a 2
7
of Canada
Ottawa 1974
Publications
in Biological
National Museums
Oceanography, No. 7
National Museum
of Natural Sciences
Molluscs from Baffin Bay
and the Northern North Atlantic Ocean
Arthur H. Clarke
Publications
d’Océanographie
biologique, n° 7
Musées nationaux
du Canada
FESS ILEUS Re He oare Sear ye
~ CALIFORNIA
. Speen oak DE AY
| ACADEMY OF SCicIN(
, bct - 9 1974
}
LIBRARY
a Seen nce OT
Musée national
des Sciences naturelles
Molluscs from Baffin Bay
and the Northern North Atlantic Ocean
National Museum of Natural Sciences
Publications in Biological
Oceanography, No. 7
Published by the
National Museums of Canada
Staff editor
Bonnie Livingstone
Musée national des Sciences naturelles
Publications d’Océanographie
biologique, n° 7
Publié par les
Musées nationaux du Canada
Molluscs from Baffin Bay
and the Northern North Atlantic Ocean
Arthur H. Clarke
©Crown copyrights reserved
National Museum of Natural Sciences
National Museums of Canada
Ottawa, Canada
Third quarter 1974
Catalogue No. NM95-7/7
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Contents
List of Figures, vi
List of Tables, vii
Résumé, viii
Summary, ix
Biographical Note, x
Acknowledgements, xi
Introduction, 1 |
Materials and Methods, 1
Taxonomy, 13
Lepidopleuridae, 13
Patellidae, 13
Trochidae, 13
Trichotropidae, 13
Naticidae, 14
Pyramidellidae, 14
Malletiidae, 16
Limidae, 16
Verticordiidae, 18
Range Extensions, 19
Zoogeography, 21
Discussion, 22
References Cited, 23
vi
List of Figures
4
Stenosemus albus (L), Sta. 16, 13
2-4
Torellia vestita Jeffreys, Sta. 775, 13, 14
5
Melanella orphanensis (n. sp.), holotype, Sta. 6, 15
6
Pyramidella sp., Sta. 6, 15
7,8
Tindaria sp., Sta. 23, 16
9
Limatula louiseae (n. sp.), holotype, Sta. 9, 17
10, 11
Lyonsiella sp., Sta. 1039, 18
List of Maps
1
Research area, showing dredging stations, xii
List of Tables.
1
Basic station data, 2
2
Sediment data, 4
3
Mollusc species and stations, observed depths, and observed
regional distributions, 5
4
Species representation of geographic faunal groups of marine
prosobranchs and lamellibranchs, 21
Vii
viii
Résumé
En 1961, 1970 et 1971, ona fait 48 péches, principalement dans des
milieux archibenthiques et abyssaux de la baie de Baffin et de
Atlantique nord entre Terre-Neuve et I’lslande. Les prises comp-
tent 174 especes de mollusques dont plusieurs sont nouvelles et
certaines autres rarement collectionnées. L’analyse des spécimens
réevele des extensions de répartitions importantes et certaines
caractéristiques des populations:
1 on observe entre le Groenland et I’lslande une frontiére fauni-
que euro-americaine septentrionale;
2 les faunes archibenthiques et abyssales de la baie de Baffin se
différencient de celles de la mer du Labrador de maniére a
s’accorder avec |l’age géenéralement attribué a la baie de Baffin;
3 la zoogéographie des mollusques abyssaux et archibenthiques
de |’Atlantique nord parait dynamique et non pas statique. L’auteur
expose la taxonomie et la zoogéographie de plusieurs espeéces.
ll en décrit deux considérées nouvelles, la Melane/la orphanen-
sis et la Limatula louiseae.
Summary
Forty-eight hauls, principally from archibenthal and abyssal depths,
were taken in Baffin Bay and in the North Atlantic between
Newfoundland and Iceland in 1961, 1970 and 1971. The collections
contain 174 species of molluscs, including several that represent
new species, rarely collected species, or substantial range
extensions. Analysis of the material indicates that:
1 a North American—European faunal boundary exists between
Greenland and Iceland;
2 the archibenthal and abyssal fauna of Baffin Bay have differen-
tiated from the Labrador Sea fauna to an extent that is in agree-
ment with the presumed age of Baffin Bay; and
3 the zoogeography of North Atlantic archibenthal and abyssal
molluscs appears to be dynamic and not static. The taxonomy
and zoogeography of several species is discussed. Melanella
orphanensis and Limatula louiseae are described as new.
Biographical Note
Arthur H. Clarke, Head of the Invertebrate Zoology Section and
Curator of Molluscs at the National Museum of Natural Sciences,
National Museums of Canada, was born in 1926 in Danvers,
Massachusetts. He received his M.Sc. from Cornell University in
1958 for work on freshwater molluscs and his Ph.D. from Harvard
University in 1960 for research on deep-sea marine molluscs. From
1957 to 1959, Dr. Clarke worked as a marine biologist for
Columbia University, and in 1959 he joined the staff of the National
Museums of Canada. He has published approximately 80 scientific
papers, dealing principally with the taxonomy, distribution, and
ecology of North American marine and freshwater molluscs.
Dr. Clarke is past-president (1968-69) of the American Malacol-
ogical Union and is currently editor of AMU publications. He is
also associate editor of the scientific journals Malacologia and
The Nautilus. In 1971 he was appointed Adjunct Professor of
Biology at Carleton University. His current projects include
research on the molluscs of Canada and training Canadian
students in malacology and related fields.
Acknowledgements
The author is grateful to the Bedford Institute of Oceanography,
Dartmouth, Nova Scotia, for ship time and use of facilities aboard
C.S.S. Dawson and C.S.S. Hudson, to the United States Naval
Oceanographic Office, Washington, D.C., for similar support aboard
U.S.S. Lynch, and to the Museum of Natural History, Smithsonian
Institution, for access to their complete and well-managed collec-
tion of molluscs. Mr. G. Leonard Johnson, Chief Scientist on board
U.S.S. Lynch, and to the Museum of Natural History, Smithsonian
material for this study. | also thank Mr. Brian T. Kidd for excellent
and extensive assistance in the field; Mrs. Muriel F. |. Smith,
Mrs. Jane Topping and Miss Patricia Solowan for dedicated
assistance in the laboratory; and Mr. Stanley W. Gorham for
collection of material off the Grand Banks. Outstanding artistic
support was provided by Miss Aleta Karstad, who prepared the
fine specimen drawings, and Mr. Charles Douglas, who prepared
the map. Discussions with colleagues, particularly Dr. Robert C.
Bullock, Dr. Edward L. Bousfield, Dr. Roy D. Hyndman, Dr. Charlotte
E. Keen, Dr. Michael Rex and Dr. David |. Ross, were also useful.
Any errors, of course, are mine alone.
