Gastropods from Late Cretaceous Omagari and Yasukawa
hydrocarbon seep deposits in the Nakagawa area,
Hokkaido, Japan
ANDRZEJ KAIM, ROBERT G. JENKINS, and YOSHINORI HIKIDA
Kaim, A., Jenkins, R.G., and Hikida, Y. 2009. Gastropods from Late Cretaceous Omagari and Yasukawa hydrocarbon
seep deposits in the Nakagawa area, Hokkaido, Japan. Acta Palaeontologica Polonica 54 (3) 463–490. DOI: 10.4202/
app.2009.0042.
Sixteen gastropod species from two Campanian (Upper Cretaceous) hydrocarbon seep localities in Hokkaido, Japan are de−scribed. Seven species are new: the acmaeid limpet Serradonta omagariensis; three turbinids: Homalopoma abeshinaiensis,
Cantrainea yasukawensis, and C. omagariensis; the trochid Margarites sasakii; the seguenzioid Cataegis nakagawensis;
and the provannid Provanna nakagawensis. The most common species in the investigated localities are acmaeid limpets (S.
omagariensis), tiny turbinids (H. abeshinaiensis, C. yasukawensis, C. omagariensis), and provannids/hokkaidoconchids (P.
nakagawensis and Hokkaidoconcha hikidai). The Upper Cretaceous associations described here do not resemble Lower
Cretaceous associations known from other regions but are composed of species similar to gastropods from Recent hydrocar−
bon seeps and hydrothermal vents in the Northwestern Pacific. This strongly suggest that this region possesses a regional
pool of gastropods in chemosynthesis−based communities at least since Late Cretaceous time. The only group of gastropods
described here which has no Recent counterpart is the Hokkaidoconchidae. A comparison to gastropods from plesiosaur
falls and sunken wood of the same age and region strongly suggest that these invertebrate communities do not differ signifi−
cantly from the coeval hydrocarbon seep communities described herein.
Key wo r d s: Gastropoda, hydrocarbon seeps, Cretaceous, Hokkaido, Japan.
Andrzej Kaim [kaim@twarda.pan.pl], Instytut Paleobiologii PAN, ul. Twarda 51/55, PL−00−818 Warszawa, Poland;
Robert G. Jenkins [robertgj@ori.u−tokyo.ac.jp], HADEEP, Ocean Research Institute, University of Tokyo, 1−15−1
Minamidai, Nakano−ku, Tokyo 164−8639, Japan;
Yoshinori Hikida [nmhikida@coral.ocn.ne.jp], Nakagawa Museum of Natural History, Hokkaido 068−0835, Japan.
Received 28 April 2009, accepted 12 June 2009, available online 17 July 2009.

Introduction
The discovery of chemosynthesis−based communities wasprobably one of the biggest surprises in the marine biology of
20th century (Desbruyères et al. 2006). The basic source of
nourishment in such communities comes largely from micro−bial chemosynthetic processes due to sulfur and/or methane
oxidation (Van Dover 2000). There are three basic types ofsubstrates where these communities develop: hydrothermal
vents, cold seeps, and vertebrate falls. Sunken wood commu−
nities are also partially chemosynthetically fuelled (Kiel and
Goedert 2006a, b). Cold seeps develop in places where porewaters rich in methane, ammonia, and sulfide reach the sea
bottom. Most typically the seep communities appear in brine
seeps at the continental margins, subduction zones along con−vergent margins, and also over the salt diapirs (Van Dover
2000). Although Recent vent and seep communities have been
explored to a relatively large extent—including those fromJapanese waters (Kojima 2002; Sasaki et al. 2005)—but theirfossil record remains poorly known and therefore the histori−
cal development of chemosynthesis−based communities is still
Acta Palaeontol. Pol. 54 (3) 463–490, 2009of debate (Little and Vrijenhoek 2003; Campbell 2006; Kiel
and Little 2006). Fossil chemosynthesis−based associations
are relatively well researched in Japan (Majima et al. 2005)
but it mostly concerned their post−Cretaceous record. Recent
investigations on Upper Cretaceous hydrocarbon seep carbon−
ates from Hokkaido, Japan (Kaim and Jenkins 2008) revealed
well preserved and diverse fossil material of chemosynthesis−
based associations from this time interval. Although exotic
carbonates in the Cretaceous of Hokkaido were long−known toJapanese geologists (Hashimoto et al. 1967; Tanabe et al.
1977), their hydrocarbon seep origin had not been realized un−
til the 1990s. Seep carbonates were first identified in the
Mikasa region (Kanie et al. 1993), then in the Tappu area
(Kanie et al. 1996, Kanie 2000), and finally in the Nakagawa
region (Hikida et al. 2003). Previous taxonomic treatments ofthe fauna from hydrocarbon seep carbonates in Hokkaido con−cerned mainly bivalves (Kanie et al. 1993, 1996, 2000;
Amano et al. 2007; Kiel et al. 2008a), while gastropods re−mained poorly known. Some preliminary identifications were
provided by Hikida et al. (2003) and Jenkins et al. (2007a, b)
while first taxonomic description of gastropods from Creta−
DOI: 10.4202/app.2009.0042

464

ceous hydrocarbon seep carbonates in Hokkaido came from
Kaim et al. (2008a). However, that paper described exclu−
sively provannids and hokkaidoconchids and the remaining
gastropods were not covered. This paper provides descriptionof gastropods from two hydrocarbon seep localities in the
Nakagawa region: Omagari and Yasukawa. It also discusses
the importance of this fauna for deciphering the evolution ofchemosynthesis−based associations.
Institutional abbreviations.—DEPUT, Department of Earthand Planetary Sciences, Faculty of Science, University ofTokyo, Japan; NMM, Nakagawa Museum of Natural His−
tory, Nakagawa, Japan; NSMT, National Museum of Natureand Science, Tokyo, Japan (formerly National Science Mu−seum); ORI, Ocean Research Institute, University of Tokyo,
Japan; UMUT, University Museum, University of Tokyo,
Tokyo, Japan. ZPAL, Institute of Paleobiology, Polish Acad−emy of Sciences, Warszawa, Poland.
Other abbreviation.—s, standard deviation.

Material and methods
The gastropods described in this paper are from the Omagari
and Yasukawa seep sites located along Abeshinai river,
Nakagawa area, Hokkaido, Japan (Fig. 1), collected during
several field seasons and were also obtained from wet−siev−
ing of weakly consolidated muddy sediments (mesh size 0.5mm). Specimens were cleaned, mounted on stubs, coatedwith platinum, and examined on Hitachi S−2400S and Philips
XL20 scanning electron microscopes at DEPUT and ZPAL
respectively. A single specimen of Bathyacmaea cf. subnip−
ponica (Fig. 2A) was photographed without coating on the
SEM at NSMT, courtesy of Takenori Sasaki, with help byHiroshi Saito. The microstructure of Gigantocapulus sp. has
been investigated with a Hitachi S−4500 at ORI. Some speci−
mens were light−photographed in the photo−lab of ZPAL.
The photographs of Cantrainea nuda have been kindly pro−vided by Takenori Sasaki (UMUT).

