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(jtJ^^San Diego Society of Natural History

Founded 1 874

Number 7

July 1991

Remipedia

Part 2

Paleontology

Michael J. Emerson* and Frederick R. Schram

Natural History Museum of Las An^^eles County, 900 E.xposilion Blvd.. Los Aiii;eles. California 90007

ABSTRACT. — Five reeently collected specimens of llie Late Mississippian arthropod Tesniisocuris i;olilichi Brooks, 1955, from the Tesnus

Formation in Brewster County, Texas, are described, and the holotype is reexamined. Three of the new specimens and the holotype provide details

hitherto unknown and allow the first complete reconstruction of the animal to be made. The new specimens are interpreted as juveniles of the species,

which otherwise is known only from the adult holotype. The cephalic appendages are shown to resemble those of the living order Nectiopoda

(Crustacea: Remipedia). The specialized grappling mouthparts are characteristic of the class and confirm the status of the fossil order Enantiopoda

as a sister group of the Nectiopoda. The trunk appendages of the fossil species, though resembling those of the nectiopodans in certain respects, differ

fundamentally in structure and probable function from those of any other crustacean. Each trunk segment is shown to bear a homonomous .series of

two pairs of uniramous, paddle-shaped limbs, a condition we term duplopody (in clear distinction to diplopody seen in uniramians) rather than the

single pair of biramous appendages characteristic of the Nectiopoda. We have found it necessary to coin additional terminology to describe

Tesnusocaris. The ventrolateral series of limbs, or exopedes, apparently functioned as oars in rowing, but the midventral series of appendages, or

endopedes, probably functioned as hydrofoils in a unique form of sculling. The duplopodous condition of Tesnusocaris is compared to the seg-

mentation patterns of other articulates. The morphology of the trunk segments is not adequately described by the existing concepts of limb

homology. Other fossil remipedes are considered, and other possible instances of duplopody in the fossil record are examined.

INTRODUCTION

The problematic arthropod Tesnusocaris i;oldichi Brooks, 1935,

was originally collected by S. S. Goldich (pronounced goal-dick) in

1939 and was the only identifiable macrofossil specimen found in

the Tesnus Formation in the southeastern comer of the Marathon

Uplift in western Texas. The calcareous shales from which the

fossil came have been assigned to the Mississippian-Pennsylvanian

boundary. Brooks (1955) described the specimen in a paper illus-

trated with a generalized reconstruction and beautifully detailed

photographs. Brooks was uncertain of the taxonomic position of

this species and consequently used neutral anatomical temis to

describe the specimen. He tentatively allied the fossil with the

Cmstacea and compared it to all major crustacean groups. In the

text of the paper. Brooks placed Tesnusocaris closest to the

Anostraca, but in a footnote added in press he compared the speci-

men to the then newly described cephalocarids. Birshtein (1960)

accepted the latter assignment and proposed for Tesnusocaris the

order Enantiopoda. which he viewed as related to the order

Brachypoda (Birshtein's ordinal name for the living

Cephalocarida). Hessler (1969) rightly rejected the suggested

cephalocarid affinities of the Texas fossil, and Moore (1969) as-

signed it an uncertain status within the Malacostraca. Most subse-

quent authors who dealt with Tesnusocaris at all have placed it

within the Branchiopoda. Bergstrom (1979) suggested that the

fossil was that of a uniramian, and Schram (1982) voiced uncer-

tainty about the fossil's crustacean affinities.

The situation changed with the discovery of the living repre-

sentatives of the Class Remipedia (Yager 1981 ). These creatures are

found in anchialine caves in the West Indies, Yucatan, and the

Canary Islands (Schram et al. 1986, Yager 1987a.b, Yager 1989).

The animals possess a combination of many of the primitive fea-

tures that arthropod phylogeneticists had predicted would be found

in an ancestral cmstacean type (e.g., Hessler and Newman 1975.

Schram 1982). though the feeding appendages are rather special-

ized. These plesiomorphic characteristics include a trunk that is not

regionalized, a pair of appendages on every body segment, each

trunk limb with a biramous fomi. no carapace extending back from

the head, and serial homonomy in intemal organ systems. The

living remipedes were later sequestered (Schram 1986) into their

own order. Nectiopoda. distinct from the fossil Enantiopoda. Cer-

tain features present in the nectiopodans, such as the headshield and

long unregionalized trunk, were also noted in Tesnusocaris. This

prompted Schram (1983) to suggest that the living remipedes and

'Deceased, March 22, 1990.

M. J. Emerson and F. R, Schram

LIST OF ABBREVIATIONS AND KEY

Sb - sternal bar

SDSNH - San Diego Society of Natural History

T - tergite

USNMP - United States National Museum

(Paleontology)

V - ventral

Vis - ventrolateral sclerite

X - exopede

Xp - exopod

.4 - fourth podite of limb or ramus

? - identification imcertain

( ) - estimated position of insertion of limb

-, — I — |- - microescarpment, hatch marks point to

lower level [reversed from couterpart]*

-P -r -r - rounded microescarpment [hidden or

deemphasized; reversed from

counterpart]*

- clearly defined boimdary

indistinct boundary [hidden or

deemphasized boundary]*

faint boundary [deemphasized

boundary]*

|i|i|f - shaded area keyed to caption

::::■:•:■:;:•: - stippled area keyed to caption

!^!^!^^ - lined area keyed to caption

additional attributes of partly

reconstructed version in brackets

Remipede Paleontology

the Enantiopoda might be related. This possibility was strengthened

by a reexamination of the holotype {Schram et ai. 1986), then the

only known specimen of Tesnnsocaris. The new study indicated that

rather than the setose, filtering mouthparts reconstructed by Brooks

(1955), the Texas fossil actually had robust, spinose mouthparts.

The recent remipedes appear to be very specialized carnivores

(Schram and Lewis 1989), and it seemed possible from study of the

TesniiSDCiuis holotype that the Texas form also may have been

highly adapted to active predation.

Considering the obvious potential importance of Tesnnsocaris

and the limited value of the single known specimen, we decided to

relocate the locality where Goldich collected the type (Brooks

1955). This was done in the fall of 1985, and five new specimens

were found (Schram and Emerson 1986). One specimen is excep-

tionally well preserved throughout nearly its entire length, and two

more specimens provide certain details lacking from the others. The

two remaining specimens, because of their uniformly poor preser-

vation, can be assigned to this species only by analogy with the

other fossils. Along with a restudy of the holotype, the new fossils

allow the first complete reconstruction of T. goldichi. one that dif-

fers significantly from previous interpretations.