4]
Introduction
Several opportunities have arisen during the
past few years to carry out archibenthal and
abyssal dredging in Baffin Bay and the
northwestern North Atlantic Ocean. The prin-
cipal area of interest was the deep basin of
Baffin Bay, a region that contains a poorly
known and partly endemic fauna. It was
hoped that further study of the fauna might
contribute not only to a fuller understanding
of its composition and probable origin, but
also provide information of significance to
the history of plate tectonics in the region.
Of course, comparative data from adjacent
regions were necessary, and therefore
dredgings were carried out in the Labrador
and Greenland seas; previously collected
material was also studied.
The molluscan fauna collected is of un-
usual interest. A total of 174 species was
found, and several represent new species,
rarely collected species, or substantial range
extensions. Analysis of the results shows
that the species occurrences may contribute
not only to the history of geological events in
Baffin Bay, but also to a fuller understanding
of the boundaries of major zoogeographic
regions in the northern North Atlantic Ocean.
The discovery of some well-known species
far beyond their previously known geo-
graphic limits also provides evidence that
geographical distributions of some archi-
benthal molluscs may change significantly in
a few decades. This casts doubt on the
present accuracy of composite distribution
patterns deduced from museum collections
that have been assembled throughout the
past 100 years.
These questions and others are consid-
ered in some detail in the following sections.
A preliminary discussion has also been
published recently (Clarke 1973).
Map 1
Research area, showing dredging stations.
@ C.S.S. Dawson and C.S.S. Hudson stations
A U.S.S. Lynch stations
a A. T. Cameron station
Materials and Methods
Most of the specimens were collected during
three separate cruises in 1970 and 1971.
From 7 to 22 September 1970, Mr. Brian Kidd
and | travelled in Baffin Bay on board C.S.S.
Dawson, an oceanographic ship operated by
the Bedford Institute of Oceanography, Dart-
mouth, Nova Scotia. Seven dredge hauls
were taken using a modified Menzies Dredge.
Between 23 May and 4 June 1971, Mr. Kidd
was on board U.S.S. Lynch between Argen-
tia, Newfoundland, and Reykjavik, Iceland.
The U.S.S. Lynch is an oceanographic vessel
operated by the United States Naval Ocean-
ographic Office, Washington, D.C. Nine
dredge hauls were made using an Arctic
Dredge (Clarke 1972), or a standard rock
dredge modified by insertion of a wire-mesh
screen liner. After the Lynch left Iceland to
return to Newfoundland, dredging was con-
tinued by Scientist-in-Charge G. Leonard
Johnson. The modified rock dredge was
used, and an additional 26 dredge hauls
were made.
From 17 September to 10 October 1971,
| carried out another series of dredgings in
Baffin Bay, this time aboard the Bedford
Institute’s famous oceanographic vessel
C.S.S. Hudson. The Arctic Dredge was used,
and twelve archibenthal and abyssal dredge
hauls were taken with it. Five shallow dredge
hauls were also made near Thule and Godt-
haab, Greenland, using a modified Agassiz
Dredge, and shore collecting was also done
at Thule.
| also studied material collected on pre-
vious expeditions. One dredge haul in 775
fathoms near the Grand Banks of Newfound-
land is of special interest. That haul was
made by Mr. Stanley W. Gorham in 1961
from the A.T. Cameron, a Fisheries Research
Board of Canada vessel, using a modified
Agassiz Dredge. The original station number
(15%) has been changed to 775 in the table
station data and elsewhere. Specimens col-
lected by Dr. Howard Hume of Dalhousie
University, Nova Scotia, during core sam-
pling for sediment studies in Baffin Bay were
also useful. These collections and others are
referred to in the text.
Station data are summarized in Tables 1
and 2, and the mollusc species collected are
listed in Table 3.
Materials and Methods
Table 1
Basic station data
Sta.
No.
775
Lat. N.
5) Ops Papks
Serta.
51°06:6’
63°04.7’
63°06.7’
64°37.7’
64°27.8’
63°38.6’
63°17.6’
63°56.8’
62°30.5’
61°36.6’
61°22.6’
59 57-8"
60°03.7’
60°04.6’
60°04.8’
60°01 .9’
60°07.1’
60°08.6’
60°04.6’
90 30.0
oe 20
45°30’
73°19.4’
73-00.7’
73° 13.4’
73°30.24’
T3295
COTS
66°10.5’
76°34’
76°34’
76°34’
76°34’
76°34’
76°00.8’
Tf Ver’
To 90.0
74°06.4’
73° 25.8’
74°13’
7215’
71°56.8’
Long. W.
46°22.0’
oo 09.0
37°47.3’
24°02.8’
24°00.0’
23°58.3’
24°23.1/
23°24.4’
24°13.5’
26°51.4’
2f 22.0
23-20,1
28°43.9’
46°35.4’
46°49.5’
46°50.6’
46°44.0’
46°41.1’
47°01.7’
47°06.5’
47°10.5’
42°54.2’
51°42.2’
48°17’
13, 02.5’
74°34.’
Gf St.d
65°33.24’
64°33.9’
Sr oT es
57°33.6’
68°50’
68°50’
68°50’
68°50’
68°50’
tt to
75°31.4’
74°17.4’
T1278
66°55.3’
62°09’
63°47’
62°46.8’
Depth (fm)
Region (uncorrected)
U.S.S. Lynch, 1971
Labrador Sea 958
Labrador Sea 2354
Labrador Sea 1918
Iceland Shelf 240
Iceland Shelf 220
Iceland Shelf 58
Iceland Shelf 86
Iceland Shelf oF
Iceland Shelf 55
Iceland Shelf 320
Greenland Sea 650
Greenland Sea 600-700
Greenland Sea 620-740
Greenland Shelf 260-320
Greenland Shelf 800-950
Greenland Shelf 660-700
Greenland Shelf 550-650
Greenland Shelf 380-460
Greenland Shelf 405-490
Greenland Shelf 220-400
Greenland Shelf 480-650
Labrador Sea 1810
Labrador Sea 215
A.T. Cameron, 1961
off Grand Banks 775
C.S.S. Dawson, 1970
Baffin Bay 509
Baffin Bay 489
Baffin Bay 1220
Baffin Bay 1268
Baffin Bay 1027
Baffin Bay 447
Davis Strait 314
C.S.S. Hudson, 1971
Thule beach
Thule 92
Thule 25
Thule 85-115
Thule 95-110
Baffin Bay 260
Baffin Bay 312
Baffin Bay 208
Baffin Bay 600
Baffin Bay 1280
Baffin Bay 360
Baffin Bay 1237
Baffin Bay 1202
Gear
DAVIDOV I AI VV SS SS
op)
3552255
PPrrrrrrrnnnn
Date
May
May
May
June
June
June
June
June
June
June
June
June
June
June
June
June
June
June
June
June
June
June
June
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Oct.