Geological setting
Fossil hydrocarbon seep deposits are distributed in Hokkaido
along a meridional belt of outcrops of the Yezo Group. Thissequence is composed of marine−clastic deposits sedimented

ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

in the Yezo fore−arc basin along the western margin of a
subduction zone in the circum−northwestern Pacific during
the Cretaceous (Takashima et al. 2004). It is noteworthy thatthe oldest (Albian) seep carbonates are located in the south−
ern part of the belt (Utagoe and Pombetsu), a Cenomanianseep site in the Tappu area (Kanajirisawa) is located in the
middle part of the belt, and the youngest examples (Cam−panian) are located in the northern part of the belt in the
Nakagawa area. There are three published localities from thelatter region: Omagari, Yasukawa, and Gakkonosawa. The
Gakkonosawa seep carbonate (Kaim et al. 2008a) differsfrom the remaining two in the type of fossil preservation: thefossils from Gakkonosawa are silicified while the fossils
from Omagari and Yasukawa retain original mineralogy or
are re−crystallized into calcite. The samples from Gakkono−sawa are still being processed and the gastropods from thislocality will be published elsewhere. Both the Omagari and
Yasukawa carbonate bodies occur within upper part of theOmagari Formation and are dated as Campanian (Takahashi
et al. 2007). The Omagari Formation is characterized by al−
ternations of sandstone and sandy siltstone with some inter−calated gravel beds, and is interpreted as deposited at the in−terface of a continental−shelf margin and a continental slope(Jenkins et al. 2007b). Gastropods from the Omagari Forma−tion in the reaches of the Abeshinai river were previously
studied by Nagao (1932, 1939). However, it seems that the
majority of his material (Table 1) came from “normal” sedi−ments, although there could be two possible exceptions. It
seems likely that Ataphrus tesioensis Nagao, 1939 and Mar−garites sachalinensis Nagao, 1939 could belong to chemo−
synthesis−based associations as similar gastropods are de−scribed here. Unfortunately, Nagao’s (1932, 1939) localities
are only very briefly described and it is difficult to state if thegastropods were from seep carbonates. Preliminary identifi−
cations of gastropods from the Omagari site were provided
by Hikida et al. (2003) while Kaim et al. (2008a) reported
provannids and hokkaidoconchids from Omagari, Yasukawa,and Gakkonosawa.
Omagari.—The 10−meter−wide seep carbonate body forms asmall islet in the Abeshinai river near the mouth of its tribu−
tary, the Osoushinai river (Fig. 1D). The seep deposit yielded
large numbers of probable vestimentiferan worm tubes, abun−dant small gastropods and many small− to medium−sized bi−
valves. The seep carbonate in Omagari was first mentioned by
Hashimoto et al. (1967) who reported dense assemblage oftube−like trace fossils, which were later identified (Hikida etFig. 1. A. Geological map of Hokkaido, Japan, showing the distribution of Cretaceous chemosynthesis−based associations. Localities asterisked are authors’ ®
unpublished data. B. Location of Hokkaido on the Northwestern Pacific Coast (after Takashima et al. 2004). C. Gastropod−bearing fossil localities in the
Nakagawa area. Localities in circles are those of Nagao (1932, 1939), see also Table 1: N1, Sakaizawa; N2, left bank of the Abeshinai, south of Shibunnai;
N3, Ososinaizawa, a tributary of the Abesinai river; N4, Sibunnaizawa, a tributary of the Abesinai river an a point along the latter river, 300 m upstream; N5,
Abesinai river; N6, Middle course of the Abesinai river; N7, Abesinai river, about 100 m upstream from the junction with Sakaizawa. N5 and N6 (shaded)
are uncertain, the Nigorikawa locality is out of map range (south from the map), and two localities (“Omoshiroshibets, a tributary of the Abeshinai” and “asmall tributary of the Abesinai river, near the postal service station”) have not been recognized. Investigation of YH revealed that “Omoshiroshibets” is ap−
parently a locality in Enbetsu area and not along the Abeshinai River. D. The Omagari site with the gastropod−rich area indicated by an arrow. E. The
Yasukawa site with the gastropod−rich areas indicated by arrows.

(Santonian-Campanian)Jurassic accretionary complexes

Akita Creeku ZoneNio*
Gakkonosawa
Yasukawa
Tannosawa*
OmagariNio*

Wakkanbetsu

Sanjussensawa
Horokanai(Campanian)(Cenomanian)Cretaceous volcano-sedimentary
successions

HaboroHidakaBelt(Turonian and Coniacian)Cretaceous granitic rocks

Kanajirisawa

JAPAN SEA

Ultramafic rocks

44 N
Kamikinen*(Turonian)

Pombetsu

I DO
A
K K

(Albian)45°

Utagoe140E

40°(Albian)

35°

HO

135°

one
.Z

142 E

20°N

150°

145°

140°

ne
Kam uikotan Zo(Turonian/Santonian)

25°42 N

500 1000 km

PACI

Hobetsu*

30°

0

EAN
C
O
FIC

42 N
144 E

50°

Ido

A

130°

OKHOTSK SEA(Cenomanian)High-pressure-type
metamorphic rocks

120°E 125°

Blue: hydrocarbon seepOrange: plesiosaur fall
Green: wood falls
Purple: thought to be methane
seep, now uncertain, probably
reduced environment

Sorachi-Yezo
Belt(Coniacian)Upper Jurassic to Lower Cretaceous
volcano-sedimentary successions

465

Idonnapp

Oshima Be
lt

Paleozoic to Lower Cretaceous shelf
to continental sediments
Upper Cretaceous to Eocene
accretionary complexes

Nakagawa:
CampanianCretaceous–Paleocene forearc basin
sediments

Kam uik
otan Zone

KAIM ET AL.—SEEP GASTROPODS FROM CRETACEOUS OF HOKKAIDO, JAPANB

Nakagawa Museum of Natural History

Gakkonosawa River

Gakkonosawa seep
(Kaim et al. 2008)

Teshio River

Ch

Tann
o

ika

be

b

s

n
un

ai

Ri

ve

Riv

r

Abeshinai River

Ru

e
hib

er
N5
N6

D

Yasukawa seepsawa

N44 40 S
E142 0 S(Jenkins et al. 2007b)

Cr e ek

Omagari
Omagari seep
seep

N

N4

(Hikida et al. 2003)

N2
N3

Sh

ib

un

na

iR

Osoushinai River

ive

r

0

Wakkawenbetsu wood-fall r N1
(Kiel et al. 2009)
ive
uR
ets
b
n
e
1000 m
kka
Wa

N7

C

E
DOI: 10.4202/app.2009.0042

466

ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

Table 1. Late Cretaceous gastropods described by Nagao (1932, 1939) from the Nakagawa area. Original spelling retained.
Taxa

Locality

Nagao 1932
Tessarolax japonicus Yabe and Nagao, 1928

Sakaizawa, a tributary of Abeshinai river

Tessarolax acutimarginatus Nagao, 1932

Nigorikawa, a small tributary of the Abeshinai river

Rostellaria japonica Nagao, 1932

Omoshiroshibets, a tributary of the Abeshinai

Avellana problematica Nagao, 1932

Left bank of the Abeshinai, south of Shibunnai

Nagao 1939
Ataphrus tesioensis Nagao, 1939

A small tributary of the Abesinai river, near the postal service station

Margarites sachalinensis Nagao, 1939

Omosirusibetu, Ososinaizawa, tributaries of the Abesinai river

Natica (Lunatia) ainuana Nagao, 1939

Ososinaizawa, a tributary of the Abesinai river

Natica (Lunatia) denselineata Nagao, 1940

Sibunnaizawa, a tributary of the Abesinai river and a point along the latter river, 300 m
upstream from the mouth of its tributary, the Wakkawen

Dicroloma (Perissoptera) sp. indet

Abesinai river

Pyropsis sp. indet.