A reexamination of the holotype and study of some newly

discovered specimens of Cryptocaris hootchi Schram, 1974, from

the Mazon Creek faunas of Illinois, Middle Pennsylvanian, reveal

that this species is not a tanaidacean as originally thought but is

related to Tesnnsocaris.

LOCALITY AND STRATA

Locality. — The holotype specimen of Tesnnsocaris goldichi.

USNMP 124173. was originally collected in 1939 by S. S. Goldich

of the University of Minnesota while engaged in a geological field

survey of the southeastern Marathon Basin. The specimen was

deposited in the U.S. National Museum and eventually was named

and described by H. K. Brooks ( 1955). At that time the type locality

(Fig. 1 ) was recorded merely as "west of Rough Creek, 4,300 ft. S

51 E of Hill 4334 in the northwestern comer of the Dove Mountain

quadrangle, Brewster Co. Texas" (Brooks 1955:855).

Our 1985 expedition (Schram and Emerson 1986) precisely

located the type locality. SDSNH locality number 3307. Its UTM

coordinates are 69478/331915 on the Pine Mountain West, Texas,

7.5' USGS quadrangle (1983 edition): 29°59'23"N, 102°58'52"W

^ta6ttkiiMiib_^

Figure 1 . View looking northeast from the entry road to Rough Creek

Ranch. Brewster Co.. Texas. Arrow points to approximate location of lo-

calities for Tesnnsocaris goldichi on the eastern flanks of Hill 4334.

Figure 2. The 1939 type locality of S. S. Goldich for Tesnnsocaris

goldichi. Rough Creek Ranch, Brewster Co., Texas. A. overview of SDSNH

locality number 3307; B. closeup view of outcrop.

(Fig. 2). No additional specimens were collected at this site, but a

second locality did produce three fossiliferous concretions that

contained Tesnnsocaris. This locality. SDSNH 3308. lies at UTM

coordinates 69465/331905 on the Pine Mountain West, Texas, 7.5'

quadrangle (1983 edition): 29°59'I9"N, 102°58'55"W (Fig. 3).

These disjunct outcroppings of the distinctive fossiliferous shale lie

on either side of a saddle ridge that links Hill 4334 to Hill 3605

southeast of it.

Our study area is located in the southeast quarter of the Mara-

thon Basin on the Rough Creek Ranch (referred to on some old

maps as the Gage Ranch or the western portion of the old San

Francisco Ranch). This ranch is situated approximately 25 miles

east of Texas Highway 343 south of Marathon, Texas, an hour-and-

a-half journey on a private dirt road that extends into an area

southeast of Hell's Half Acre.

Regional Geology. — The geology in the area of immediate

concern is dominated by the Tesnus Formation, a name derived

from an inversion of the word "sunset" applied to Tesnus Station, a

siding on the Southern Pacific Railroad east of Marathon. The

geologic formation was named by Baker and Bowman (1916),

though the most thorough review of the geology of the region is that

of King ( 1937). In the northwestern part of the Marathon Basin, the

upper part of the Tesnus is about 300 ft. thick and composed of

black shales and some sandstones. In the southeastern part of the

basin, including our study area, the lower ponion of the Tesnus is

approximately 6500 ft. thick and composed of alternating reddish

M. J. Emerson and F. R. Schram

Figure 3. The 1985 locality discovered by M. J. Emerson for

Tesmisocaris f;olJichi. Rough Creek Ranch, Brewster Co., Texas. A, over-

view of SDSNH locality number 3308; B, closeup view of outcrop.

brown sandstone and gray-green shales deformed into nearly verti-

cal layers (King 1930). The more resistant sandstones form cocks-

comb ridges, and the softer shales erode to form valleys. The Tesnus

overlies the Caballos Novaculite, a very resistant cherty Devonian

formation.

Along Rough Creek, the Caballos crops out about one mile

above the junction with San Francisco Creek (see Schram and

Emerson I9S6 for details of the geography of the area). At this

point, the Caballos is overlain with green shales of the Rough Creek

Member that weather to a dark gray. The lower part of these beds is

almost entirely shale, with an occasional interbedding of thin sand-

stone. The sandstones become more abundant and thicker toward

the top of this member. Farther west along the road that leads to

Rough Creek Ranch, at Indian Creek Ranch, the Caballos is over-

lain by a rather argillaceous sandstone, and the most basal shale

beds that are seen along Rough Creek are missing.

The beds from which Te.sniisocciris fioUlichi was collected are

sandwiched between two prominent sandstone layers. The Tesnus

Fonnation in that part of the Rough Creek valley is thick but was

not measured fully by us since it forms a cliff on the eastern and

southeastern flanks of Hill 4334. However, the beds immediately

below the cliff in which the fossils were collected were more

accessible and measured top to bottom as follows:

Bed 6. Poorly bedded, greenish shale 0.36 m

Bed 5. Finely bedded, blue-gray fissile shale, with scattered

concretions 6.1 m

Bed 4. Green-to rust-colored shale with very disturbed and reworked

bedding, large calcareous concretions common 5.2 ni

Bed 3. Greenish shale, poorly bedded 1 1 .0 m

Bed 2. Greenish gray shale, finely bedded 13.6 m

Bed 1. Sandstone 2.0 m

The concretions with the remipede fossils were collected in situ

from Bed 5 (Fig. 2B), which is identified readily by its distinctive

blue-gray color. Four medium-sized concretions were collected,

only three of which contained fossils. A fifth concretion, very large

and badly fragmented, was noted in the field but was not collected

since it did not appear to contain any recognizable fossil material.

Strali graphic Correlation. — The stratigraphic correlation of the

Tesnus long has been a problem. Northwest of our localities, the

Upper Tesnus crops out in regions called HelPs Half Acre and the

Devil "s Backbone, though we did not investigate these areas. The

Tesnus there is said to resemble closely in appearance the Jackfork

Sandstone in the Ouachita Mountains of Oklahoma. Mapel el al.

(1979) pointed out that the regional stratigraphy of the Trans-Pecos

indicates that the unconformity of the Tesnus and the underlying

Devonian Caballos is a gap representing at least a part of the

Kinderhookian time of the Mississippian.

In addition to Tesnusocaris. most of the fossils collected in the

Tesnus itself have been reported in the upper beds of the formation.

Baker and Bowman ( 1916) listed a Pennsylvanian-type fauna col-

lected from sites west and northwest of Marathon that includes a

wide array of brachiopods, plants, bryozoans. fusilines, and crinoid

stems. The best analysis of floral fossils is King's ( 1930, 1937). The

following plants occur approximately 10 miles southwest of Mara-

thon: Newopieris and Alelhopteris leaves: parts of Clamites. Slig-

maria, and Asterophyllites; and Lepidodendron, Artesia, Cordaites.