17
Materials and Methods
Sta. Depth (fm)
No. Lat. N. Long. W. Region (uncorrected) Gear! Date
1065 72°08.8’ 61°38.0’ Baffin Bay 1000 A oS.
1066 70°31.0’ 63° 16.3’ Baffin Bay 1150 A Oct. 2
to to
70°31.4’ 63°17.3"
1067 68°28.3’ 61°59.6’ Baffin Bay 975 A Oct. 4
to to
68°29.1’ 62°02.8’
1068 65°46.5’ Sf°52.¢ Davis Strait 295 A Ot.” F
1069 64°10’ 51°43.3’ Godthaab 30 S Oct. 10
1. A Arctic Dredge R_ rock dredge
M Menzies Dredge S small biological dredge (Agassiz Dredge)
Materials and Methods
Table 2
Sediment data
Particle size distribution: per cent within size classes (mm) ae
particle
1.0- 0.5—- 0.25- 0.12— 0.063- 0.032— 0.016- 0.008- 0.004- <.002 | size
0.12 0.063 0.032 0.016 0.008 0.004 0.002 classes
silt, clay
silt, clay
silt, clay
silt, sand
Clay, silt
Clay, silt
Clay, silt
sand
Clay, silt
silt, sand
silt, clay
Clay, silt
Clay, silt
Clay, silt
Clay, silt
Clay, silt
Clay, silt
Clay, silt
silt, clay
Materials and Methods
Table 3
Mollusc species and stations, observed depths, and observed regional distributions’
Species
Polyplacophora
Lepidopleuridae
1. Lepidopleurus alveolus (M. Sars)
2. Lepidopleurus asellus (Spengler)
3. Stenosemus albus (L)
4. Hanleya hanleyi (Bean)
Aplacophora
5. Proneomenia sp.
6. Chaetoderma cf. nitidulum Lovén
7. Chaetoderma sp.
Gastropoda
Fissurellidae
8. Emarginula fissura (L)
9. Puncturella noachina (L)
Patellidae
10. Lepeta caeca (Miller)
11. Pilidium fulvum (Miller)
Trochidae
12. Margarites costalis (Gould)
13. Margarites groenlandicus
(Gmelin)
14. Margarites olivaceus (Brown)
15. Margarites umbilicalis
(Brod. & Sby.)
16. Margarites vahli (M@ller)
17. Lischkeia ottoi (Philippi)
18. Solariella obscura (Couthouy)
19. Solariella varicosa (Migh. & Ad.)
20. Calliostoma occidentale
(Migh. & Ad.)
Seguenziidae
21. Seguenzia reticulata (Philippi)
Rissoidae
22. Cingula arenaria (Migh. & Ad.)
23. Alvania janmayeni (Friele)
24. Alvania scrobiculata (Muller)
25. Cithna tenella (Jeffreys)
Stations
6
14
16
14, 29, 36
1034
1033, 1034
1033, 1058
(17)
(6), (14), (23),
(32), (35), (37),
(1039), 1069
1054, (1058),
(1069)
(32)
1054
1069
1054
1054
(35), (37), 1033,
1034, 1039
775
(37)
40
36
(23)
1039
1033, 1034, 1039
(1039), (1058)
7
Minimum
Depth-range
220-(260)
489
489-509
312-509
(37)
30-(220)—
(958)
25-(30)-
(312)
(550)
314-509
775
(480)
215
220
(600)
314
314-509
(312)-(314)
2354
Off Grand Banks
Labrador Sea
(t)
Off S. Greenland
(t)
Baffin Bay
(t)
Off S. W. Iceland
—+—+—+ |
on
Materials and Methods
Species
Cerithiopsidae
26. Cerithiopsis costulata (Mller)
27. Cerithiella metula (Lovén)
28. Laeocochlis granosa (Wood)
Aporrhaidae
29. Aporrhais occidentalis (Beck)
30. Aporrhais serresiana (Michaud)
Trichotropidae
31. Torellia vestita Jeffreys
32. Trichotropis borealis
Brod. & Sby.
Naticidae
33. Amauropsis islandica (Gmelin)
34. Polinices pallida (Brod. & Sby.)
35. Natica clausa Brod. & Sby.
Epitoniidae
36. Acirsa costulata (Migh. & Ad.)
37. Epitonium obtusicostatum
(G. O. Sars)
Aclididae
38. Aclis walleri Jeffreys
Eulimidae
39. Eulima stenostoma Jeffreys
Muricidae
40. Boreotrophon clathratus (L)
41. Boreotrophon fabricii (Beck)
42. Boreotrophon truncatus (Str@m)
Columbellidae
43. Pyrene costulata (Cantraine)
Buccinidae
44. Beringius ossiani (Friele)
45. Volutopsius norvegicus (Gmelin)
46. Colus glaber (Verkruzen)
47. Colus fusiformis (Thorson)
48. Colus krampi (Thorson)
Stations
(1039)
6, (13), (14), (32),
1039
(29), (35), (775),
1039, (1068)
(1039)
(14)
775
(14), (1039)
16
(14)
(13), (14), 15,
(21), (30), (35),
(775), 1058,
1059, 1062
(6), (13)
(23), (32), (33),
(35)
(26)
(13), (14)
(13), (327), (37?)
(147), (1039),
(1069)
(13), (147?)
(23)
(32)
(21), (23), (29)
(21)
16
1036, 1039, 1061,
1065
Minimum
Depth-range
=)
(314)
314-958
(295)-314—
(775)
(314)
(220)
775
(220)-(314)
86
(220)
58-360-
(800)
(240)-(958)
(460)-(600)
(620)
(220)-(240)
(240)-(4807)
(30)-(314)
(220?)—(240)
(600)
(550)
(320)-(600)
(320)
86
314-1280
Off Grand Banks
Labrador Sea
(t)
Off S. Greenland
Baffin Bay
es Ge
Off S. W. Iceland
Materials and Methods
Species
49. Colus latericeus (Moller)
50. Colus tortuosus (Reeve)
51. Colus turgidulus minor (Thorson)
52. Colus ventricosus (Gray)
53. Plicifusus kroyeri (Moller)
54. Neptunea despecta (L)
55. Neptunea satura (Martyn)
56. Buccinum cyaneum Bruguiére
57. Buccinum eilatior Tryon
Stations
(32), (775)
1058, (1064),
(1065)
14), (22), (29),
(31), (35)
(1054)
(= B. tenue Gray, preocc.; see Baily 1961)
58. Buccinum finmarkianum
Verkruzen
59. Buccinum hydrophanum
Hancock
60. Buccinum sericatum Hancock
Nassariidae
61. Nassarius incrassatus (Strom)
Cancellariidae
62. Admete couthouyi (Jay)
Turridae
63. Spirotropis carinata (Philippi)
64. Oenopota cinerea (Moller)
65. Oenopota declivis (Lovén)
66. Oenopota cf. decussata
(Couthouy)
67. Oenopota cf. incisula (Verrill)
68. Oenopota nobilis (Moller)
69. Oenopota cf. pyramidalis
(Strom)