Middle course of the Abesinai river

Semifusus (Trochofusus) tuberculatus Nagao, 1939 Abesinai river, about 100 m upstream from the junction with Sakaizawa
Surculites fusoides Nagao, 1939

Omosirusibetu, a small tributary of the Abesinai river

Fusus volutodermoides Nagao, 1939

The Ososinaizawa, a tributary of the Abesinai river

Avellana problematica Nagao, 1932

Abesinai−gawa

Table2. Gastropods from the Omagari and Yasukawa seep sites and their Recent counterparts. In bold are species constituting 93% of each associa−
tion respectively.
Species in Omagari and Yasukawa

Yasukawa
Omagari num−
Yasukawa
Omagarinumber of
ber of speci−%%
specimens
mens

Related species from Recent chemosynthesis−
based communities off Japan (but see * and **)Bathyacmaea cf. subnipponica Sasaki,
Okutani, and Fujikura, 2003

8

0.7

1

0.4

Bathyacmaea subnipponica Sasaki, Okutani, andFujikura, 2003

Serradonta omagariensis sp. nov.

431

36

7

2.9

Serradonta vestimentifericola Okutani, Tsuchida,
and Fujikura, 1992

Homalopoma abeshinaiensis sp. nov.

269

22

–

–

Homalopoma laevigatum (Sowerby, 1914)

Cantrainea yasukawensis sp. nov.

–

–

134

55

Cantrainea nuda Okutani, 2001

Cantrainea omagariensis sp. nov.

310

26

–

–

Cantrainea nuda Okutani, 2001

Margarites sasakii sp. nov.

37

3.1

–

–

Margarites ryukyuensis Okutani, Sasaki, andTsuchida, 2000

Cataegis nakagawensis sp. nov.

4

0.3

–

–

Cataegis meroglypta McLean and Quinn, 1987*

Provanna nakagawensis sp. nov.

74

6.2

3

1.2

Provanna shinkaiae Okutani and Fujikura, 2002

Hokkaidoconcha hikidai Kaim,
Jenkins, and Warén, 2008

–

–

96

39

–

Neogastropoda indet.

–

–

1

0.4

?Oenopota ogasawarana Okutani, Fujikura andSasaki, 1993

?Sulcoactaeon sp.

–

–

1

0.4

Naticiform gastropod

24

2

–

–

?Retiskenea diploura Warén and Bouchet, 2001

Skeneiform gastropod

44

3.7

–

–

?Helicrenion reticulatum Warén and Bouchet,
1993**

Gastropoda indet. 1

1

0.1

–

–

–

Gastropoda indet. 2

–

0

1

0.4

–
–

Gigantocapulus sp.
TOTAL

–

0

1

0.4

1202

100

245

100

* known only from the Caribbean** known only from the Lau Basin? relation to species from the Omagari and Yasukawa sites uncertain

KAIM ET AL.—SEEP GASTROPODS FROM CRETACEOUS OF HOKKAIDO, JAPAN

al. 2003) as possible vestimentiferan worm tubes. The mostcomprehensive treatment of the Omagari seep has been pro−vided by Hikida et al. (2003) who preliminarily identified fos−sils from this locality. Kiel et al. (2008a) have recently re−viewed bivalves from the Omagari site noting the occurrencesof an unidentified solemyid, Acila (Truncacila) hokkaidoensis(Nagao, 1932), Nuculana sp., Nipponothracia cf. ponbetsen−
sis Kanie and Sakai, 1997, Thyasira sp., and a poorly pre−served lucinids. Kaim et al. (2008a) reported an unidentified
provannid gastropod which is described as Provanna nakaga−
wensis sp. nov. herein. For a full list of gastropods from this lo−
cality see Table 2.
Yasukawa.—The Yasukawa site consist of several meth−ane−influenced carbonate bodies distributed on a bank of theAbeshinai river (Fig. 1E) about 3 km downstream from theOmagari site (Jenkins et al. 2007b). Jenkins et al. (2007b) de−
scribed the locality in detail and also studied the distributionof fossils in the locality. Later, Jenkins et al. (2008) identified
biomarkers typical for anaerobic oxidation of methane fromthis site. Jenkins et al. (2007a, b) preliminarily identified sev−
eral fossils occurring at Yasukawa site. Amano et al. (2007)
described Nucinella gigantea Amano, Jenkins, and Hikida,2007 from this locality while Kiel et al. (2008a) reviewed theremaining bivalves including Acharax cretacea Kanie andNishida, 2000, Leionucula formosa (Nagao, 1930), Acila(Truncacila) hokkaidoensis (Nagao, 1932), Nuculana (Ezo−nuculana) mactraeformis Nagao, 1932, Propeamussium yu−
barense (Yabe and Nagao, 1928), Thyasira tanabei Kiel,
Amano, and Jenkins, 2008, and several poorly preserved
lucinids. Kaim et al. (2008a) reported an unidentified pro−vannid (Provanna nakagawensis sp. nov. herein) and Hok−kaidoconcha hikidai Kaim, Jenkins, and Warén, 2008. For afull list of gastropods from this locality see Table 2.

Systematic paleontology
Phylum Mollusca Linné, 1758
Class Gastropoda Cuvier, 1798
Order Patellogastropoda Lindberg, 1986
Superfamily Lottioidea Gray, 1840
Family Acmaeidae Forbes, 1850
Subfamily Pectinodontinae Pilsbry, 1891
Genus Bathyacmaea Okutani, Tsuchida, andFujikura, 1992
Type species: Bathyacmaea nipponica Okutani, Tsuchida, and Fujikura,
1992, by monotypy; Recent, Sagami Bay, Japan.

Discussion.—The genus concept is based mainly on radulacharacters (Sasaki et al. 2003). The shells of Bathyacmaea
are rather similar to shells of Pectinodonta Dall, 1882 and theonly, although rather tenuous difference lies in the central
position of the apex in Serradonta while in Pectinodonta it israther subcentral anteriorly. Therefore, without knowledge467

of the radula the delimitation is difficult. Both genera havespecies with robust cancellate ornamentation but Sasaki et al.
(2003) also described B. tertia Sasaki, Okutani, and Fujikura,
2003 with a smooth shell.
Stratigraphic and geographic range.—Recent hydrothermal
vents and hydrocarbon seeps in the Western Pacific. Upper
Cretaceous hydrocarbon seep deposits in Japan.

Bathyacmaea cf. subnipponica Sasaki, Okutani, andFujikura, 2003
Fig. 2.
2003 Bathyacmaea cf. nipponica Okutani, Tsuchida, and Fujikura,
1992; Hikida et al. 2003: 338, fig. 10: 3.
2007 Bathyacmaea cf. subnipponica Sasaki, Okutani, and Fujikura,
2003; Jenkins et al. 2007a: 371, fig. 2B, C.

Material.—Eight specimens from the Omagari site: six speci−
mens at UMUT and two at NMM including specimen NMM−
228 illustrated in Hikida et al. (2003). One specimen from
Yasukawa (UMUT MM29353) was already illustrated by
Jenkins et al. (2007a: fig. 2C). The specimen illustrated by
Jenkins et al. (2007a) on fig. 2B was mislabeled as collected at
the Yasukawa site, actually the specimen UMUT MM29352
came from the Omagari site (Fig. 2B herein).
Dimensions.—The largest specimen (NMM−228) is 5.9 mm
long, 4.5 mm high, and 2.8 mm high.
Description.—The shell is patelliform, oval in outline. The
shell width is about 76% and height is about 50% of its length
respectively. The shell surface is ornamented by regularly
spaced concentric annulations and irregular radial riblets.
The apex is relatively high, corroded, and situated slightly
anteriorly of the center at 47% of the shell length. The
microstructure is obliterated by diagenesis in the examined
specimens, however, shell seems to be composed of at least
three layers (Fig. 2D3).
Discussion.—The shells under consideration are most simi−
lar to the Recent B. subnipponica from the Nankai Trough,off Japan (Sasaki et al. 2003) in having a relatively high shell,
oval outline, irregular radial riblets, and sturdy concentric or−namentation. Taking into account the large temporal distanceand the imperfect preservation of the Cretaceous specimens
we leave the latter in open nomenclature.