Cardiocarpon. and Trigonocarpon. This flora indicates a Pennsyl-

vanian. Middle Pottsville age. A smaller flora collected south of

Tesnus Station consists of tips of leaflets of either N. giganlea or N.

capilala, which does not contradict the Pottsville assignment.

Other fossils in the Upper Tesnus are less helpful in determining

the age of the strata (King 1937). Fusilinid foraminiferans have

been collected approximately 18 miles east of Marathon. These

apparently indicate a lowemiost Pennsylvanian age for the upper

member, since they are equivalent to forams found in the Caney

Shale of Oklahoma. Apparent monaxon sponge spicules have been

found in the calcareous sandstones on the north slope of West

Bourland Mountain south of Marathon, just below the plant hori-

zon. These cibjects, however, are black and appear to be phosphatic

rather than siliceous. We noted similar objects in some of the shale

beds along Rough Creek immediately above the novaculite, and we

concluded that these were mineral inclusions in the shale.

Although the upper part of the Tesnus Formation has been

dated reliably, the age of the more than 6000 feet that are below

Remipede Paleontology

the upper member is less certain (Maxwell et al. 1967). King

(1937) equated the Tesnus with the Stanley, Jackfork, and

Springer formations of Oklahoma and Arkansas, which date from

the Upper Mississippian. Crosby and Mapel ( 1975) stated that the

Mississippian-Pennsylvanian boundary probably was located

high in the Tesnus. Jones (1953) believed that the Rough Creek

member was the approximate equivalent of the early Mississip-

pian Stanley Formation. Hass (1956) felt that the conodonts of

the Stanley were early or middle Meremecian Mississippian in

age. and Elias (1959) believed that the conodonts in the lower

part of the Stanley were early Mississippian. Only Ellison ( 1962)

reported collecting conodonts from the Lower Tesnus itself, and

he felt that they indicated a Mississippian age. We collected a

single HindciKlella (SDSNH 29714) in a concretion from the

beds just below those containing the crustaceans, which is con-

sistent with a Carboniferous age but not more explicit than that.

More recently. Mapel et al. (1979) equated the Tesnus with the

Stanley and concluded that the Lower Tesnus is Mississippian

Interval D, i.e., uppermost Meremec, or Chester. It appears that

Tesnusocaris is most likely Upper Mississippian in age.

Paleoenvironment. — King (1930) equated the Tesnus to the

Chester-age Helms group of the Hueco Mountains at the western tip

of Texas near El Paso. These latter beds thicken to the southeast,

toward the Tesnus Formation, which suggested to King that the

Tesnus represents thicker geosynclinal deposits in that region. This

opinion was shared by Mapel et al. (1979), who felt that the Stanley

and Tesnus formations represent rapidly sinking geosynclinal

deposition. King ( 1937). however, concluded that the Tesnus might

represent shallow marine, deltaic, or even continental deposits. The

massive shales and interbedded sandstones characteristic of the

Tesnus were viewed (Crosbey and Mapel 1975) as deep-water

deposits into which clastic sediments were swept off the Carbonif-

erous shelf by turbidity currents (Flawn et al. 1961 ).

Dutro et al. ( 1979) indicated that the Mississippian paleogeog-

raphy of the area included a highland that extended across what is

now northern Mexico and southern Texas and was continuous to the

northeast with the Appalachian Mountains. The offshore Ouachita

Trough, into which the Tesnus sediments were deposited in this

interpretation, extended from the Oklahoma region to the Trans-

Pecos. Dutro et al. (1979) believed that the continental source of the

marine sediments during Tesnus times came from the southeast

with the Tesnus Formation apparently the result of deposition in a

relatively deep sea. However, turbidity deposits in deep troughs are

not noted especially for good fossil preservation. This may stem

from the general paucity of life forms in deep-sea environments,

coupled with a low rate of fossil preservation in such habitats

characterized by coarse clastic sediments. Therefore, the interpreta-

tion of Dutro et al. (1979) may explain why the Tesnus Formation,

especially the lower member, is so poor in fossils. Tesnusocaris

goldichi occurs in an unlikely paleontological setting, and the fact

that we have good material of this soft-bodied animal is all the more

exceptional.

The fossils are enclosed in claystone concretions that are com-

posed largely of phyllite and montmorillinite. Ferromagnesium

minerals consist of hornblende altered to sauserite (albite and epi-

dote) with some traces of biotite. There is no calcite as cement,

although there are traces of calcium sulfate. Apparently the con-

cretions were cemented by compaction and alteration of the clay

minerals (William Estavillo, personal communication).

MATERIALS AND METHODS

The study of Tesnusocaris is limited by the small number of

available specimens and their generally poor preservation. There is

wide variation in size between specimens as well as in their

preserved orientations. All these factors contribute to the difficulty

of correlating features observed on individual specimens. To derive

the maximum information from each speciinen, we made detailed

camera lucida drawings that incorporated observations made under

a variety of conditions of immersion, illumination, and magnifica-

tion. The drawings were then rigorously cross-checked and com-

bined to produce Figures 4, 10, 12, and 14. Each figure presents

unreconstructed views of the most informative specimens (includ-

ing the counterpart, where applicable) associated with a partly

reconstructed, composite view that is labeled.

The precise orientation of each concretion with respect to the

depositional interface was not noted in the field. Such knowledge

would have proved to be important for interpreting the fossils, since

only one-half of the concretion affords a "normal" view of the

specimen as it originally lay on the ancient bottom, i.e., dorsal,

ventral, or lateral side up. Diagenetic flattening and distortion can

be understood accurately only if the original direction of gravita-

tional forces is known. This information is also crucial in deter-

inining the spatial relationships of structures preserved on the op-

posing sides of the split concretion. Our determination of which

side of the concretion afforded the normal surface view (henceforth

referred to as the "part") and which one needed to be flipped to

conform to the normal view (henceforth the "counterpart") was

made by an examination of microescarpments on the fossil surfaces

that indicate the overlap of structures such as legs (Whittington

1971 ). Since the part and counterpart were drawn separately under

the camera lucida and composite views then generated, minor

differences in the depiction of certain details between the

uncomposited and partly reconstructed views have occurred, but

these were not significant. No attempt was made to revise the

uncomposited views to make them conform to subsequent inter-

pretations, with one exception which will be duly noted.

