and

are equal in size, and the hinge plates, although elongate, are

narrow and much less robust. Similarly the gill is relatively

small and the palp has numerous narrow ridges.

As a continuation of this trend, a specialized group of

species comprising Y. ella, Y. enata and Y. jeffreysi is arrived

at. A sequence of events can be envisaged. Starting from the

condition in Y. /ucida the hind gut lengthens, remains to the

right of the body and becomes increasingly coiled. (Up to

four times). The shell becomes characteristically rounded,

high with large umbos. The hinge plates become very strong

and the ligament small and rounded. The adductor muscles

are small, and may be subequal in size. The generating

outline curve of the shell is rotated somewhat to the right so

that the umbo is distinctly anterior and the maximum ventral

limit is posterior to the vertical midline. We can envisage a

sequence of increasing hind gut complexity from Y. lucida

through Y. blanda, Y. lata, Y. jeffreysi to Y. enata, however,

we have some reservations as to whether Y. ella is the

terminal species of this line. While Y. e/a has the most coiled

hind gut of all the yoldiellids in our collections, the more

evenly rounded shape, the extremely small subequal adduc-

tor muscles and the massive hinge plates might indicate a

separate derivation or at least a marked terminal divergence

in the series. These species have a depth distribution from the

abyssal rise to the greatest abyssal depth. There is little doubt

in our opinion that the differences in morphology exhibited in

both the latter group are related to the requirements of life at

abyssal depths.

We also derive an even more complex but distinct group

comprising Y. americana, Y. subcircularis, Y. biguttata and Y.

ovata from the Y. lucida stock. These four species also have

characteristically rounded, high shells which have large

umbos. The evolutionary sequence probably included an

intermediate stage with a form similar to that of Y. perplexa

in which shell characters are similar but in which there is a

relatively short single hind gut loop to the right, robust

subequal adductor muscles, small palps and gills, large pedal

papillae and long hinge plates. Y. americana differs relatively

little from this, except that the hind gut is considerably

lengthened and which takes a course to the left and right of

the stomach and the palp is a deep semicircular shape with a

large number of ridges (see p. 54). A similar morphology to

that of Y. americana is found in Y. subcircularis except that

the hindgut loops are doubled on either side of the body.

Similarly, Y. biguttata and Y. ovata also have two hind gut

loops to the right and the left and in Y. insculpta, the hind gut

84 J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 136 Yoldiella frigida (f), Y. robusta (r), & (separately) Y.

curta(c).

Fig. 137 Yoldiella argentinensis (a), Y. extensa (e) & (separately)

Yoldiella inconspicua inconspicua (1), Y. i. profundorum (p) & Y.

i. africana (a).

Fig. 138 Yoldiella lucida (\), Y. similirus (s) & Y. obesa incala (0).

Fig. 139 Yoldiella bilanta (b), Y. hanna (h) & Y. capensis (c).

Figs 136-147 Outline comparisons of species by overlay technique. Each outline is centred with reference to the junction of the centre of the

mid-length axis with the centre of the mid-height axis. Outlines are drawn to a similar length. Each shell outline comprises the margin in

right lateral view, hindgut loop and anterior and posterior adductor muscles. Anterior, posterior ventral and dorsal limits are indicated

parallel to the relevant shell axis as too is the apex of the umbo. Each limit is identified by the first letters of the species name. The figures

are in the order of the discussion on the evolution of form. (See text pp. 82-86).

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

Fig. 140 Yoldiella artipica (a), Y. similis (s) & (separately) Y.

lata(p).

Fig. 141 Yoldiella sinuosa (s), Y. blanda (bl) & Y. biscayensis (bi).

Fig. 143 Yoldiella ella (el).

Fig. 144 Yoldiella americana (a), Y. subcircularis (s) & Y. perplexa

(p).

86 J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Fig. 147 Portlandia abyssorum (a), P. minuta (m), P. fora (f),

(separately) Yoldiella velleta (v) & Portlandia lenticula (1).

Fig. 145 Yoldiella ovata (0), Y. biguttata (b) & (separately) Y.

insculpta (i).