Genus Serradonta Okutani, Tsuchida, and Fujikura,
1992
Type species: Serradonta vestimentifericola Okutani, Tsuchida, andFujikura, 1992, by monotypy; Recent, Sagami Bay, Japan.

Discussion.—The most striking shell character of Serradontadelimiting this genus from other acmaeids is the strongly elon−
gated and compressed shell that is an adaptation for life on
vestimentiferan tubes (Okutani et al. 1992; Sasaki et al. 2003).
The uneven aperture is caused by this way of attachment to thenarrow and rounded substrate.
Similar adaptations are known from other limpets bothfrom hydrothermal vents as well as normal environments.
Some lepetodrilid limpets have somewhat compressed shells
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ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

Fig. 2. The acmaeid gastropod Bathyacmaea cf. subnipponica Sasaki, Okutani, and Fujikura, 2003 from the Campanian (Upper Cretaceous) Omagari(A–C) and Yasukawa (D) seep sites in Hokkaido, Japan. A. NMM−228 in apical view. B. UMUT MM30143 in apical (B1), postero−lateral (B2), lateral (B3),and posterior views. C. UMUT MM30144 in apical (C1), lateral (C2), and anterior (C3) views. D. UMUT MM29353 attached to Cantrainea yasukawensis
sp. nov. in apical (D1) and lateral (D2) view; D3 is a cross section through the shell showing three layers obliterated by diagenesis.

when they live attached to tubeworms at hydrothermal vents(Desbruyères et al. 2006). Some lepetellids living on empty
polychaete tubes secrete shells of similar shape (Verrill 1880)
while some neolepetopsids are reported to change their shell
shape after changing substrate from mussel shells to worm
tubes (Warén and Bouchet 2009). The lottiid limpet Flexi−

tectura from the Ukrainian Miocene (Anistratenko and Ani−
stratenko 2007) has a very similar shell shape to Serradonta,
apparently as an adaptation for life on bryozoan branches(compare Anistratenko and Anistratenko 2007). Undoubtedly,
limpets acquired such an adaptation several times. Serradonta
is confined to the region of Japanese Islands and this narrow

KAIM ET AL.—SEEP GASTROPODS FROM CRETACEOUS OF HOKKAIDO, JAPAN

469

Fig. 3. The acmaeid gastropod Serradonta omagariensis sp. nov. from the Campanian (Upper Cretaceous) Omagari (A, B, D) and Yasukawa (C) seep sites in
Hokkaido, Japan. A. Holotype (UMUT MM29351) in apical (A1), lateral (A2), and anterior (A3) views. B. UMUT MM30145 in apical (B1), lateral (B2), andanterior views. C. UMUT MM30146 in apical (C1), lateral (C2), and posterior (C3) views. D. UMUT MM30147 in apical (D1) and lateral (D2) views; D3, illus−
trates layering of the shell while D4 is a cross section through shell showing two layers obliterated by diagenesis. Abbreviations: p, prismatic; cl, cross lamellar.

geographic distribution and ecological occurrence suggestthat the Recent and fossil species belong to the same genus.
Stratigraphic and geographic range.—Recent hydrocarbon
seeps off Japan. Upper Cretaceous hydrocarbon seep depos−
its in Japan.

Serradonta omagariensis sp. nov.
Fig. 3.
2003 Serradonta cf. vestimentifericola Okutani, Tsuchida, and Fuji−kura, 1992; Hikida et al. 2003: 338, fig. 10: 4, 5.
2007 Serradonta cf. vestimentifericola Okutani, Tsuchida, and Fuji−kura, 1992; Jenkins et al. 2007a: 371, fig. 2A.
2007 Serradonta sp.; Jenkins et al. 2007b: 134, fig. 5.1.
Etymology: After the type locality.
Holotype: UMUT MM29351 (Fig. 3A), almost complete shell lacking
protoconch.

Type locality: Omagari site, Nakagawa area, Northern Hokkaido, Japan.
Coordinates 44°39’ 26’’ N, 144°2’ 25’’ E.
Type horizon: Fossil hydrocarbon seep deposits of Omagari Formation,
Campanian, Upper Cretaceous.

Material.— 431 moderately to well preserved specimensfrom Omagari. 371 specimens at UMUT and 60 at NMM.
Seven specimens from Yasukawa (all housed at UMUT).
The specimen illustrated by Jenkins et al. (2007a) on fig. 2A
was mislabeled as collected from Yasukawa; actually the
specimen UMUT MM29351 (designated here as holotype)came from Omagari (Fig. 3A herein).
Dimensions.—The average shell length is 4.0 mm ± s 0.63,
shell width 1.8 mm ± s 0.25, and shell height 2.3 mm ± s 0.50
in the material of 41 specimens measured from Omagari site.
Diagnosis.—Serradonta−type shells with strongly compres−
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sed shell and uneven aperture with neither concentric nor ra−
dial ornamentation on any portion of the shell. S. vestimenti−
fericola Okutani, Tsuchida, and Fujikura, 1992 is ornamented
throughout the ontogeny and S. kanesunosensis Sasaki, Oku−
tani, and Fujikura, 2003 is ornamented only on the juvenile
shell. Serradonta omagariensis is usually higher than wide
while the Recent species are wider than high.
Description.—The shell is patelliform with elliptical aper−
ture. The shell width ranges 34–64% (average 46 ± s 5.7, n =41) of shell length. The apex is situated slightly subcentral
anteriorly (at 36–50% of shell length, average 44 ± s 4.5).
There is no ornamentation apart from concentric growthlines. The protoconch and inner surface of teleoconch are un−
known. The microstructure is obliterated by diagenesis in theexamined specimens but it seems to be composed of at least
one inner (possibly cross lamellar) layer and two (possibly
prismatic) outer layers (Fig. 3D3, D4).
Discussion.—The shell shape of Serradonta is heavily influ−
enced by its way of life on the worm tubes. It seems that theshell shape variation depends on the shape and size of thetubes. A preliminary survey of 41 specimens from the Oma−gari site shows a rather wide range of shell dimensions. In
spite of that the shells of S. omagariensis differs from otherspecies of the genus in being higher than wide. Moreover, allspecimens are of small size similarly to S. kanesunosensis(that is, however, slightly wider than S. omagariensis) while
S. vestimentifericola achieves a much larger size (Okutani etal. 1992). The size, however, may be determined by thesmaller size of the worm tubes for S. omagariensis andS. kanesunosensis. An independent character differentiating
the species is the timing of the appearance of ornamentation
during the ontogeny (see diagnosis). S. omagariensis is thesole species of Serradonta known from the fossil record. The
species is relatively common at the Omagari hydrocarbon
seep where great abundances of worm tubes are reported,
whereas it is relatively rare at the Yasukawa hydrocarbon
seep where worm tubes are uncommon (Jenkins et al. 2007a,b; see also Table 2).
Stratigraphic and geographic range.—Omagari and Yasu−
kawa hydrocarbon seeps in Nakagawa area of northern
Hokkaido, Japan. Campanian, Upper Cretaceous.

Order Vetigastropoda Salvini−Plawen, 1980
Superfamily Trochoidea Rafinesque, 1815
Family Turbinidae Rafinesque, 1815
Subfamily Ataphrinae Cossmann, 1915
Tribe Colloniini Cossmann, 1917
Remark.—Recently Gründel (2008) included Colloniini
Cossmann, 1917 as a tribe of Ataphrinae Cossmann, 1915.
Indeed some of the colloniins described below are quite simi−
lar to some Jurassic and Cretaceous ataphrins and they werepreliminary identified by Jenkins et al. (2007a, b) and Kaim
et al. (2008a) as such. The molecular evidence suggests (Wil−ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

liams et al. 2008) that colloniins should be considered as a
distinct superfamily of vetigastropods.