The uncomposited drawings are the principal raw data we used

in this study, since most of the specimens could not be understood

fully from a direct examination of the fossils alone. Those drawings

are presented here, unencumbered by the labels that accompany the

reconstructed composite view, to allow the reader to examine the

spatial relationship of the part and counterpart and to permit an

independent assessment of the evidence used to support our inter-

pretations. Through this process, we have striven to make the best

use of the imperfect material at hand without overextending the

powers of interpretation. In all instances, "left" and "right" refer to

the bilateral symmetry of the animal as shown in the composite

(labeled) view. In contrast, "above" and "below" refer to the per-

spective of the viewer, who is assumed to be above the specimen

with respect to its original orientation on the depositional interface,

as shown in the composite view.

SYSTEMATICS

Class REMIPEDIA Yager, 1981

Diagnosis. — Crustaceans without trunk tagmosis or clearly de-

veloped carapace and possessing large, grappling mouthparts.

Subrectangular headshield with anterior, lobate projection and cer-

vical groove; antennules large and biramous: protopod indistinctly

divided into two segments, the proximal one with aesthetascs, the

distal one bifurcate (?); dorsal ramus larger than ventral ramus and

consisting of more numerous segments, ventral ramus consisting of

twelve or fewer long segments in known species, with short, mar-

ginal setae. Antennae biramous. Setose paddles, modest in size,

consisting of an anteriorly directed slender protopod of two seg-

ments, the second bearing an unsegmented exopod laterally and

distally supporting an endopod of three (?) segments arching

anterolaterally. Labrum subtriangular. large, and bulbous, at least

M. J. Emerson and F. R. Schram

partially enclosing mandibles within atrium oris (entognathy ). Man-

dibles well developed, supporting a large, spinose molar process

and a small lacinia mobilis (?), lacking palps. Maxillules uniramous.

subchelate, with seven segments, spinose basal endites, and termi-

nal fang; robust first endite with at least seven stout spines directed

toward mouth. Ma.xillae uniramous, subchelate, with spinose basal

endites, including a tripartite first endite and terminal claw. First

trunk somite as maxillipedal segment fused to cephalon;

maxillipedes uniramous, subchelate. with terminal claw. Trunk with

numerous segments, each bearing a homonomous series of setose

swimming appendages; anal segment bearing caudal rami.

Remarks. — This diagnosis includes several characters previ-

ously known only from the Nectiopoda (Schram et al. 1986) but

now confirmed for the Enantiopoda as well. Chief among these are

the details of mouthpart structure and the presence of caudal rami.

Order NECTIOPODA Schram 1986

Diagnosis. — Remipedes lacking pigment and eyes. Cephalon

with ventral, spined frontal processes. Antennular aesthetascs with

long ribbonlike setae covering antennae; dorsal ramus with several

long segments, fewer than twenty in known species. Antennae with

long, plumose setae; endopod segmentation complete. Maxillules

apparently hypodermic, with subterminal pore on fang connected

by duct to glandular tissue. Maxillae and maxillipedes with fewer

than nine distinct podomeres in known species. Each trunk segment

bearing one pairof biramous limbs, each with a large ventrolaterally

directed protopod distally supporting two oar-shaped rami of three

(exopods) or four (endopods) elliptical segments with rounded tips

and moderate to long marginal setae. Hermaphrodites with gonop-

ores located on bases of eighth (female) and fifteenth (male) trunk

limbs. Anal segment with one pair of short, simple caudal rami; gut

with metameric diverticulae.

Remarks. — This diagnosis is included here to revise that given

by Schram etal. (1986) in light of the revised diagnosis for the class

given above. Several of the characters probably pertain to the class

as a whole, though their presence in the fossil Enantiopoda cannot

be confirmed at this time. The most important of these are the

maxillulary fang's being hypodermic, the location of the gonopores

(the maxillipedal segment is counted as the first trunk somite), the

metameric gut diverticulae. and possibly the frontal processes. The

most reliable and significant characters distinguishing this order are

the lack of eyes, the long segments of the antennular dorsal ramus,

the biramous trunk limbs with similar oar-shaped rami, and the

relatively short and simple pair of caudal rami.

Order ENANTIOPODA Birshtein. 1960

Diagnosis. — Anterior headshield bearing a set of large, sessile

compound eyes ('?); frontal processes unknown; dorsal ramus of

antennules finely annulate; mandibles not completely enclosed

within atrium oris by labrum. Trunk segments duplopodous. each

bearing two pairs of uniramous appendages; anal segment with two

pairs of long, uniramous, annulate caudal rami.

Remarks. — The nature of the eyes is unresolved at this time

because, although they are very evident on specimens of

Tesnusocaris goldichi, the eyes are not clearly preserved on any of

the specimens at hand oi Cryptocaris hootchi.

Family TESNUSOCARIDIDAE Brooks, 1955

Diagnosis. — Since there is only one family recognized at this

time, the diagnosis is the same as that of the order.

Type species. — Tesnusocaris goldiclii Brooks, 1955.

Genus TESNUSOCARLS Brooks, 1955

Diagnosis. — .Adult at least 9.5 cm in total body length.

Headshield expanded with length approximately equal to width,

panially covering cephalic appendages laterally and first two (?)

trunk tergites posteriorly. Trunk with at least 21 tergites; limbs

gradually diminishing posteriorly.

TESNUSOCARIS GOLDICHI Brooks. 1955

Diagnosis. — Antennulary aesthetascs bearing relatively short

setae; dorsal ramus of antennules with more than 100 short annulae

without setae. Marginal setae of antenna relatively short, antenna!

endopod with incomplete segmentation. Incisor process of man-

dible unknown; maxillae and maxillipedes with nine podomeres.

Mesial trunk limbs (endopedes) developed as flippers including a

bell-shaped coxa equally broad as long, a marginal crest laterally,

short marginal setae medially, and nine podomeres with the most

distal podomere acute. Lateral trunk limbs (exopedes) developed as

oars including a bell-shaped coxa broader than long, moderately

long marginal setae, and five podomeres with the most distal

podomere oval.

Juveniles approximately 2.5-4.0 cm in total body length, not

including caudal rami. Headshield small, not covering cephalic

appendages laterally or first tergite posteriorly; width exceeding

length. Trunk with approximately twelve tergites; most trunk limbs

equal in size.

Holotxpe. — USNMP 124173, concretion with counterparts.

Otiier Malerial.~?,DSn\\ 28251a,b,c 28252, 2825.3, concre-

tions with counterparts.

Type Locality.— 29°59'2rN, 102°58'52" (grid coordinates

69478/331915); west of Rough Creek; 4300 ft. S, 51 ft. E of Hill

4334, Dove Mountain Quadrangle, Brewster County, Texas (Fig.