Fig. 146 Yoldiella fabula (f).

DEEP-SEA PROTOBRANCHIA (BIVALVIA)

robust shells with lunule & escutcheon

long broad continuous hinge

large adductors

P.minuta

P fora

P. lenticula

P abyssorum :

<< fragile shells without lunule & escutcheon

==> eer —2 separate hinge plates

moderately large subequal adductors

Y. frigida

Y.robusta

Y.veletta

hind gut thru’ :

to left 2

Y.curta —_______| ¥.frigida _ |--------- fill be. > Y.fabula

short hinges

Y.inconspicua

Y.extensa

Y.argentinea

ous : Y.lucida

on INnges rk

small cineyltal aildictors A: Y.obesa_

(/ 2 Y.similiris

Fe) * ‘

‘s’ shaped hind guts Y.artipica =

Y.bilanta : ‘

Y.hanna : !

Y.capensis :

: single

Y. sinuosa : hind gut loop

Y. blanda N

Y.biscayensis | Y.perplexa |

. v . s

Y.pseudolata Y.similis Y.americana

ovate Y.subcircularis

Y.enata coils loops Y. biguttata multiple

Y.jeffreysi Y. ovata hind gut loops

& coils

Y.ella Y.insculpta

increasing

shell height

&hind gut length

Fig. 148 Diagram to show resemblances in shell form of the deep-sea species of the genus Yoldiella found in the Atlantic, arranged in

increasing length and complexity of the hindgut and each group of species arranged in increasing depth sequence.

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

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DEEP-SEA PROTOBRANCHIA (BIVALVIA)

is further extended to three loops to the right and two to the

left with one loop on each side short and anterior to the

stomach. The latter is a configuration unique among proto-

branchs. In these relatively large rounded species the liga-

ment tends to be relatively large and the hinge plates robust

and elongate. Most of these species extend from the abyssal

rise across the abyssal plain.

Comparison of this latter group with Y. similis is of

interest. While Y. similis species has a double hind gut loop

its anatomy is similar to Y. artipica. In particular it has small

palps with a few broad ridges.

One species of Yoldiella remains to be mentioned. Yoldi-

ella fabula differs markedly in its shell characters from all

other species of Yoldiella (and Portlandia) yet in its internal

morphology it is close to the basic stem group of the genus.

Thus, while it is elongate with the umbo set far posterior to

the mid-vertical line, it has relatively short separate hinge

plates with a small amphidetic ligament. Very large subequal

adductors are present and the hind gut is a simple, single loop

to the right. Although its shell outline is unique, these

characters fit best with the yoldiellids and we are presently

persuaded to keep it within this subfamily.

In the foregoing discussion, stress has been placed on

changes in the shape of the shell and the disposition of the

gut. It is clear that for the most part species that occur at great

depths have longer guts than those in shallow water and that

this increased length has been accommodated within a small

body space. This in turn relates to the digestive requirement

to deal with sparse complex organics in deep-sea sediments.

Indeed, in general the body space of deep-sea bivalves as a

percentage of shell volume is significantly smaller than that of

shallow-water congeners. Similarly, in regard to shell shape,

species in shallower depths appear to be of an elongate-ovate

shape, whereas those from the deep have higher shells which

are either more rounded or have the greatest length measure-

ment dorsal to the mid-horizontal plane. This we believe is

related to the softness of the abyssal sediments and the ease

of movement within them.

There are other evolutionary trends that may or may not be

depth related. For instance, the size of the adductors clearly

relates inversely to the strength and length of the hinge plates

and the size of the ligament. In contrast, the size of the palps

appears to increase with increasing depth range, while gills

tend to reduce in size. We believe this is for a different reason

from that of the change in shape of gut and shell, and relates

in part to a difference of energy demand at high pressures and

in part to the lack of importance of the protobranch gill in the

feeding process. Because of this latter there is a reduction in

the size of the gill, however, the loss in ciliated tissue is

compensated by an increase in palp area which is required in

order to maintain ciliary flow within the mantle cavity. At the

same time it provides ciliary activity where is is most needed

in the processing of fine abyssal sediments.