Genus Homalopoma Carpenter, 1864
Type species: Turbo sanguinaeus Linné, 1758, original designation; Re−cent, Mediterranean.

Discussion.—The concept of Homalopoma unites species
having small turbiniform anomphalous shells. The type spe−
cies has a shell with well developed spiral ornament but somespecies have only weak spiral ribs (e.g., H. baculum [Car−penter, 1864]) or even smooth shells (e.g., H. laevigatum[Sowerby, 1914]). Similar but consistently much larger are
shells of the seemingly closely related Cantrainea Jeffreys,
1883 (see discussion below). Here we include only a strongly
ornamented species in Homalopoma while two other, weakly
ornamented species are assigned to Cantrainea.
Distribution.—Homalopoma is a species−rich genus with aworldwide distribution. It occurs from shallow water tobathyal depths. Some species of Homalopoma (e.g., H. laevi−
gatum) are reported from sunken wood off Japan (Okutani
2000). An undescribed species occurs also at hot vent inMariana Arch (Anders Warén, personal communication2008). An unnamed fossil species of Homalopoma was re−ported by Gill et al. (2005) from Eocene–Miocene aged hy−
drocarbon seep deposits on Barbados and two other unnamed
species are reported from two Eocene hydrocarbon seeps of
Washington State, USA by Goedert and Squires (1990). An−other species, Homalopoma wattsi (Dickerson, 1916), hasbeen reported by Kiel (2008) from Eocene wood−fall associ−ation in Washington State, USA. Abundant occurrences of
Homalopoma domeniconii Moroni, 1966 are reported byMoroni (1966) from the Miocene “Calcare a Lucine” in Italy
which have been later identified to be seep carbonates(Taviani 1994; Peckmann et al. 1999). H. abeshinaiensis de−scribed below represents the oldest record of Homalopoma
reported so far from chemosynthesis−based communities.

Homalopoma abeshinaiensis sp. nov.
Fig. 4.
Etymology: After the Abeshinai River in which the Omagari seep car−bonate is located.
Holotype: UMUT MM30150, Fig. 4C, moderately preserved shell withno protoconch.
Type locality: Omagari site, Nakagawa area, Northern Hokkaido, Japan.
Coordinates 44°39’26’’ N, 144°2’25’’ E.
Type horizon: Fossil hydrocarbon seep deposits of the Omagari Forma−tion, Campanian, Upper Cretaceous.

Material.—269 moderately preserved specimens: 252 shells
at UMUT and 17 shells at NMM.
Dimensions.—The holotype is 5.26 mm high and 4.57 mm
wide.
Diagnosis.—Shell low turbiniform, whorls moderately in−flated, ornamented by numerous spiral ribs and strongly
prosocline collabral threads. Intersections of spiral and axial
ornamentation nodose. Nodes elongated according to the di−

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471

Fig. 4. The turbinid gastropod Homalopoma abeshinaiensis sp. nov. from the Campanian (Upper Cretaceous) Omagari seep site in Hokkaido, Japan.
A. UMUT MM30148 in lateral (A1), latero−apical (A2), and apical (A3) views; A4, juvenile whorl; A5, details of shell ornamentation. B. UMUT MM30149
in apertural (B1), lateral (B2), and umbilical (B3) views. C. Holotype (UMUT MM30150) in lateral (C1, C2) and apical (C3) views. D. UMUT MM30151 inlateral view. E. UMUT MM30152 in apertural (E1), lateral (E2), and umbilical (E3) views.

rection of collabral threads. No clear demarcation between
lateral flank and base of the shell. Base ornamented by nu−
merous spiral ribs. H. abeshinaiensis differs from other spe−
cies of Homalopoma in its clearly nodose intersections be−
tween spiral ribs and axial threads.

Description.—The protoconch is unknown. The shell is tur−biniform with numerous spiral ribs. The earliest preserved
whorls are ornamented by four spiral ribs but their number
increases to eight on the later flank and eight on the base. The
ribs are of similar strength although some secondaries are
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ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

Fig. 5. The turbinid gastropod Cantrainea yasukawensis sp. nov. from the Campanian (Upper Cretaceous) Yasukawa seep site in Hokkaido, Japan.
A. UMUT MM30153 in lateral view. B. UMUT MM30154 in lateral view (B1) and another view (B2) showing inclination of the aperture. C. UMUT
MM30155 in lateral view (C1) and another view (C2) showing inclination of the aperture. D. UMUT MM30156 in lateral view (D2) and another view (D1)showing inclination of the aperture. E. UMUT MM30157 in lateral view. F. Holotype (UMUT MM30158) in apertural (F1) and lateral (F2) views.
G. UMUT MM30159 in lateral view. H. UMUT MM30160 in lateral view. I. UMUT MM30161 in lateral view (I1) and details of ornamentation (I2).
J. UMUT MM30162, aggregation of three specimens and an operculum; J1, general view; J2, the operculum. K. UMUT MM30163 in lateral view (K1),shell microstructure (K2) including the inner nacreous (n) and fibrous prismatic (fp) layers, and details of shell ornamentation (K3).

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473

Fig. 6. The turbinid gastropod Cantrainea yasukawensis sp. nov. from the Campanian (Upper Cretaceous) Yasukawa seep site in Hokkaido, Japan.
A. UMUT MM30164 in lateral (A1), apertural (A2), and umbilical (A3) view; A4, details of inner lip. B. UMUT MM30154 in apical view. C. UMUT
MM30156 in apical view. D. UMUT MM30159 in apical view. E. UMUT MM30157 in apical view. F. UMUT MM30155 in latero−apical view. G. UMUT
MM30160 in apical view. H. Holotype (UMUT MM30158) in umbilical view. I. UMUT MM30153 in umbilical view.

weaker. The ultimate whorl is characterized by a slightly dip−ping suture line. The generating curve is circular, aperturetangential, and peristome uninterrupted. The outer lip issmooth. The inner lip is usually with a narrow callus andthere is no umbilicus but a shallow crescent−shaped depres−sion between the inner lip and first spiral rib on the base.
Discussion.—Homalopoma abeshinaiensis recalls numerous
Recent shallow−water Homalopoma−like collonins. However,the strongly ornamented species have usually no nodes on the
spiral ribs [e.g., H. nocturnum (Gould, 1861)] or the nodes oc−
cur only on primary ribs and are absent on the secondaries[e.g., H. amussitatum (Gould, 1861)]. H. abeshinaiensis isvery common at the Omagari seep but unknown so far from
Yasukawa. H. abeshinaiensis is rather small as for this genus.
Stratigraphic and geographic range.—Omagari hydrocar−
bon seep in Nakagawa area of northern Hokkaido, Japan.
Campanian, Upper Cretaceous.

Genus Cantrainea Jeffreys, 1883
Type species: Turbo peloritanus Cantraine, 1835, original designation;

originally described as fossil from Plio−Pleistocene of Sicily, later foundalso living in Mediterranean Sea and Bay of Biscay.