2A, B).

Stratum. — Tesnus Formation. Upper Mississippian.

Remarks. — This diagnosis expands considerably on those by

Brooks (1955). Schram et al. (1986), and Schram (1986). These

earlier works were based entirely on the incomplete holotype of T.

goldiclii and did not describe the dorsal ramus of the antennule. the

protopod and exopod of the antenna, the base of the mandible, the

rami of the maxillule, maxilla, and maxillipede. all but the distal

end of the exopede, ventral scleriles, the caudal rami, and juveniles.

Our understanding of the fundamental structure of nearly all previ-

ously described appendages has been completely revised.

We believe it necessary to provide detailed descriptions of the

individual specimens given the controversial nature of the anatomy

of this species as well as to provide the details concerning the

changes we have made in previous descriptions of this T. goldiclii.

Very little has been retained from previous works, aside from the

overall form of the species.

Description. — The following examination of the available fos-

sils uses the conventions established under Materials and Methods.

SDSNH 28252 (Figures 4-8)

The concretion that this specimen occupies was found //; situ

near the top of the shale bed. When first cracked open with a

hammer, the concretion split so that very little of the animal was

exposed on both the part and counterpart (Fig. 4B, shaded area).

Subsequent preparation of the part revealed a nearly complete,

well-preserved, juvenile individual. The overall body shape and

arrangement of limbs indicate a position at burial with the animal

resting somewhat obliquely on its left ventral surface, exposing

most of the appendages of the right side, and exhibiting little

distortion except flattening (Fig. 5).

The most anterior part of the headshield is poorly preserved.

The counterpart presents an isolated fragment of the posteromedial

Reniipede Paleontology

Table 1. Measurements of Tesnusocaris goktichi specimens ni mm. Antennule length for USNMP 124173 is for the ventral branch;

antennule length for SDSNH 28852 is for the dorsal branch.

Specimen Head length Head width

Length of Trunk

Body length A 1 length caudal rami Tl length T2 length T3 length segment no.

USNMP

124173

SDSNH

28851a

SDSNH

28851b

SDSNH

28852

19.7

4.3

=5.6

7.3

16.5

4.7

5.4

=7.0

82.6+

=25.5

31.0

58.4

18.0+

0.95

1.3

1.8

22+

13

12

portion of the anterior headshield lobe. On the part, a tenuous

outline of the anterior headshield is preserved and is slightly more

defined at the right margin, where a faint suggestion of facets may

indicate the right eye (Fig. 4B. RE?). An area at the left edge of

what appears to be the anterior headshield (Figs. 4B, 6A, AHS?)

alternatively might be part of the left antennule.

The part reveals much of the head. The flagellum of the dorsal

ramus of the right antennule (RAID) is poorly preserved on both

part and counterpart, but the left dorsal ramus (Fig. 4B, LAID) is

clearly preserved (Fig. 6A). Four segments (.1-.4) appear to consti-

tute the large peduncle, though the first segment may be the dorsal

bifurcation of the protopod as it appears in the Nectiopoda (Fig.

23 A). An apparent arthrodial membrane between the third and

fourth segments may represent an additional podomere. The pe-

duncle supports a distinctive flagellum on which at least 100

annulated joints are well preserved. The annulations are quite dis-

tinct, with the distal edges free from subsequent rings. A slight, but

distinct, medial ridge extends the length of the flagellum on the

dorsal surface. No clear indication of setae is visible, though faintly

preserved annular divisions of the right ramus lateral to the dorsal

ridge have the appearance of setae. The left flagellum tapers only

slightly along its considerable length, and was apparently much

longer than the body. The ventral ramus is not clearly preserved but

may be present in the confusion of features at the lateral edges of

the headshield. especially on the left side.

The main part of the headshield is well preserved only at the

anterior and posterior edges and the right posterolateral comer. The

overall shape is rectangular, with length slightly exceeded by width.

A number of confusing features evident in this area may represent

dorsal furrows or ventral structures impressed from beneath. The

right side of the cephalon is completely exposed, though structures

in this area are poorly defined and appear to have been shifted to the

right. The headshield is flexed ventrad slightly in relation to the

trunk, despite dorsoventral flattening of the entire specimen.

No clear preservation of antennae, labrum, or mandibles is

present. A small, faint object (LM?) appears dark under alcohol

immersion at high magnification (lOOx) is the correct size, shape,

position, and orientation to be the lacinia mobilis of the left man-

dible, since it closely resembles similar structures of nectiopodan

mandibles (see Schram et al. 1986). Unfortunately, recent oxidation

has made this feature nearly impossible to see. and it soon may

disappear completely. The right maxillule (RMxl) is poorly pre-

served with only the region of primary flexure visible (Fig. 6B).

The proximal section of the maxillule appears to be cylindrical,

with a blunt ridge on the dorsal surface. The distal section (Fig. 4B,

RMxl. 5) begins as a similar ridge but flares abruptly on the ventral

side. The distal elements are not preserved. The most basal part of

the limb is also missing, but under high magnification there is a

faint suggestion of short, stout setae beginning at the flexure and

extending along the ventral edge of the limb. These reach back to

the base of the maxilla in rows approximately indicated by dots on

the drawing. The presence of these setae and similar ones on the

two succeeding limbs is uncertain, since they are nearly as small as

the texture of the matrix and cannot be distinguished reliably from

artifacts of preservation or preparation.

The right maxilla (RMx2) is present on both part and counter-

part. The first segment is not well preserved, being somewhat ob-

scured by the edge of the cephalon, but appears to be fairly wide and

short (Fig. 6B). The second segment (.2) is clearly evident and is

barely longer than wide. The third and fourth segments appear fused

on the part (where the suture is not preserved) but are separate on the

counterpart (where the division is indistinct). The fourth segment

(.4) appears to be the longest one on the maxilla and is developed

dorsally as a blunt ridge. The ventral surfaces of the third and fourth

segments bear several modest spines or robust setae. Two of the

spines apparently are borne on the third segment and two on the

fourth, followed by two more stout ones at the middle of the fourth

segment. Distal to the maxilla's principal flexure, the fifth and sixth

(.6) segments are twice as long as wide, strengthened by a dorsal

ridge, and armed ventrally with many small or modest spines. Only

the proximal portion of the seventh segment (RMx2.7) is preserved,

the distal part of the limb being indicated only very faintly.

The form of the right maxilllpede (RMxp) closely resembles

that of the maxilla (Fig. 6B). The first segment is quite indistinct.