As might be expected the siphons also show modifications.

Reduction in the gill area results in lower inhalent siphonal

flow rates. In contrast, larger palp surfaces result in higher

inflow via the feeding aperture. The processing of large

quantities of fine sediment must produce increased numbers

of faecal pellets. The predicted result from these changes is

realized in the increased importance and size of the feeding

aperture, the reduction and in some cases elimination of the

inhalent siphon or the loss of division between exhalent and

inhalent siphonal lumena such that the combined siphon is

largely used for the passage of faecal material to the outside.

Finally, we speculate that not only that the small size of the

body in comparison with the shell volume in the deep-water

species is related to reduced food resources (as in reduced

numbers of ova) but it is also related to the reduction of

overall metabolic energy requirements at high pressures.

Like all protobranchs, the yoldiellids have large eggs and

larval development is almost certainly short-lasting, non-

feeding and takes place close to the sea floor. Although there

are subtle basinal differences in shell form, some of which

may be sufficiently distinct to establish subspecies (e.g. Y.

obesa and Y. inconspicua) there is little doubt that either

widespread gene flow occurs and/or that genetic change is

slow. Clearly, the yoldiellid form is one that is extremely

successful. The subfamily contains by far the most species of

all the protobranch families and subfamilies.

Much of the scientific discussion on the distribution of the

Yoldiellinae will be incorporated into a following and final

round-up paper on the diversity and zoogeography of the

deep-sea protobranchs of the Atlantic. Nevertheless, because

it is such a large group, the distribution of the 29 species of

the genus Yoldiella described here reflect many of the general

features of protobranch distribution. Thus, of the 29 species

only a limited number can be regarded as being widespread

(Table 3). Only six species are present in five or more of the

Atlantic abyssal basins and of these, five are abyssal and one

is lower slope/abyssal rise in its depth distribution. There are

16 endemic species, of these five species and one subspecies

are restricted to the Argentine Basin. A further four endemic

species are found in the Cape or Angola Basins. Thus, it is

clear that most endemic species are in the South Atlantic.

Furthermore, the South Atlantic has been much less sampled

than the North and one would suspect that more rare

endemic species will be reported in the future. This is clearly

of considerable importance in speculations on the origin of

the protobranch fauna of the Atlantic. Although endemic

species are not restricted to upper slope depths, most of the

species at upper slope depths are endemic and those few that

are not, are restricted to the North European and North

American Basins. Thus, in general, the deeper the species

occurs, the more widespread is likely to be its distribution.

This may simply reflect the fact that the abyssal plains contain

enormous areas of sediment of similar characteristics and that

distribution simply reflects the commonality of the environ-

ment.

REFERENCES

Allen, J.A. 1992. The evolution of the hindgut of the deep-sea protobranch

bivalves. American Malacological Bulletin, 9: 187-191.

Allen, J.A. & Hannah, F.J. 1986. A reclassification of the Recent genera of the

sublass Protobranchia (Mollusca: Bivalvia). Journal of Conchology, 32:

225-249.

Allen, J.A. & Hannah F.J. 1989. Studies on the deep-sea Protobranchia. The

subfamily Ledellinae (Nuculanidae). Bulletin of the British Museum (Natural

History), Zoology, 55: 123-171.

Allen, J.A. & Sanders, H.L. 1973. Studies on the deep-sea Protobranchia, the

families Siliculidae and Lametilidae. Bulletin of the Museum of Comparative

Zoology Harvard, 145: 263-310.

Allen, J.A. & Sanders, H.L. 1982. H.L. Studies on the deep-sea Protobranchia.

The subfamily Spinulinae (family Nuculanidae). Bulletin of the Museum of

Comparative Zoology Harvard, 150: 1-30.

Allen, J.A. & Sanders, H.L. The zoogeography and diversity of the deep-sea

protobranch bivalves of the Atlantic (in m.s).

Clarke, A.H. Jr. 1963. Arctic archibenthal and abyssal mollusks. Two mollusks

dredged from drifting ice station Charlie (Alpha 2). Bulletin, National

Museum of Canada, 185: 90-109.