Discussion.—The concept of Cantrainea unites large Homa−
lopoma−like colloniids. Some authors consider Cantrainea
to be a subgenus of Homalopoma (e.g., Knight et al. 1960:
270). Recent authors, however, follow Marshall (1979) andaccept the full generic status of Cantrainea. Nevertheless,
Marshall (1979: 551) stated that the whole group of Homalo−poma−like gastropods should be assessed more critically. A
potentially good character for distinguishing Cantrainea and
Homalopoma in the fossil record is the presence of a concave
subsutural ramp in the former genus. The type species ofCantrainea and also some other species: Cantrainea pana−mense (Dall, 1908), C. inexpectata Marshall, 1979, C. jam−steci (Okutani and Fujikura, 1990), C. macleani Warén and
Bouchet, 1993, and C. yoyottei Vilvens, 2001 have a wide
ramp whereas C. nuda Okutani, 2001 is totally smooth apartfrom a finely pleated subsutural cord (Fig. 7G herein). The
latter species is known from a single specimen (Fig. 7G) and
its diagnosis is based solely on the shell characters. As al−
ready mentioned by Okutani (2001) the generic assignment
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474

of this species is tentative pending examination of the soft
body. The lack of concave subsutural ramp might have re−sulted from general simplification of the sculpture in this spe−
cies.
Distribution.—Cantrainea includes about a dozen large spe−
cies of colloniids from deep waters of different regions of all
world oceans. At least three species are known from chemo−
synthesis−based communities. C. jamsteci has been descri−bed from hydrothermal vent at the Minami Ensei Knoll(Ryukyu Islands, Japan) by Okutani and Fujikura (1990) andC. panamense has been recently reported from Concepción
hydrocarbon seep off Chile (Sellanes et al. 2008). C. mac−
leani has been described from a hydrocarbon seep on Louisi−
ana Slope but it has also been reported from a station that “isnot situated in the vicinity of any known hydrocarbon seep”(Warén and Bouchet 1993: 10) and therefore not an obligate
chemosynthetic community member. Although Okutani(2001) did not report any connection of C. nuda to chemo−
synthesis−based community, such community was describedindeed from “Depression B” of Minami Ensei Knoll by
Hashimoto et al. (1995). Therefore, it seems to be most likelythat C. nuda is a member of such community. A single occur−
rence of Cantrainea from ancient chemosynthetic−based as−sociations has been reported from the Miocene Freeman’s
Bay Limestone on Trinidad (Gill et al. 2005).

Cantrainea yasukawensis sp. nov.
Figs. 5, 6.
2007 Ataphridae gen. et sp. indet.; Jenkins et al. 2007a: 8, fig. 5: 2.
2007 ataphrid gastropod; Jenkins et al. 2007b: 371, fig. 2c.
Etymology: After the type locality.
Holotype: UMUT MM30158, Figs. 5F and 6H, well preserved shellwithout protoconch.
Type locality: Yasukawa site, Nakagawa area, Northern Hokkaido, Ja−pan. Coordinates 44°40’37’’ N, 142°1’27’’ E.
Type horizon: Ancient hydrocarbon seep deposits of Omagari Forma−tion, Campanian, Upper Cretaceous.

Material.—134 moderately to well preserved specimens with−out protoconchs.
Dimensions.—The holotype is 3.59 mm high and 3.9 mm
wide.
Diagnosis.—Shell turbiniform with flat−topped or slightly
concave ramp at the suture. The upper part of the lateral flankslightly concave. Growth lines strongly prosocline. Spiral or−
namentation variable. C. yaskukawensis is much smaller
than any living species of Cantrainea and also smaller that C.
omagariensis described below. Moreover, it has a higher ul−
timate whorl in comparison to its width than C. omaga−
riensis. C. yasukawensis is also much smaller than the simi−
larly smooth−shelled Recent C. nuda Okutani, 2001; it differs
also in having a subsutural ramp rather than a pleated cord
and no knob on the inner lip of the aperture that is character−istic for C. nuda (Fig. 7G).
Description.—The protoconch is unknown. The shell is tur−biniform with variable spiral ornamentation. The most typi−

ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

cal example (see holotype, Figs. 5F and 6H) has a wide con−cave subsutural ramp and the base demarcated by a weak andrather rounded angulation. Some other specimens have a pat−tern of delicate faint ribs (Fig. 5B, C) and the base demar−cated by clear angulation at some specimens accompanied bya spiral rib (Fig. 5E, H). Some shells of C. yasukawensis lackany ornament apart from a narrow subsutural ramp (Figs. 5K,
6A). However, even on these smooth specimens there aresome spiral undulations visible under higher magnification(Fig. 5K3). The shell wall is relatively thick and bi−layered.
Inner nacreous layer is three times thicker than the outer pris−
matic layer. The ultimate whorl is characterized by slightly
dipping suture line. The generating curve is circular, aperturetangential, and peristome uninterrupted. The outer lip issmooth. The inner lip has usually a narrow callus and there isno umbilicus. In some specimens, especially these smooth−shelled, there is a callosity extended over the umbilical area
(Fig. 5F). Apertural elaborations are absent. The operculum
is calcareous and concentric in the visible part (Fig. 5J).
Discussion.—C. yasukawensis is a species with highly vari−able shell ornamentation. Such plasticity in shell morphology
is also observed in other gastropods inhabiting chemosyn−
thesis−based communities and the most conspicuous examples
are those of provannid gastropods: Provanna variabilis Warén
and Bouchet, 1986 from Recent hydrothermal vents on East
Pacific Rise and Provanna antiqua Squires, 1995 from Paleo−
gene hydrocarbon seeps in Washington State (Squires 1995).
Paskentana paskentaensis (Stanton, 1895) from Early Creta−
ceous seep associations is another example of highly variable
species (Kiel et al. 2008). C. yasukawensis is common in theproximity of methane influenced carbonate bodies and is alsopresent in the peripheral areas of the hydrocarbon seep (Jen−kins et al. 2007a). This gastropod was preliminarily identified
by Jenkins et al. (2007a, b) as an ataphrid and after a detailed
examination it seems that Cantrainea is the best place for it al−though the latter genus includes mostly much larger collonins.
C. yasukawensis is strikingly similar to the Recent C. nuda.
The latter species differs from C. yasukawensis especially inhaving a distinctive knob on the inner lip (Okutani 2001). The
other possible place for C. yasukawensis is Homalopoma
which includes small− and medium sized collonins. The spe−
cies of Homalopoma, however, have usually evenly convex
shells with no concave subsutural ramp.
Stratigraphic and geographic range.—Yasukawa hydrocar−
bon seep in Nakagawa area of northern Hokkaido, Japan.
Campanian, Upper Cretaceous.

Cantrainea omagariensis sp. nov.
Fig. 7A–F.
2008 ataphrid gastropod; Kaim et al. 2008b: 100, fig. 3h.
Etymology: After the type locality.
Holotype: UMUT MM30166, Fig. 7B, moderately preserved shell withno protoconch.
Type locality: Omagari site, Nakagawa area, Northern Hokkaido, Japan.
Coordinates 44°39’26’’ N, 144°2’25’’ E.

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475

Fig. 7. Turbinid gastropods of the genus Cantrainea from chemosynthesis−based communities. A–F. Cantrainea omagariensis sp. nov. from Campanian(Upper Cretaceous) Omagari seep site in Hokkaido, Japan. A. UMUT MM30165 in apical (A1), umbilical (A2), lateral (A3), and apertural views (A4).
B. Holotype (UMUT MM30166) in apical (B1, B5), lateral (B2, B3), and latero−apical (B4) views. C. UMUT MM30167 in lateral (C1) and apical (C2)views. D. UMUT MM30168; details of inner lip (D1), apertural (D2) and umbilical (D3) views. E. UMUT MM30169 in lateral view. F. UMUT MM30170
in apical view. G. Recent Cantrainea nuda Okutani, 2001 from “depression B” of the Minami Ensei Knoll, Okinawa Trough, Japan (NSMT−Mo 73040) in
lateral (G1), apical (G2), and umbilical (G3) views; G4, details of inner lip.