The second segment (.2) is well preserved and has both a dorsal

ridge (as do all the segments of this limb) and five ventral spines of

modest size. The third segment is long and has one or two large

spines and four modest-sized ones. The suture with the fourth

segment is distinct on the part only, with the fourth segment bent

slightly dorsad. As with the maxilla, the third and fourth segments

of the maxillipede are fused in nectiopodans. The fourth segment

(.4) is relatively short, perhaps because of distortion, and has six

small spines along the ventral edge. Distal to the principal flexure,

the ventral edge of the limb is not preserved. The fifth segment is

quite long and has a faint transverse crease near the proximal end

that appears to be diagenetic. The sixth podomere (.6) is twice as

long as wide. The seventh segment (RMxp. 7) is not preserved

distally. nor is the remainder of the limb. The maxillipede is situated

in a gap between the posterior headshield and the first tergite. The

left side of this gap appears well defined and may indicate the

presence of a vestigial tergite, though there is no other evidence to

support this possibility.

The first clearly defined tergite (Tl ) is short and no wider than

the cephalon; it apparently lacks well-developed pleura. The left

M. J. Emerson and F. R. Schram

u u

Remipede Paleontology

Figure 5. Tesnusocaris goldichi, SDSNH 28252. general view. 1 .5x.

lateral margin of this tergite appears to be serrated. Portions of the

posterior margins of the next four tergites (T2-T5) also bear faint

indications of denticulae. The second through tenth tergites (T2-

TIO) have well-developed pleura, and several have a distinct mar-

ginal ridge laterally (Fig. 7A). Although the preservation of the

tergites appears to be nearly complete, the distortion of their left

sides suggests that the dorsal surface was slightly convex in cross

section, with the pleura directed ventrolaterally. The second through

eighth tergites (T2-T8) are much wider than the headshieid. but the

ninth through twelfth (T9-T12) progressively diminish to a width

smaller than the headshield's.

The trunk limbs of Tesnusocaris are unusual and require a

special terminology. Each trunk segment bears two sets of

uniramous limbs, a condition we refer to as duplopody. We have

coined the terms "endopede" and "exopede" to emphasize the

distinct mesial and lateral positions of these limbs and their prob-

able homology with the rami of the typical crustacean limb, e.g., as

seen in the Nectiopoda (Fig. 25B). The nectiopodan trunk limb

consists of a ventrolaterally inserted protopod (often divided into a

coxa and a basis in other crustacean classes) that distally supports

both a mesial endopod and a lateral exopod. In Tesnusocaris (Fig.

26B) there appears to be ample evidence of two pairs of distinct

uniramous limbs on each trunk segment in each of the available

specimens.

The right-hand series of exopedes generally is well preserved.

These limbs are broad paddles. The first two limbs (RXl. RX2) are

very indistinct (Fig. 7A), and the second apparently overlaps the

preceding one. The third exopede (RX3) appears fragmented (Fig.

4A). The coxae (Fig. 7B) seem to be preserved at the posterolateral

comers of tergites 4 and .S (RX4. RX.^.l). whereas the coxae are

located in a slightly more anterior position on tergites 6 and 7

(RX6.I. RX7.1 ). These limbs seem to have been shifted slightly to

the right, and either exopedes 4 and 5 have been moved postenad in

relation to their tergites, or tergites 6 and 7 have been pushed

anteriad; the former condition seems more likely. Because of the

angle at which the coxae are preserved, little information can be

deduced concerning their overall structure; each appears to have a

ridge on the anterolateral surface. The exopedes associated with

tergites 8 through 10 (RX8-RX10) appear to insert more ventrally

on the body than do the preceding ones, so that only the distal three

podomeres are visible on these limbs (Fig. 8A). Since the latter

segments are the most clearly preserved examples of the entire

series, it is convenient to begin a description of the rami with the

distal segments.

The distal three podomeres of exopedes 8 through 10 are of

similar size and shape, being tlat ellipses nearly twice as long as

wide. The distal segment (.5) at least is fringed with moderately

long, stiff setae. The anterior margin of this podomere on the eighth

and eleventh limbs (RX8.5, RXl 1.5) is folded back dorsally, indi-

cating that the cuticle was thin and flexible. No setae are visible on

the more proximal segments, but their anterior edges bear marginal

flaps that appear to be folded back in some instances (Fig. 8A). The

posterior edge of each segment broadens distally into a large lobe.

This lobe on the penultimate segment of the ninth exopede (RX9)

can be seen to narrow proximally, with an articular piece filling the

resulting gap between it and the next most proximal segment. The

eleventh and twelfth exopedes (RXII, RX12) are progressively

smaller in size, and the latter is very poorly preserved, being repre-

sented by little more than a few setae at the distal tip of the limb and

at the posterolateral comer of the penultimate segment.

The total number of exopede podomeres is not clear from these

limbs, since the anterior six exopedes (RXI-RX6) are poorly pre-

served and the posterior six (RX7-RXI2) are basally obscured by

the pleura. The anterior exopede series could be interpreted as

having six or more segments, and the posterior ones as few as three.

Fortunately, there is one limb (RX 1 1 ) on specimen SDSNH 2825 la

(Fig. 10) that indicates the actual number is five. Between some of

the exopedes (e.g., RX7, RX8) the presence of isolated short seg-

ments with pointed comers apparently represents portions of the

more ventrally located endopedes, which appear to interleaf with

the exopedes to some extent. On the third through sixth tergites

(T3-T6), as well as more faintly on the others, the limbs of the two

endopedal (LN, RN) and left exopedal (LX) series can be seen

impressed through the tergites (Fig. 7C). On the fifth tergite (T5)

these appear to represent the proximal sections of the rami belong-

ing to the fourth segment (T4). In this case the limbs seem to insert

near the intersegmental junction. These limbs appear to be well

separated laterally in evenly spaced rows that have been shifted

substantially to the right, suggesting a flexible and convex ventral

surface.

SDSNH 28252 is the only specimen of Tesnusocaris in which

the terminus of the body is preserved. The division between the

twelfth tergite (T12) and anal segment (AS) is not clear, except

along the right edge (Fig. 8A). The last two segments are short, but

the preceding eleventh segment (Til) seems longer. The precise

shape of the anal segment is unclear but appears to be a tmncated

cone, somewhat rounded posteriorly on the dorsal surface. There

appear to be at least three dorsal spines of varying lengths at the

posteromesial edge of the anal tergite. though these also may be

anifacts of compression. There is also a strong lateral ridge with

modest spines (?) on the anal and twelfth segments, and this appears

to be continuous with a similar ridge on the right ventral caudal

ramus (RCV). This may be the result of diagenetic wrinkling.