Jeffreys, J.G. 1876. Preliminary reports of the biological results of a cruise in

H.M.S. ‘Valorous’ to Davis Straits in 1875. Proceedings of the Royal Society

of London, 25: 177-237.

Jeffreys, J.G. 1879. On the Mollusca procured during the ‘Lightening’ and

‘Porcupine’ Expeditions 1868-1870. Part II. Proceedings of the Zoological

Society of London, 1879: 553-558.

Knudsen, J. 1970. The symstematics and biology of the abyssal and hadal

Bivalvia. Galathea Reports, 11: 241.

Locard, A. 1898. Mollusques Testaces. Expeditions Scientifiques du Travailleur

et du Talisman, 2: 1-515.

Ockelmann, K.W. 1955. The Zoology of East Greenland. Marine Lamellibran-

chiata. Meddelelser om Grenland, 122: 1-258.

Odhner, N.H. 1960. Mollusca. Reports of the Swedish Deep-Sea Expedition 2,

Zoology, (22): 367-400.

Rhind, P.M. & Allen, J.A. 1992 Studies on the deep-sea Protobranchia

(Bivalvia): the family Nuculidae. Bulletin of the British Museum (Natural

History), Zoology, 58: 61-93.

Sars, G.O. 1878. Bidrag til kundskaben om Norges artiske Fauna 1, Mollusca

regionis articae Norvegiae. 466 p. Christiana.

Sanders, H.L. & Allen, J.A. 1973. Studies on the deep-sea Protobranchia

(Bivalvia): Prologue and the Pristglomidae. Bulletin of the Museum of

J.A. ALLEN, H.L. SANDERS AND F. HANNAH

Comparative Zoology Harvard, 145: 237-261.

Sanders, H.L. & Allen, J.A. 1977. Studies on the deep-sea Protobranchia

(Bivalvia): the family Tindariidae and the genus Pseudotindaria. Bulletin of

the Museum of Comparative Zoology Harvard, 148: 23-59.

Sanders, H.L. & Allen, J.A. 1985. Studies on the deep-sea Protobranchia

(Bivalvia): the family Malletiidae. Bulletin of the British Museum (Natural

History), Zoology, 49: 195-238.

Shileiko, A.A. 1985. [The genus Yoldiella auct. as a combined group (Bivalvia,

Protobranchia)]. Transactions, P.P. Shirshov Institute of Oceanology, 120:

165-175.

Stasek, C.R. 1965. Feeding and particle-sorting in Yoldia ensifera (Bivalvia:

Protobranchia), with notes on other nuculanids. Malacologia, 2: 349-366.

Verril, A.E. & Bush, K.J. 1898. Revision of the deep-water Mollusca of the

Atlantic coast of North America with descriptions of new genera and species.

Part 1. Bivalvia. Proceedings of the U.S. National Museum, 20: 775-901.

Warén, A. 1978. The taxonomy of some North Atlantic species referred to

Ledella and Yoldiella (Bivalvia). Sarsia, 63: 213-219.

Warén, A. 1980. Marine Mollusca described by John Gwyn Jeffreys, with the

location of type material. Conchological Society of Great Britain and Ireland

Special Publication No. 1: 1-60.

Warén, A. 1989. Taxonomic comments on some protobranch bivalves from the

northeastern Atlantic. Sarsia: 223-259.

Bulletin of The Natural History Museum

Zoology Series

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No. 1 The Hemiuridae (Digenea) of fishes from the north-east

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Volume 52

No. 1 Miscellanea.

A revision of the genus Pseudovorticelia Foissner &

Schiffman, 1974 (Ciliophora: Peritrichida). A. Warren.

The taxonomic status of the genera Pontigulasia,

Lagenodifflugia and Zivkovicia (Rhizopoda:

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A revision of the foraminiferal genus Adercotryma

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Hermit crabs associated with the bryozoan Hippoporidra

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The first zoea of three Pachygrapsus and of Cataleptodius

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A classification of the phylum Sipuncula. P. E. Gibbs &

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Two new species of Garra (Teleostei: Cyprinidae) from

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Notes on Atlantic and other Asteroidea 5.