70. Oenopota reticulata (Brown)
71. Typhlomangelia nivalis (Lovén)
Pyramidellidae
72. Eulimella compactilis Jeffreys
73. Melanella orphanensis (n. sp.)
74. Pyramidella sp.
Scaphandridae
75. Cylichna alba (Brown)
76. Cylichna cylindracea Pennant
(1039), 1057
1053, 1054, 1055,
1058, 1059
(36)
hW;20
(13), (14), (40),
1058
(13), (14)
1039
(13), (14),1033,
(1034), 1039,
1057, 1068
(6), 14, 1034
(40), 1057, 1058,
1059
(14)
1039, 1068
(6)
(6)
(6), (35), (40),
1039, (1056)
1033, 1034, 1035,
1036, 1056, 1058,
1060, 1068
Minimum
Depth-range
fm
(650)-775
312-(1202)
(490)-(550)
(775)
(260)
(220)-(660)
260-(314)
25-312
(220)
37-55
(240)-312
(220)-(240)
314
(220)-260-
509
220-489-
(958)
260
220
(220)
208-312
(220)
295-314
(958)
(958)
(100)-314-
(958)
100-1268
Off Grand Banks
Labrador Sea
(t)
Off S. Greenland
(t)
Baffin Bay
Off S. W. Iceland
Materials and Methods
” a | To
aoe ae c
) a. @- = ro
e se) ce © > <=
” Eos = 5 = (40) :
. -— = © s = .
Species = =a me 5 . = ¥
a) Pe | oO a oO aa) e)
fm
77. Cylichna propinqua M. Sars 1033, (1057), (260)-509 ~ ~ - t ~
(1068)
78. Scaphander nobilis Verrill (775) (775) (t) - - - -
79. Scaphander punctostriatus (6) (958) - (ft) - - as
(Migh. & Ad.)
Philinidae
80. Philene quadrata Wood 6 958 - Tt ~ ~ ~
Diaphanidae
81. Diaphana globosa Lovén (6) (958) - (ft) - - ~
82. Diaphana hiemalis Gould 1068 295 - ~ - t -
Aeolidiidae
83. Aeolidia sp. 17 37 - - ~ - t
Scaphopoda
Siphonodentaliidae
84. Siphonodentalium lobatum 1033, 1034, 295-509- - - - t ~
(Sowerby) (1060), 1062, (600)
1068
Dentaliidae
85. Dentalium agile M. Sars (23) (600) ~ - ~ - (ft)
86. Dentalium entale L 13, 14, 15, 16, 21 58-320 - - - - t
87. Dentalium occidentale (14), 1039, 1068 (220)—-295- - - _ H) (t)
Stimpson 314
Pelecypoda
Nuculidae
88. Nucula atacellana Schenck 6 958 - Tt - - -
(= N. cancellata Jeffreys, non Meek)
89. Nucula belloti Adams 1058 312 - - - t -
90. Nucula delphinodonta 1033, 1034, 1038, 208-509 - ~ - 5 -
Migh. & Ad. 1039, 1057, 1059,
1068
91. Nucula proxima Say 40 215 - T - - -
92. Nucula tumidula Malm 13, 14 220-240 ~ - ~ - Tt
Malletiidae
93. Tindaria sp. (23) (600) - - - - @
Nuculanidae
94. Pristiglioma nitens (Jeffreys) 73 1918-2354 - - _ =
95. Ledella confinis (Smith) (6), (7) (958)—(2354) - - - -
96. Ledella messanensis (Seguenza) 6, 23 700-958 - is ate t
97. Nuculana minuta (Miller) (16), 1053, 1054, 25-95 = = T+ ae
1056
98. Nuculana pernula pernula (775) (775) 7). => - - -
(Muller)
Materials and Methods
Species
99. Nuculana pernula costigera
(Leche)
100. Nuculana sp. (juv.)
101. Yoldiella expansa (Jeffreys)
102. Yoldiella intermedia (M. Sars)
103. Yo/diella iris Verrill & Bush
104. Yoldiella lenticula (Moller)
105. Yoldiella lucida (Lovén)
106. Yo/diella sp. (juv.)
107. Megayoldia thraciaeformis
(Storer)
Arcidae
108. Bathyarca glacialis (Gray)
109. Bathyarca “pectunculoides”
(Scacchi)
110. Bathyarca profundicola Verrill
111. Arca nodulosa Muller
Limopsidae
112. Limopsis cristata Jeffreys
113. Limopsis minuta Philippi
Mytilidae
114. Dacrydium vitreum (Mller)
115. Modiolus phaseolinus (Philippi)
116. Musculus discors laevigata
(Gray)
117. Musculus nigra (Gray)
Pectinidae
118. Cyclopecten abyssorum
(Lovén)
119. Cyclopecten groenlandicum
(Sowerby)
120. Cyclopecten imbriferum
(Lovén)
121. Cyclopecten vitreum (Gmelin)
122. Chlamys furtiva (Lovén)
123. Chlamys islandicus (Muller)
124. Chlamys septemradiatus
(Muller)
Stations
1056, (1059)
(40)
(1034)
(40), 1033, 1034,
1039, 1057, 1058,
1059, 1060, 1062
(23)
1057, 1058,
(1059)
40, 1033, 1034,
1039, 1054, 1057,
1062, 1068
(13), 14, (23),
(26), (32), (35),
(37), 1035, 1036,
1061, 1064
9
21, 36
(13), (14)
6, 13, (23), (26),
(32), (35), 775
6, 1039, 1057,
1058, 1062
16, 17, 20
1053, 1054, 1056,
1069
1056
1039
(13), (14), 1034,
1038, 1062
(23), (26), (35),
1062, (1038),
(1068)
775
(14)
(29), (36), (1054),
(1069)
(13), (14), (21),
(23), (29)
Minimum
Depth-range
fm
100-(208)
(215)
(489)
208-600
489
360
220-958
(600)
(208)—260-
312
25-509
220-1280
1918
320
(220)-(240)
240-958
260-958
37-86
25-95
95
314
(220)-360-
489
(295)-360-
(620)
775
(220)
(25)—(260)
(220)—(600)
Off Grand Banks
Labrador Sea
(t)
Off S. Greenland
(t)
Baffin Bay
Off S. W. Iceland
Materials and Methods
” TD T
Sas £2 E
® faa) oO (= ®
1©)) io) oO Ss)
= = be es © a
c te © 7" Oo aa =
Species = E = 6 2S « “fa
S Eo = Lg SS Sa
a =a oS 6% a3
fm