Type horizon: Fossil hydrocarbon seep deposits of Omagari Formation,
Campanian, Upper Cretaceous.

Material.—310 moderately preserved specimens without
protoconchs: 225 at UMUT and 85 at NMM, all from theOmagari site.
Dimensions.—The holotype is 4 mm high and 4.66 mm wide.
Diagnosis.—Shell low turbiniform, moderately inflated.
Surface smooth apart from narrow subsutural ramp. Growthlines strongly prosocline. C. omagariensis is slightly larger
than C. yasukawensis but smaller than any other species ofCantrainea. C. omagariensis differs also from C. yasuka−
wensis in having a lower ultimate whorl in comparison to its
width. C. omagariensis is smaller than C. nuda Okutani,
2001 and differs also in having a subsutural ramp rather
than a pleated cord and no knob on the inner lip.
Description.—The protoconch is unknown. The shell is tur−
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476

biniform, smooth apart from a narrow subsutural ramp. The
transition between lateral flank and the base is rounded withno demarcation. The shell wall is relatively thick and bi−lay−ered; the inner layer is nacreous and the outer layer is pris−
matic. The ultimate whorl is characterized by a slightly dip−ping suture line. The generating curve is circular, aperturetangential, and peristome uninterrupted. The outer lip issmooth. The inner lip is poorly preserved in all available
specimens but it seems to be narrow. The umbilicus is absent
although in some specimens a poorly developed umbilicalchink is visible. The latter feature may have resulted, how−ever, from erosion of the inner lip.
Discussion.—C. omagariensis is very similar to C. yasuka−
wensis. The latter species, however, is smaller and much morevariable morphologically, especially in respect to its spiral or−
namentation. C. omagariensis has a much more stable mor−
phology and is represented only by smooth shells. A similar
species is known from a single specimen found at “a small
tributary of the Abesinai−gawa” (Abeshinai River) in the
Nakagawa area from rocks of Senonian age (Nagao 1939:
215); Ataphrus tesioensis Nagao, 1939 differs from C. omaga−
riensis in lacking subsutural ramp and in having “...prominent
bundles of lines of growth near the suture, with numerous lon−
gitudinal impressed lines...” (Nagao 1939: 214), a feature notobserved on our specimens. Further studies are needed to sub−stantiate relation between these two species. C. omagariensis
is very common at the Omagari seep site. A similar althoughpoorly preserved shell has been reported from a plesiosaur fallassociation by Kaim et al. (2008b). Another similar shell has
been reported by Kiel et al. (2009) as “low−spired skeneiform
gastropod” from the Upper Cretaceous Akita Creek wood−fallassociation (Kiel et al. 2009: 77).
Stratigraphic and geographic range.—Omagari hydrocar−
bon seep in Nakagawa area of northern Hokkaido, Japan.
Campanian, Upper Cretaceous.

Family Trochidae Rafinesque, 1815
Genus Margarites Gray, 1847
Type species: Trochus helicinus Fabricius 1780 (? = Turbo helicinus
Phipps, 1774) by original designation pro Margarita Leach, 1819 (pre−occupied); Recent, Arctic Sea.

Margarites sasakii sp. nov.
Fig. 8.
2003 Margarites sp.; Hikida et al. 2003: 338, fig. 10: 1, 2.
Etymology: In honour of Dr. Takenori Sasaki.
Holotype: UMUT MM30174, Fig. 8D, moderately preserved shell with−out protoconch.
Type locality: Omagari site, Nakagawa area, Northern Hokkaido, Japan.
Coordinates 44°39’26’’ N, 144°2’25’’ E.
Type horizon: Fossil hydrocarbon seep deposits of Omagari Formation,
Campanian, Upper Cretaceous.

Material.—37 moderately to poorly preserved specimensfrom the Omagari site; 35 at UMUT and two at NMM al−
ready illustrated by Hikida et al. (2003).

ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

Dimensions.—The holotype is 9.42 mm high and 12.86 mm
wide; NMM 229 is 10.85 mm high and 12.7 mm wide. Notethat both shells are incomplete.
Diagnosis.—Shell turbiniform, whorls inflated. Juvenile andadolescent whorls ornamented by spiral cords present bothon the lateral flank and the base. Umbilicus absent. M.
sasakii differs from other species of the genus by the absenceof an umbilicus.
Description.—The protoconch is not preserved. The shell isturbiniform with a dark−brown amorphous outermost layer(Fig. 8B3). This might be a re−crystallized calcitic outer layer(Kiel and Goedert 2007) or even fossilized periostracum. Ju−
venile whorls are ornamented by spiral cords. There are fourribs at the lateral flank, one on the demarcation with the baseand at least four on the base. The ribs fade away at the termi−
nus being only weak undulations crossed by strongly en−
hanced prosocline growth lines. Some of these structures areapparently growth interruptions. The generating curve is cir−cular, aperture tangential, and peristome uninterrupted. Ap−
ertural elaborations are absent.
Discussion.—The shells under consideration are difficult toclassify as they could be included in many different veti−
gastropod genera. We preliminarily classify them as Marga−
rites pending better preserved material. M. sasakii differs fromother species of Margarites by lacking an umbilicus and pos−sessing spiral cords also on the base. However, the remaining
gross morphology strongly recollects M. ryukyuensis Okutani,
Sasaki, and Tsuchida, 2000 from a Recent chemosynthesis−
based community in the Okinawa Trough (Okutani et al.
2000). The other similar genus is the seguenzioid Cataegis
McLean and Quinn, 1987 that lacks an umbilicus but usuallypossesses much stronger ornamentation (see e.g., McLean and
Quinn 1987; Hickman and McLean 1990; Warén and Bouchet
1993; Fu and Sun 2006). Another similar genus is the trochid
Pseudotalopia Habe, 1961, which again possesses an umbili−
cus and much more delicate ornamentation (Okutani 2000).
M. sasakii is the largest vetigastropod recovered so far fromthe Omagarii seep site. It is usually poorly preserved but easily
identifiable due to its dark brown outer layer.
Stratigraphic and geographic range.—Omagari hydrocar−
bon seep in Nakagawa area of northern Hokkaido, Japan.
Campanian, Upper Cretaceous.

Superfamily Seguenzioidea Verrill, 1884
Family Chilodontidae Wenz, 1938
Subfamily Cataeginae McLean and Quinn, 1987
Genus Cataegis McLean and Quinn, 1987
Type species: Homalopoma finkli Petuch, 1987 as senior synonym of
Cataegis toreuta McLean and Quinn, 1987; original designation. Re−
cent, Caribbean.

Discussion.—Cataegis was primarily described as a trochidof uncertain familial affinity (McLean and Quinn 1987;
Hickman and McLean 1990). Bouchet et al. (2005) included
Cataeginae as a subfamily of Chilodontidae Wenz, 1938 in

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477

Fig. 8. The trochid gastropod Margarites sasakii sp. nov. from the Campanian (Upper Cretaceous) Omagari seep site in Hokkaido, Japan. A. UMUT
MM30171 in apertural (A1) lateral (A2, A3), umbilical (A4), and apical (A5) views. B. UMUT MM30172 in apical (B1) and lateral (B2) views; B3, cross sec−tion through outer layer. C. Juvenile UMUT MM30173 in apical (C1), and lateral (C2–C4) views. D. Holotype (UMUT MM30174) in apical (D1) and lateral(D2–D4); note change in ornamentation in D4. E. NMM 229 in apical (E1), apertural (E2), and umbilical (E3) views.