Echinasteridae. Ailsa M. Clark.

Observations on the marine nematode genus Spirina

Gerlach, 1963 (Desmodoridae: Spiriniinae) with

descriptions of two new species. J. W. Coles.

Caleupodes, a new genus of eupodoid mite (Acari:

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The Barbus perince—Barbus neglectus problem and a

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No. 4 Certain Actiniaria (Cnidaria, Anthozoa) from the Red

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1987. Pp. 205-292. £23.95

Volume 54

No. 1 The cranial muscles and ligaments of macrouroid fishes

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No. 2 A review of the Macrochelidae (Acari: Mesostigmata) of

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A review of the Copepod endoparasites of brittle stars

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A new genus of tantulocaridan (Crustacea:

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Unusual ascothoracid nauplii from the Red Sea. G. A.

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New nicothoid copepods (Copepoda:

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A new genus of Lichomolgidae (Copepoda:

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Volume 55

No. 1 Miscellanea.

Structure and taxonomy of the genus Delosina Wiesner,

1931 (Protozoa: Foraminiferida). S. A. Revets.

Morphology and morphogenesis of Parakahliella haideri

No. 2

nov. spec. (Ciliophora, Hypotrichida). H. Berger & W.

Foissner.

Morphology and biometry of some soil hypotrichs

(Protozoa, Ciliophora) from Europe and Japan. H.

Berger & W. Foissner.

Polyclad turbellarians recorded from African waters. S.

Prudhoe, O.B.E.

Ten new taxa of chiropteran myobiids of the genus

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Anatomy and phylogeny of the cyprinid fish genus

Onychostoma Gunther, 1896. C. Yiyu. 1989. Pp.

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Studies on the Deep Sea Protobranchia: The Subfamily

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Volume 56

No. 1

No. 2

Osteology of the Soay sheep. J. Clutton-Brock, K.

Dennis-Bryan, P. L. Armitage & P. A. Jewell.

A new marine species of Euplotes (Ciliophora,

Hypotrichida) from Antarctica. A. Valbonesi & P.

Luporini.

Revision of the genus Eizalia Gerlach, 1957 (Nematoda:

Xyalidae) including three new species from an oil

producing zone in the Gulf of Mexico, with a discussion

of the sibling species problem. D. Castillo-Fernandez &

P. J. D. Lambshead.

Records of Nebatia (Crustacea: Lepostraca) from the

Southern Hemisphere a critical review. Erik Dahl.

1990. £31.00

Tinogullmia riemanni sp. nov. (Allogromiina:

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Larval and post-larval development of Anapagurus

chiroacanthus (Lilljeborg, 1855) Anomura: Paguroidea:

Paguridae. R. W. Ingle.

Redescription of Martialia hyadesi Rochebrune and

Mabille, 1889 (Mollusca: Cephalopoda) from the

Southern Ocean. P. G. Rodhouse & J. Yeatman.

The phylogenetic relationships of salmonoid fishes. C. P.

J. Sanford.

A review of the Bathygadidae (Teleostei: Gadiformes).

G. J. Howes & O. A. Crimmen. 1990. £36.00

Volume 57

No. 1

No. 2

Morphology and biometry of twelve soil testate amoebae

(Protozoa, Rhizopoda) from Australia, Africa and

Austria. G. Liiftenegger & W. Foissner

A revision of Cothurnia (Ciliophora: Peritrichida) and its

morphological relatives. A. Warren & J. Paynter

Indian Ocean echinoderms collected during the Sinbad

Voyage (1980-81): 2. Asteroidea. L. M. Marsh & A. R.

G. Price

The identity and taxonomic status of Tilapia arnoldi

Bilchrist and Thompson, 1917 (Teleostei, Cichlidae). P.

H. Greenwood

Anatomy, phylogeny and taxonomy of the gadoid fish

genus Macruronus Gunther, 1873, with a revised

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The pharyngobranchial organ of mugilid fishes; its

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taxonomic utility. I. J. Harrison & G. J. Howes

Cranial anatomy and phylogeny of the South-East Asian

catfish genus Belodontichthys. G. J. Howes & A.