125. Chlamys striatus (Miller) (20) (55) - ~ ~ - (ft)
126. Hinnites distorta (da Costa) 17, (20) 37-(55) - _ = = +
Limidae
127. Limatula elliptica Jeffreys (35) (405) - vi af): ailbes =
128. Limatula hyperborea (Jensen) 6, 13, (23);-1039, 240-958 - 03 _ t t
1068
129. Limatula subauriculata 14 220 ~ - - - +t
(Montagu)
130. Limatula louiseae (n. sp.) 9 1918 - G) ~ - -
131. Lima (Acesta) excavata (23), (31) (680) - -— (t) - (t)
(Fabricius)
Anomiidae
132. Monia patelliformis (L) 17, (20) 37—(55) ~ - ~ - +
133. Anomia aculeata Muller 29 260 ~ - t - -
134. Anomia ephippium L 16 86 - - - - 3
Astartidae
135. Astarte borealis (Schumacher) 1054, 1056, 1057, 25-312 - ~ - + -
(1058), 1059
136. Astarte crenata Gray 13, (16), (20), 21; (30)—240- - ~ t | (t)
29, (32), (35), 489-(1210)
(37), 1034, 1039,
1057, (1059),
(1061), 1068,
(1069)
137. Astarte elliptica Brown (1069) (30) - - (t) - ~
138. Astarte montagui (Dillwyn) 1054, 1057, 1059 25-260 - - - t ~
139. Astarte subaequilatera 13, 14 220-240 ~ - - - tT
(Sowerby)
Thyasiridae
140. Thyasira equalis(Verrill&Bush) 1033, 1034, 1036, 209-1268 - - ~ t -
1059, (1060)
141. Thyasira gouldi Philippi 40, 1039, 1057, 208-314 ~ tT = t ii
1058, 1059
142. Axinulus eumyarius (M. Sars) 6 958 - f pee
143. Axinulus ferruginea 13, 14 220-240 - ~ - - }
Winckworth
144. Axinulus pygmaeus 1033, 1034 489-509 - - - 4) ~_
(Verrill & Bush)
145. Axinulus succisa Jeffreys 6 958 - t a OR gD? a
146. Axinopsis orbiculata G.O. Sars —_ (13), 1059 208-(240) - - = t2on-Ghi
Erycinidae
147. Kellia suborbicularis(Montagu) 17 37 > Woe) |) saloon
Cardiidae
148. Serripes groenlandicus (35), (1054) (25)-—(405) =~ = i “ae
(Gmelin)
10
Materials and Methods
Species
149. Clinocardium ciliatum
(Fabricius)
150. Parvicardium ovale (Sowerby)
151. Parvicardium scabrum
(Philippi)
152. Cerastoderma elegantulum
(Beck)
Veneridae
153. Venus casina L
154. Venus (Timoclea) ovata
Pennant
Mactridae
155. Spissula elliptica (Brown)
Psammobiidae
156. Gari fervensis (Gmelin)
157. Gari (Psammobella) tellinella
(Lamark)
Semelidae
158. Abra nitida (Muller)
Tellinidae
159. Macoma calcarea (Gmelin)
160. Macoma loveni (Jensen)
161. Macoma moesta (Deshayes)
Hiatellidae
162. Hiatella arctica (L)
Myidae
163. Mya truncata (L)
Thraciidae
164. Thracia myopsis ‘‘Beck”
Moller
Laternulidae
165. Periploma abyssorum Verrill
Verticordiidae
166. Lyonsiella abyssicola M. Sars
167. Lyonsiella sp.
Stations
(1054)
(16), (20)
13, 14, (16)
1054
20
14, 20
16, 17
15
16, 20
14
1053, (1054),
1055, 1056,
(1069)
1056, (1059)
1053, 1054,
(1055), 1056
16, 17 (1052),
1053, 1054,
(1055), 1056,
1069
(1052), 1054,
(1069)
1059
1059
1033
1039
Minimum
Depth-range
fm
(405)
(55)—(86)
(86)—220-
240
25
55
55-220
37-86
58
55-86
220
(25)-92-95
95-—(208)
25-95
30-95
(0)—25-(30)
208
208
509
314
Off Grand Banks
Labrador Sea
Off S. Greenland
(t)
(t)
Baffin Bay
Off S. W. Iceland
(t)
t
—+ +
11
Materials and Methods
g Z Z
= o oc
w Se = =
f<d) faa oO = ®
D ” o an
a = = a = w é
c 5s > S = O fea) =
Species 2 E< 5 £¢ 6 £ae
S = a a
” =O O a O co Oo
fm
168. Verticordia sp. 1069 30 - - " ~ -
Poromyidae
169. Cetoconcha nitida (Verrill) 775 775 t ~ - - -
Cuspidariidae
170. Cuspidaria exigua Jeffreys 23(?), 1034, 360-1000 eee Ch) (2)
1062, 1065
171. Cuspidaria glacialis G. O. Sars 26, 40(?), 1033 215(?)- - (?) - (iene
(509)-(620)
172. Cuspidaria lamellosa (M. Sars) 1039, 1068 295-314 - - ~ ~
173. Cuspidaria pellucida 1034, 1062 360-489 ~ - - -
Stimpson
174. Cuspidaria subtorta (G.O. Sars) 1057, 1059 (208)-260 - - =. Giaare
1. Numbers and symbols without parentheses — indicates absence or failure to detect presence;
fap FeSghe ivune SPeCHeRns: Symbols within circles indicate new _ regional
Numbers and symbols within parentheses _ records;
represent empty shells; ? indicates uncertain identification (usually juve-
t indicates presence; nile specimens).
12
Taxonomy
Most of the species collected during this
survey have been discussed and illustrated
in the relevant literature, for example, Sars
1878; Thorson 1941, 1944, 1951; Madsen
1949; Ockelmann 1958; Tebble 1966; Mac-
pherson 1971; Lubinsky 1972. It is therefore
unnecessary to discuss them all here. How-
ever, some of the species appear to be new,
and others exhibit unusual morphological
features or contribute to the solution of tax-
onomic problems. The following remarks
pertain to such species.