Four large caudal rami extend posteriorly from the end of the

anal segment (Fig. 8B). Although all four are incomplete, it appears

that the dorsal pair (LCD, RCD) probably were somewhat longer

than the total body length, and the ventral pair (LCV, RCV) may

have been nearly equal to the body length. The bases of the rami

10

M. J. Emerson and F. R. Schram

Figure 6. Tesnusocaris goldiclii. SDSNH 28252. A, closeup of left

antennule. 8x; B. closeup of right postmandibularmouthparts. lOx.

converge and are composed of at least one (RCD.l) to three

([RCV].3) large segments. More distally. there are many faint annu-

lations that appear to divide the rami into segments approximately

twice as long as wide. Small clusters of short, faint spines on the

lateral edges of the right dorsal and ventral flagella (RCD. RCV)

suggest that they were spinose throughout their length, at least

laterally. A single spine is preserved mesially on the right ventral

ramus (LCV). As mentioned previously, these spines appear to be

associated with a lateral ridge on the proximal portion of the right

ventral ramus.

Areas composed of reddish clay (Fig. 4A, screen) lying along

the left margin of the twelfth segment (TI2) and parallel to the left

dorsal ramus (LCD) are of unknown significance.

SDSNH 28251 (Figures 9^13)

This concretion (Fig. 9) was collected in situ near the bottom of

the shale bed 5. It broke into four pieces when cracked; both pari

and counterpart were fractured along a diagonal line

separating two distinct fracture planes. The fortuitous

splitting of the concretion on two planes revealed the

preservation of at least two and probably three ani-

mals (SDSNH 28231a. b, c). The two sections of the

part and counterpart were subsequently glued together

to facilitate study. Although the overall preservation

of the fossils is poor and difficult to interpret, close

study and analysis reveal that certain structures are

remarkably well preserved and add crucial details to

our knowledge of this species. The three animals in

this concretion will be described separatelv.

SDSNH 2S25la (Figs. 10-11).— This animal is

about 60% the size of SDSNH 28252 (Table I ). which

it resembles in providing a mainly dorsal preservation

(Fig. 4). The distortion and spatial relationship of the

part and counterpart suggest that the animal was lying

on its ventral surface anteriorly, leaning slightly on the

right side, with the trunk twisting clockwise posteri-

orly to lie on its left ventral side. The anterior head-

shield lobe (Fig. 10, AHS) is large but indistinctly

preserved (Fig. 1 1 A). The left eye (LEye) is fairly well

preserved with a few facets visible around the edges in

a reddish stain (Fig. 10, screen). The lobe appears to

protrude slightly anteriad, and there are lateral exten-

sions on the posterolateral comers, giving the anterior

headshield lobe a broadly triangular outline nearly

filled by the enormous eyes. Faint suggestions of limbs

protrude from both sides on the counterpart and pre-

sumably indicate the presence of the antennules(RAI).

The remainder of the headshield is much broader

than long and subrectangular in outline; parts of the

right side are indistinct. The anterior margin protrudes

slightly between the eyes, and a definite cervical

groove is visible about midlength (Fig. 11 A). The

cervical groove divides the middle (MHS) from the

posterior headshield (PHS), though it is unclear just

where the mandibles lie relative to the groove. There

are suggestions of limb insertions at the level of both

the cervical groove (probably indicating the man-

dibles) and posterior margin of the headshield (prob-

ably the maxillipedes). The headshield exclusive of

the anterior lobe appears to be somewhat distorted.

The faintly preserved first tergite (Tl) appears to

be reduced, being short and not nearly as wide as the

headshield. Its anterior edge is obscured by the posterior margin of

the headshield, and the tergite seems to have been pushed posteriad

so that it partly overlies the anterior margin of the second tergite

(T2). The latter is indistinct but conforms well to the shape of this

tergite in SDSNH 28252 (Fig. 4. T2), with prominent pleura ex-

tending beyond the lateral edges of the headshield. The third tergite

(T3) is faintly preserved only along the left side, and the fourth (T4)

is barely visible. The remaining tergites are not preserved, but the

series of preserved limbs suggests that the full length of the trunk is

essentially complete.

The most prominent features of this specimen are the distinct

tan-colored clay clasls that appear along both sides of the trunk

(Fig. 10, screen; Fig. I IB). A careful study of the relationship of

these clasts to the few limbs that are clearly preserved and the

scarps that appear to connect them with the region of the anterior

tergites allows some conclusions regarding the significance of these

structures to be drawm. It seems that the scarps define an intercoxal

space (IcS) that occupies the ventral midline (Fig. I IB). The left

scarp appears to run along the mesial edge of the left endopedal

coxae (LN4-LNI3). A similar scarp on the right posterior region

I

Remipede Paleontology

U

Figure 7. Tesniisocciris xoldichi, SDSNH 28252, lOx. A, right anterior trunk just posterior to maxillipede with endopede pressed from below on the third

tergile: B. right side of trunk along the middle of the body showing tergites and laterally extending exopedes; C, left side of trunk with exopede and endopede

pressed from below on tergites.

appears to delineate the mesial edge of the right endopedal coxae

(RN8-RN13). which are on a slightly lower level than those on the

left, especially anteriorly. The clasts appear to be paired and lie

immediately anterior and posterior to the posteromesial comer of

the coxae. The clasts on the left side thus appear to be associated

with the left endopedal coxae (Fig. 1 IB), those on the right with the

right exopedal coxae. Since the left endopedes and right exopedes

appear to be preserved on approximately the same level, it can be

deduced that the missing left exopedes lie above the fracture plane

in the counterpart and the missing right endopedes lie below it in

the part. This, in turn, indicates a spatial separation in which the

exopedes lie more dorsal than the endopedes and presuinably insert

on the lateral angles of the ventral body wall. It is also apparent that

the left endopedes drop below the fracture plane posteriorly and

that the right exopedes and the last few right endopedes (RN12,

RN13) rise into it. revealing a clockwise twist to this specimen. The

twist and a corresponding curve to the right appear to be strongest

in the vicinity of the ninth trunk segment (LN9, RX9).

12

M. J. Emerson and F. R. Schrani

Figure 8. Tesnusocaris nohlirhi. SDSNH 2X252. 78X.4x. A, right pos-

terior trunk just anterior to the caudal rami, displaying well preserved

exopedes; B. most proximal portions of the caudal rami.