Fumihito

A collection of seasnakes from Thailand with new

records of Hydrophis belcheri (Gray). C. J. McCarthy &

D. A. Warrell

The copepod inhabitants of sponges and algae from

Hong Kong. S. Malt

The freshwater cyclopoid of Nigeria, with an illustrated

key to all species. G. A. Boxshall & E. I. Braide

A new species of Ferdina (Echinodermata: Asteroidea)

from the Sultanate of Oman with discussion of the

relationships of the genus within the family

Ophidiasteridae. L. M. Marsh & A. C. Campbell £38.50

Volume 58

No. 1

No. 2

The morphology and phylogeny of the Cerastinae

(Pulmonata: Pupilloidea). P. B. Mordan

A redescription of the uniquely polychromatic African

cichlid fish Tilapia guinasana Trewavas, 1936. P. H.

Greenwood

A revision and redescription of the monotypic cichlid

genus Pharyngochromis (Teleostei, Labroidei). P. H.

Greenwood

Description of a new species of Microgale (Insectivora:

Tenrecidae) from eastern Madagascar. P. D. Jenkins

Studies on the deep-sea Protobranchia (Bivalvia): the

family Nuculidae. P.M. RhindandJ. A. Allen £40.30

Notes on the anatomy and classification of ophidiiform

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Acanthonus Ginther, 1878. G. J. Howes

Morphology and morphogenesis of the soil ciliate

Bakuella edaphoni nov. spec. and revision of the genus

Bakuella Agamaliev & Alekperov, 1976 (Ciliophora,

Hypotrichida). W. Song, N. Wilbert and H. Berger

A new genus and species of freshwater crab from

Cameroon, West Africa (Crustacea, Brachyura,

Potamoidea, Potamonautidae). N. Cumberlidge and P.

F. Clark

On the discovery of the male of Mormonilla Giesbrecht,

1891 (Copepoda: Mormonilloida) R. Huys, G. A.

Boxshall and R. Bottger-Schnack £40.30

Volume 59

No. 1

No. 2

A new snake from St Lucia, West Indies. G. Underwood

Anatomy of the Melanonidae (Teleostei: Gadiformes),

with comments on its phylogenetic relationships. G. J.

Howes

A review of the serranochromine cichlid fish genera

Pharyngochromis, Sargochromis, Serranochromis and

Chetia (Teleostei: Labroidei). P. H. Greenwood

A revision of Danielssenia Boeck and Psammis Sars with

the establishment of two new genera Archisenia and

Bathypsammis (Harpacticoida: Paranannopidae). R.

Huys and J. M. Gee.

A new species of Syrticola Willems & Claeys, 1982

(Copepoda: Harpacticoida) from Japan with notes on the

type species. R. Huys and S. Ohtsuka

Erratum £40.30

The status of the Persian Gulf sea snake Hydrophis

lapemoides (Gray, 1849) (Serpentes, Hydrophiidae). A.

Redsted Rasmussen.

Taxonomic revision of some Recent agglutinated

foraminifera from the Malay Archipelago, in the Millett

Collection, The Natural History Museum, London. P.

Bronnimann and J. E. Whittaker.

Foregut anatomy, feeding mechanisms, relationships and

classification of the Conoidea

(=Toxoglossa)(Gastropoda). J. D. Taylor, Y. I. Kantor

and A.V. Sysoev. 1993. Pp. 97-170. £40.30

Volume 60

No. 1

A new subfamily and genus in Achatinidae (Pulmonata:

Sigmurethra). A. R. Mead.

On Recent species of Spiraserpula Regenhardt, 1961, a

serpulid polychaete genus hitherto known only from

Cretaceous and Tertiary fossils. T. Gottfried Pillai and

H.A. Ten Hove. 1994. Pp. 1-104. £40.30

Phylogenetic relationships between arietellid genera

(Copepoda: Calanoida), with the establishment of three

new genera. S. Ohtsuka, G. A. Boxshall and H. S. J.

Roe. 1994. Pp. 105-172. £40.30

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