Lepidopleuridae
Smith (1960) has shown that Stenosemus
Middendorff, 1847, is-an available generic
name, with Chiton albus Linnaeus as its
type species. Lophyrochiton Yakovleva, 1952
(type, C. a/bus L.), is therefore an objective
synonym, and the species called Lophy-
rochiton albus by recent authors is here
cited as Stenosemus albus. The specimens
of S. albus reported here were taken off
southwestern Iceland in 86 fathoms and they
show unusual variation. The four specimens
form a series progressing from almost pure
white with some brown mottling on the pos-
terior valves to heavy chestnut with rust-red
mottling on all valves (Figure 1).
Patellidae
The single specimen of Pilidium fulvum is an
empty shell but with adherent periostracum.
It is of the rare white “variety”’.
Trochidae
The Solariella obscura is an empty, half-
grown specimen but is referable to ‘‘variety”’
bella Verkrizen as illustrated by Odhner
1912.
Trichotropidae
Six specimens of Torellia were collected
alive off the Grand Banks in 775 fathoms.
They are exceedingly variable in regard to
periostracal “hair”, but the extreme speci-
mens are connected by intergrades (Figures
2, 3, and 4). One extreme is evenly covered
with short, fine hair. This is much like the
figures in Jeffreys (1867, Pl. 4, fig. 1) and
Sars (1878, Pl. 22, figs. 1a, 1b) of Torellia
vestita Jeffreys except that the spire is some-
what lower, as noted by Verrill (1882:521).
The other extreme is densely covered with
long, flat hairs arranged in ten spiral rows on
the body whorl. This is undoubtedly the
T. fimbriata of Verrill and Smith (Verrill
1882:520, Pl. 57, fig. 27). Some of the inter-
mediate specimens also match Verrill’s de-
scription of Torellia fimbriata var. tiarella
(Verrill 1882:521). It is quite apparent that
only one species is represented in our
material, and the relatively smooth specimen
is so much like the descriptions and figures
of 7. vestita that it undoubtedly is that
species. Therefore, both T. fimbriata Verrill
and Smith and var. tiare//a Verrill must be
regarded as synonyms of T. vestita Jeffreys
at the species level. Whether or not a dis-
Figure 1
Stenosemus albus (L), Sta. 16
Figure 2
Torellia vestita Jeffreys, Sta. 775
13
Taxonomy
yy
RV atiest
ers
wet
Figure 3
Torellia vestita Jeffreys, Sta. 775
crete North American subspecies exists must
remain unknown until much more material
can be acquired and studied.
Naticidae
The Natica clausa from Station 15 is unusual
in that it is reddish-brown, with a distinct
white band below the suture and white on
the base. See Odhner 1913:14 for an exten-
sive description of variation in N. clausa.
14
1mm |
Figure 4
Torellia vestita Jeffreys, Sta. 775
Pyramidellidae
Melanella orphanensis, n. sp.
Figure 5
Description
Shell small (about 1/6 inch), turriculate,
white, slightly bent, and with narrow axial
riblets irregularly spaced on the early whorls.
About nine whorls on holotype. Nuclear
whorl deviated paucispiral. Early postnuclear
whorls plano-convex, with a_ translucent
band below the suture, a transparent band
above the sutures, and with close but irreg-
ularly spaced white axial thickenings be-
tween the suprasutural and subsutural bands.
Late postnuclear whorls predominantly flat
but noticeably convex above sutures and
with axial thickenings fewer but extending to
both sutures. Sutures impressed. Body whorl
with a poorly defined, low, subangular spiral
peripheral band and a similar spiral band
below it intersecting the top of the aperture.
Spire narrow and slightly bent. Aperture
small, prosocryt, orthocline, mostly basal,
angular above, sharply convex below; outer
lio narrow and evenly curved; inner lip
thickened and intersecting the columella
within the aperture. Umbilicus absent. No
operculum seen.
Holotype: height, 4.2 mm; width, 1.3 mm;
number of whorls, 9.
Taxonomy
Figure 5
Melanella orphanensis (n. sp.), holotype, Sta. 6
Types
Only the holotype is known and this is an
empty shell in fine condition except for a
small chip near the base of the outer lip. The
specimen was dredged in the Labrador Sea
on Orphan Knoll at Station 6 (50°32.9’/N,
46°22.0’W, 961 fm) by Mr. Brian T. Kidd on
23 May 1971. It bears catalogue number
66345 and is in the National Museum of
Natural Sciences, Ottawa.
Remarks
| cannot locate any other species that has
the bent spire and ribbed axial sculpturing of
M. orphanensis. Nothing like it has been
seen in museum collections in eastern North
America or in the literature. The bent spire is
Figure 6
Pyramidella sp., Sta. 6
characteristic of Melanella but, with the
exception of growth lines, none of the
species known to me possess axial sculptur-
ing. The axial sculpturing is quite distinctive,
and the holotype therefore appears not to be
a deformed specimen of any species that is
normally not bent. The species may deserve
separate supraspecific status but more ma-
terial should be available before that deci-
sion is made.
A single Pyramidella was also taken at
Station 6. The specimen was dead, some-
what worn, and its aperture was occupied by
a sipunculid worm tube. The mollusc appar-
ently belongs to an undescribed species but
its condition is not good enough to provide
a suitable basis for description of a new
species. The specimen, with the sipunculid
tube removed, is shown in Figure 6.
15
Taxonomy
Figure 7
Tindaria sp., Sta. 23
Malletiidae
A single valve of Tindaria was taken at Sta-
tion 23 (61°36.6’N. 28°25.7’W, 600-700 fm)
on the Reykjanes Ridge using a rock dredge.
It also appears to be an undescribed species
but is too incompiete to describe. The speci-
men is illustrated in Figures 7 and 8.
16
Figure 8
Tindaria sp., Sta. 23
Limidae
Limatula louiseae, Nn. sp.
Figure 9
Description
Shell minute (about 1/10 inch long), similar
in shape to other species of Limatula, in-
flated, thin, fragile, translucent and concen-
trically ribbed. Sculpture consists of about
30 sharp, narrow, concentric ribs, a few of
which are wider than the others and are
lamellate; poorly defined whitish, radial
streaks across the central portion of the
valves; and fine whitish lines on the anterior
and posterior slopes approximately perpen-
dicular to the hinge line and diagonally
intersecting the concentric ribs. Umbones
rounded, projecting beyond the hinge, and
with centrally worn apices apparently caused
by mutual abrasion when the valves are
opened. Auricles short and equal. Hinge
straight, with ligament pit shallow, centrally
located, V-shaped above, rounded below,
and projecting below the hinge line. Interior
whitish, with external ribs and lines clearly
visible. |
Holotype: length, 2.3 mm; width, 1.6 mm;
inflation (valves appressed), 1.6 mm.