The foregoing analysis taken into account, the approximate

position of all limbs may be inferred, and consequently the identity

of those that are clearly preserved may be reasonably deduced. The

leader lines (Fig. IOC) indicate the position of the limb where

present and the presumed insertion of the coxa where the ramus is

absent (indicated in parentheses). The number of trunk segments

inferred on this specimen is thirteen, one more than observed in the

larger SDSNH 28252 (Fig. 4). The difference may be the result of

either faulty deduction on our part or individual specimen variation.

Furthermore, the preservation of the first set of limbs ( LX 1 . RX 1 )

in a position anterior to the first tergite (Tl ) is reasonable only if the

tergite has been displaced posteriorly or the limbs have been dis-

placed anteriorly during preservation. This would indicate that the

entire dorsal aspect of this specimen is probably shifted posteriad in

relation to the limbs.

Given the rather tentative identity of the few limbs that are

preserved, the following conclusions may be drawn. The coxae of

the endopedes, with the characteristic bell shape clearly preserved

on the holotype (Fig. 14). are apparent on left endopedes 10 and 12

(LNIO. LN12). the former with the proximal part of the second

podite attached. Endopedal coxae are preserved less distinctly on

right endopede L^ (RN13.1) and left endopede nine, the latter with

most of the second podite (LN9.2) attached. Although more distal

portions of several endopedal rami are preserved, the identity of the

segments cannot be specified.

Most of the exopedes on SDSNH 2885 1 A are absent or poorly

preserved. On the part, however, right exopede 1 1 (RXl 1 ) presents

the clearest view of the proximal portions of an exopede seen on

any specimen (Fig. lOA). The mesial part of the coxa is obscured by

an overlapping ramus, but the lateral side (RXl 1.1) is clearly

expressed as half of a podite resembling a broader version of the

endopedal coxa. The second segment is a short cylinder slightly

expanded at each end and probably having a dorsal ridge. The third

podite (.3) is larger and broader, with a prominent dorsal crest. On

the counterpart, this segment is largely filled by carbonized rnate-

rial, though the exact outline apparently is confused by an overiap-

ping limb. The fourth podite is less cleariy preserved but appears to

be similar in size and structure to the third. The fifth and last

segment (.5) is indicated by the lateral edge of the broad ellipse

tiiore clearly preserved on other specimens (Figs. 4. 14). The gen-

eral outline of this limb is also seen in right exopede 1 3 (RX 1 3). and

the most proximal portion is visible on right exopede 10 (RXIO). A

carbonized element resembling the third podite is assigned to left

exopede 4 (LX4.3?).

SDSNH 2S25lh (Figs. 10, 12, 13).— This specimen lies very

near the terminus of SDSNH 28251a; the two fossils are similar in

size (Table 1 ). At their closest point, the two individuals appear to

be in approximately the same plane, and it seems likely that they

were in contact at the time of burial. SDSNH 2825 lb resembles the

holotype (Fig. 14) in presenting a view of the ventral surface. The

specimen's mouthparts appear to have been exceptionally well

preserved, retaining sotne of their original shape, despite diagenelic

flattening. The head and body are slightly curved throughout their

length, especially at the juncture of the headshield and trunk, which

gives the appearance of twisting clockwise. The greater compres-

sion of the animal's left side indicates that the curling was both

lateral to the right and ventrad. with the result that the specitiien was

resting on its right dorsal surface. Considerable distortion and

apparent rupture during preservation of this individual have made

interpretation of the trunk especially difficult. The tiiost obvious

breaks have occurred ventrally between the second and third trunk

seginents and dorsally between the third and fourth tergites, with

the fonner tergite being pushed up into the fracture plane. Fortu-

nately, the cephalic region is relatively undisturbed.

The anterior headshield lobe (Fig. IOC. AHS) is faintly pre-

■served only on the part, with sections of the lateral and anterior lobe

Remipede Paleontology

13

ERRATA

Grygier, M. j

1991

margins being more defined (Fig. 1 3A). The eyes (REye, LEye) are

poorly preserved and are visible only as relatively small ellipses

impressed through the base of the anterior headshield. The anterior

region of the middle headshield (MHS) is clearly defined, and its

anterior margin protrudes slightly between the bases of the eyes on

the part. The right antennule (RAl ) extends posterolaterally. but no

detail can be seen. The left antennule is faintly preserved in a

position that indicates it has been displaced considerably to the rear

and possibly detached from its point of insertion. Details are vague,

but seem to indicate that the dorsal ramus (LAID?) is directed

posteriorly and the ventral ramus (LAIV?) extends anterolaterally,

an arrangement that would require considerable rotation from the

position indicated on the holotype (Fig. 14) and the Nectiopoda

(Fig. 25 A). The actual juncture of the rami is not clearly preserved.

The antennae may be present just posterolateral to the eyes, but

their preservation is questionable and the interpretation of this

region is not certain. They appear as faint paddle-shaped structures

(RA2?, LA2Np'?) resembling the antennal endopods of living

remipedes. with marginal setae and at least three segments. The left

antennal endopod (LA2Np?) appears to overlap distally an even

more faintly preserved structure (LA2Xp?) that resembles the large,

elliptical, setose exopod of the nectiopodan antenna. If this is the

case, and the rami were oriented in life as they are on extant

nectiopodan remipedes (Fig. 24A), then the position observed on

this fossil would seem to indicate a reversal of the relative positions

of the endopod and exopod.

The labrum (Lb) is fairly well preserved (Fig. 13B. C), but it is

not as obvious as that on the holotype (Fig. 14, Lb). The labrum is a

large subtriangular structure with a bulbous posterior lobe. The

-■■ ••"»r.'c mnnthnarts (Fig. 12) reveals some

Redescription, Ont

syn

Oph

So

Page 1, column 1, line 1- for- f^

line J. tor five read six.

square

Figure 9. Tes/iiisocaris ^nldichi, SDSNH 2825 1 , general view, 2.2x.

laterally truncated and appeals n^ ..^ .

mesial end of this structure is hidden, the size, shape, position, and

orientation are consistent with the possibility that this represents the

base of an incisor process similar to those observed in nectiopodans

(Schram et al. 1986). The right mandible also apparently is present

on the part, but is largely hidden by the overlapping maxillule

(RMx I ), from which it is difficult to distinguish separate structures.

The limbs of the posterior cephalon are remarkably well

preserved, with the luinina of many individual limb segments

lined with black carbon and the sutural septa preserved in solid

white quartzite. It seems likely that the carbon residue is associ-

ated with remnants of muscle tissue and that the quartzite indi-

cates the distribution of cuticle. The interpretation of this rich

detail is admittedly difficult, however, since the basal portions of

the limbs are on the part and the distal sections lie on the counter-