Taxonomy
are tS areas PCE AY Pte LS SADA aS Re
to
Figure 9
Limatula louiseae (n. sp.), holotype, Sta. 9
Types
The holotype, a living specimen, was dredged
by Mr. Brian T. Kidd on board U.S.S. Lynch
at Station 9 (51°06.6’N, 37°47.3’W, 1,918 fm)
in the Labrador Sea not far from the western
foothills of the Mid-Atlantic Ridge. It is in
the Mollusc Unit, National Museum of Natural
Sciences, Ottawa, and bears catalogue num-
ber 66418. Limatula Iouiseae is named in
fond memory of the late Louise Robinson
Clarke, my good wife and dear friend, for
25 years.
Remarks
This small Limatula differs from L. elliptica
(Jeffreys), L. subauriculata (Montagu), L.
subovata (Jeffreys) and all other northern
species seen, in that its dominant sculptur-
ing is concentric and not radial. The species
cited, and other species, also exhibit con-
centric lines but none have the prominent
lamellate cords of L. /ouiseae. |t is closer to
Limatula laminifera (Smith) than to any other
Known species, but it is more equilateral and
has microscopic lines on the anterior and
posterior slopes diagonal to the lamellae, a
feature that apparently (Stuardo 1968) does
not occur in L. /aminifera. In addition, L.
laminifera is from mid-archibenthal depths in
the West Indies. Thus, on zoogeographic
grounds alone it is unlikely that the two
populations represent the same species.
Limatula louiseae was found in somewhat
deeper water than the deepest previous
record for a Limatula, that is, L. subauriculata
in 1,785 fm (Clarke 1962). It may be an im-
mature specimen but, if so, appears to be
quite different from the young stages of any
other North Atlantic species.
a7
Taxonomy
-———————
1mm
teint sent ener ernen ante meen —ereenavmernmenstsnmrrent|
1mm
Figure 10 Figure 11
Lyonsiella sp., Sta. 1039 Lyonsiella sp., Sta. 1039
Verticordiidae
Two small living specimens of Lyonsiella
were found at Station 1039 (66°10.5’N,
57°33.6’W, 314 fm) on the saddle of the Davis
Strait Sill. They do not appear to belong to
any known species, but since they are ap-
parently quite immature their identity cannot
be established with certainty. (Figures 10
and 11).
18
Range Extensions
Several of the species found represent sub-
stantial range extensions. These species
with the exception of those which have
already been discussed or have not been
confidently identified, are listed below.
Pilidium fulvum (Muller) occurred as a
fresh, empty shell off southern Greenland in
550-650 fm. The species is recorded from
Iceland and farther east (Thorson 1941) but
not from the North Atlantic west of Iceland.
Calliostoma occidentale (Mighels and
Adams) was found alive off southern Green-
land in one dredge haul taken in 220-400 fm.
it was previously known only from North
America (off Sable Island, Nova Scotia, to
off New Jersey) and Europe (northern Nor-
way to Scotland) (Clench and Turner 1960).
Cerithiella metula (Lovén) was taken alive
in Davis Strait and the Labrador Sea and as
empty shells off southern Greenland and
southwestern Iceland. The species was
known previously only from Iceland eastward
(Thorson 1941).
Laeocochlis granosa (Wood) occurred off
the Grand Banks (empty but fresh-looking),
in Davis Strait (alive and dead), and off
southern Greenland (dead but fresh). Sars
(1878) recorded it only from the Norwegian
Sea, but Thorson (1941) later recorded it
from West Greenland (alive) and Iceland
(shells). It has not been recorded previously
from off the coast of North America.
Acirsa costulata (Mighels and Adams) was
found, as empty shells, in the Labrador Sea
and off southwestern Iceland. It was pre-
viously known only from West Greenland and
the coast of North America south to Massa-
chusetts (Clench and Turner 1950).
Epitonium obtusicostatum (Sars) was
taken, shells only, on the Reykjanes Ridge
southwest of Iceland and off southern
Greenland. Thorson (1941) recorded empty
shells from Iceland and Norway (no living
specimens) but not west of Iceland.
Aclis walleri Jeffreys was collected empty
from the Reykjanes Ridge off southwestern
Iceland. It is recorded from off Norway
(Thorson 1941) and from the Labrador Sea
(Thorson 1951) but not Iceland.
Neptunea satura (Martyn) was found alive
and as empty shells off southwestern Iceland.
The species is not listed from Iceland by
Thorson (1941). Golikov (1963) gives the
range of N. satura as extending from the
coast of Yukon Territory to southern Alaska
and Kamchatka and across the arctic coast
of Eurasia to Finland and Spitzbergen. The
Iceland records apparently represent the
farthest extension into the North Atlantic that
this species has so far achieved.
Eulimella compactilis Jeffreys was col-
lected alive from two localities in the central
part of Davis Strait. Thorson (1944) records
this species in the North Atlantic only near
or south of Lofoten Is., Norway.
Ledella confinis (Smith) was found, as
empty shells, at two localities in the Labra-
dor Sea in 958 and 2,354 fm. It was known
previously only from the Mid-Atlantic Ridge
and the Canaries Basin in depths of 410-
1,150 fm (Clarke 1962).
Arca nodulosa Muller occurred alive
southwest of Iceland and near Cape Fare-
well, Greenland. It has not previously been
recorded west of Iceland (Madsen 1949).
Cyclopecten abyssorum (Lovén) was found
living in 314 fm in Davis Strait. Previous
records are all from the eastern Atlantic from
the Norway Basin south to the Cape Verde
Basin (Clarke 1962).
Chlamys septemradiatus (Muller) was
found as empty shells southwest of Iceland
(including a locality on the Reykjanes Ridge)
and near Cape Farewell, Greenland. It was
recorded by Madsen (1949) only from Iceland
and eastward to the coast of Europe.
Axinulus pygmaeus (Verrill & Bush) was
found abundantly at two localities in north-
western Baffin Bay at 489 and 509 fm. It was
Known previously only from the North Ameri-
can Basin and near Iceland (Ockelmann
1958).
Cuspidaria exigua Jeffreys was found alive
in three dredge hauls from northwestern and
east-central Baffin Bay and occurred empty
(identification uncertain) southwest of Ice-
land. It has been recorded only as empty
shells from the vicinity of Jan Mayen, Spitz-
bergen, and Norway (Ockelmann 1958).
Cuspidaria pellucida Stimpson occurred
alive at two localities in northwest and
east-central Baffin Bay in 360 and 489 fm.
Ockelmann (1958) records it only from off
North America between Newfoundland and
Cape Cod.
Cuspidaria subtorta (G.O. Sars) was col-
lected alive at one locality and empty at
another, both in northern Baffin Bay. It was
previously recorded doubtfully from West
Greenland and the coast of North America
between Newfoundland and Cape Cod, and
recorded positively from East Greenland
eastward to off the coast of Europe (Ockel-
mann 1958).
19
Range Extensions
Some other species are recorded here
from localities in Baffin Bay that are signif-
icantly farther north than those previously
known. The most extreme examples are
Oenopota reticulata (Brown), previously
known (doubttfully) from near Frobisher Bay
(Macpherson 1971) and now recorded 600
miles to the north, and Megayoldia thraciae-
formis (Storer), Known previously as far
north as Upernavik, Greenland (Thorson
1951), and here recorded from localities 300
miles farther to the north.
20
Zoogeography
At first sight the molluscan fauna dredged
near Iceland appeared quite different from
those dredged in Baffin Bay and along the
coast of North America. Further examination
showed the presence of several genera and
species that do not occur in the western
Atlantic, for example, Emarginula fissura,
Aporrhais serresiana, Nassarius incrassatus,
Arca nodulosa, Modiolus phaseolinus,
Chlamys septemradiatus, Hinnites distorta,
Parvicardium spp., Venus casina, Gari spp.,
etc. Immediate questions arose, such as,
where does the transition zone occur be-
tween the European and North American
fauna;' how complete is that transition; and
if a well-defined zoogeographic boundary
does exist along the northern North Atlantic
island arc, what biological, historical and
oceanographic features maintain it?
Analysis of the available distributional
data on northern prosobranch gastropods
(Thorson 1944: 146-54) and northern lamelli-
branchs (Ockelmann 1958: 194-201), with
additions from the present survey and other
data, substantiates the casual observation
that a well-defined transition zone exists
between Iceland! and eastern Greenland. If
the 79 pan-boreal Atlantic prosobranch
species and the 70 pan-boreal Atlantic
lamellibranch species (which occur from
North America to Europe and along the
whole Greenland-Iceland—Faroes island arc)
are set aside, and the few species endemic
to a particular segment of the arc are like-
wise excluded, a substantial residue of North
American species and European species
remains. Not surprisingly, these species
groups are represented by decreasing num-
bers of species with the increasing distance
from North America and Europe (Table 4).
The faunal changes that occur may be
expressed in a striking manner by noting the
percentage of European species relative to
the total of European plus North American
species in the faunas of West Greenland,
East Greenland, Iceland and the Faroes.
These percentages are 22, 41, 88 and 100
respectively. The most dramatic shift occurs
as one progresses from East Greenland to
Iceland, and is caused principally by the
large increase (78) of European species and
only secondarily by a decrease (16) in North
American species. On zoogeographic
grounds, therefore, the island arc may be
considered as a region of transition between
the North American and European faunas;
if it is desirable to apply a boundary line
between these zoogeographic regions, the
line should be located between East Green-
land and Iceland. This problem should be
expanded and investigated more thoroughly
to determine whether or not corresponding
zoogeographic boundaries may be defined
for regions of greater depth. The whole
problem of zoogeographic limits of the deep
sea benthos is a particularly intriguing one.
1 | believe that such adjectives as “arctic”,
“subarctic’’, ‘boreal’, and “European” have been
applied much too extensively in the literature
on marine molluscs. Pseudo-problems arise when
one attempts to explain the presence of a species
in the Arctic, for example, that has been assigned
previously to a subarctic species group. In the
present context, “‘European’” and ‘‘North Amer-
ican” are used to characterize species whose
distributions extend beyond the Greenland-Ice-
land—Faroes arc to Europe or to North America.
The terms are meant to imply nothing about
species origins or about their migration routes,
and no problems therefore arise through their use.
Table 4
Species representation of geographic faunal groups of marine prosobranchs and lamelli-
branchs occurring near West Greenland, East Greenland, Iceland, and the Faroe Islands
West
Species Group Greenland
North American prosobranchs 27
North American lamellibranchs 16
European prosobranchs 5
European lamellibranchs Py
Per cent North American* 21
Per cent European 6
Per cent pan-boreal Atlantic 73
East Faroe
Greenland Iceland Islands
22 10 0
8 4 0
10 44 56
11 55 73
15 5 0
10 38 46
7§ 57 54
*Prosobranchs and lamellibranchs only and excluding localized endemic species.
Discussion
It is usually difficult, and often impossible,
to decide whether new regional records for
species are the results of more thorough and
effective collecting methods or if they signify
migrations of the species concerned. When
large or conspicuous species are found in
areas that have been well studied by previous
investigators, it is probable that faunal mi-
grations have occurred. Present examples
are the new records of Laeocochlis granosa
from near the Grand Banks, Neptunea satura
from near Iceland, and Megayoldia thraciae-
formis from the northern extremity of Baffin
Bay. On the other hand, new records of small
and inconspicuous species may not reflect
faunal migrations, although the possibility of
such migrations surely exists. Examples here
are the new records of Aclis walleri, Euli-
mella compactilis and Axinulus pygmaeus.
Natural range expansions of some marine
animals are well documented, and there is
every reason to believe that the zoogeogra-
phy of archibenthal and abyssal molluscs is
also dynamic. Our present concepts of
geographic distribution patterns of deep-
water marine molluscs are based on summa-
tions of all presumably authentic species
records accumulated over 50 to 100 years
or more. The extent to which these concep-
tual patterns reflect present reality is an
important question that deserves extensive
investigation.
Some aspects of the composition and re-
lationships of the Baffin Bay molluscan
fauna have been discussed previously
(Thorson 1951; Clarke 1963). The material
now available shows that the Baffin Bay
fauna is substantially an extension of the
Labrador Sea fauna but that it contains fewer
species. The presence of some endemic
mollusc species occurring in depths greater
than 300 fm, that is greater than the sill
depth of Davis Strait, suggests substantial
antiquity of isolation of that fauna. These
species are Acrybia glacialis Thorson, Colus
krampi (Thorson), and some other species
reported here that may be new, that is,
Proneomenia sp., Chaetoderma sp. and Ly-
onsiella sp. Presumed antiquity is in agree-
ment with the most recent estimates of age
for the termination of sea-floor spreading in
Baffin Bay and the formation of the Davis
Strait Sill, that is, about 60 million years ago
(Keen et al. 1972; see also Hyndman 1973).
Based on estimates of evolutionary rates
derived from studies of other regions, the
relative extent of endemicity in Baffin Bay is
22
lower than might be expected. Evolution may
well be slower in cold than in warm regions,
however, because as indicated by other ev-
idence (Dobzhansky 1950, general; Clarke
1965, molluscs), selection in cold regions is
primarily physical, whereas in warm regions
it is primarily biological. Additional geophys-
ical studies in Baffin Bay may well provide
a new basis for estimating probable evolu-
tionary rates in an arctic marine environment.
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23
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