Seguenzioidea. Recent molecular investigations by Kano
(2008) revealed that Cataegis indeed goes to Seguenzioidea;

the remaining family Chilodontidae appears to be a poly−phyletic taxon and needs further investigations.
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ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

Fig. 9. The seguenzioid gastropod Cataegis nakagawensis sp. nov. from the Campanian (Upper Cretaceous) Omagari seep site in Hokkaido, Japan.
A. Holotype (UMUT MM30175) in apertural (A1), lateral (A2), and umbilical (A3) views. B. UMUT MM30176 in apical (B1), lateral (B2, B3), andlatero−apical (B4) views. C. UMUT MM30177 in apical (C1), lateral (C2, C3), latero−umbilical (C4), and latero−apical (C5) views.

Distribution.—Cataegis includes deep water species known
from the Caribbean (McLean and Quinn 1987; Hickman and
McLean 1990; Warén and Bouchet 1993) and from the Pacific(McLean and Quinn 1990; Fu and Sun 2006). At least one spe−cies, C. meroglypta McLean and Quinn, 1987 is known fromhydrocarbon seep on the Louisiana Slope (Warén and Bouchet
1993; García 2002; Gill et al. 2005). Cataegis sp. has also
been found in seeps off Costa Rica (Anders Warén, personalcommunication 2009). Gill et al. (2005) reported occurrencesof C. meroglypta from Cenozoic Caribbean seep carbonates.
The species has been identified in the Oligocene or Early Mio−
cene Sub−Oceanic Fault Zone seeps of Barbados and also the
Miocene Freeman’s Bay Limestone seep fauna (Gill et al.
2005). Moroni (1966) reported Phasianema taurocrassum
Sacco, 1895 from the Miocene “Calcare a Lucine” (seep car−bonates according to Taviani 1994 and Peckmann et al. 1999)
which is quite similar to Cataegis.

Cataegis nakagawensis sp. nov.
Fig. 9.
Etymology: After Nakagawa town, located close to the type locality.
Holotype: UMUT MM30175, Fig. 9A, moderately preserved shell withno protoconch.

Type locality: Omagari site, Nakagawa area, Northern Hokkaido, Japan.
Coordinates 44°39’26’’ N, 144°2’25’’ E.
Type horizon: Fossil hydrocarbon seep deposits of Omagari Formation,
Campanian, Upper Cretaceous.

Material.—Four moderately preserved specimens without
protoconchs.
Dimensions.—The holotype is 4.1 mm high and 4.91 mm
wide.
Diagnosis.—Shell turbiniform, whorls ornamented withbeaded spiral cords. Two of the cords form spiral keels on thelower part of the flank. C. nakagawensis differs from otherspecies of the genus by having two distinctly keeled cords.
Description.—The protoconch is not preserved. The shell isturbiniform with whorls ornamented by six spiral cords. Twoof them are stronger transforming into two keels. The lower
keel is located at the angulation demarcating the flank fromthe base, while the other one is located slightly below the midpart of the flank. There are three cords above the upper keel
and one cord between the keels. The base is ornamented by
five beaded spiral cords. There is no umbilicus and the aper−
ture is poorly preserved.
Discussion.—The shells under consideration are provision−

KAIM ET AL.—SEEP GASTROPODS FROM CRETACEOUS OF HOKKAIDO, JAPAN

479

Fig. 10. The provannid gastropod Provanna nakagawensis sp. nov. from the Campanian (Upper Cretaceous) Omagari (A–D) and Yasukawa (E–G) seepsites in Hokkaido, Japan. A. Holotype (UMUT MM30178) in apertural (A1), lateral (A2), and apical (A3) views. B. UMUT MM30179 in apertural (B1), lat−eral (B2), and (B3) views. C. UMUT MM29362 in apertural view. D. UMUT MM30180 in lateral (D1, D2) and apical (D3) views. E. UMUT MM30181 inapertural view. F. UMUTMM30182in lateral (F1) and apical (F2) views. G. UMUT MM19363 in lateral (G1) and apical (G2) views.

ally classified as Cataegis because they lack an umbilicus
and posses strong spiral cords on the flank and also on thebase. Cataegis has not been noted so far from Japan. The
nearest extant occurrences are C. leucogranulata from Tai−wan (Fu and Sun 2006) and C. celebesensis from Indonesia(McLean and Quinn 1987).
Stratigraphic and geographic range.—Omagari hydrocar−
bon seep in Nakagawa area of northern Hokkaido, Japan.
Campanian, Upper Cretaceous.

Order Caenogastropoda Cox, 1959
Superfamily Abyssochrysoidea Tomlin, 1927
Family Provannidae Warén and Ponder, 1991
Genus Provanna Dall, 1918
Type species: Trichotropis (Provanna) lomana Dall, 1918. Recent; US
Pacific Coast; by monotypy.

Provanna nakagawensis sp. nov.
Fig. 10.
2008 Yasukawa provannid; Kaim et al. 2008a: 427, fig. 3D, E, I.
2008 Omagari provannid; Kaim et al. 2008a: 427, fig. 3F, J.
Etymology: After Nakagawa town, located close to the type locality.
Holotype: UMUT MM30178, Fig. 10A, moderately preserved shellwith no protoconch.
Type locality: Omagari site, Nakagawa area, northern Hokkaido, Japan.
Coordinates 44°39’26’’N, 144°2’25’’E.
Type horizon: Fossil hydrocarbon seep deposits of the Omagari Forma−tion, Campanian, Upper Cretaceous.

Material.—76 moderately to poorly preserved specimens
without protoconchs from the Omagari site and three poorly
preserved specimens from the Yasukawa site.
Dimensions.—The holotype is 5.36 mm high and 3.35 mm
wide.
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ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

Fig. 11. The hokkaidoconchid gastropod Hokkaidoconcha hikidai Kaim, Jenkins, and Warén, 2008 from the Campanian (Upper Cretaceous) Yasukawa
seep site in Hokkaido, Japan. A. Holotype (UMUT MM29391) in lateral view. B. UMUT MM30183 in lateral (B1), apertural (B2), and apical (B4) views;
B3, cross section through the shell displaying inner and outer prismatic (p) layers and middle cross−lamellar (cl) layer. C. UMUT MM30184 in apertural
view (C1) and details of ornamentation (C2).

Diagnosis.—Shell of small size, rather high, moderately in−flated. Spiral ornament consists of two median prominentribs and additional weaker rib adapically to the primary ribs.
Spiral ribs intersected by orthocline axial ribs, which may
fade away later in ontogeny. Blunt nodes present at intersec−
tions of spiral and axial ribs.

(UMUT MM 29514) reported by Kiel et al. (2009: fig. 3E)
from the Upper Cretaceous Akita Creek wood−fall associa−
tion from Hokkaido belongs to P. nakagawensis. Also theprovannid specimens reported by Kaim et al. (2008a) as“Gakkonosawa provannid” from Cretaceous Gakkonosawa
seep carbonate may belong to P. nakagawensis.

Description.—The shell is of small size, thin, melanoid torissoid in shape with strong spiral and axial sculpture. In
some specimens the axial sculpture is weak or absent. The
protoconch is unknown. Spiral ribs are strong on juvenile
whorls, two prominent ones and one weaker, which occur
adapically of the other two. There might be an additional rib
appearing abapically of the prominent ribs on some larger
shells. The base is demarcated from the lateral flank by anadditional strong spiral rib. The base is usually ornamented
by 2–3 spiral ribs. Axial ribs orthocline, equally strong as
spirals on the juvenile whorls and fading out on the adoles−
cent whorls in some specimens. Aperture poorly preservedon the available specimens.

Stratigraphic and geographic range.—Omagari and Yasu−
kawa hydrocarbon seeps in Nakagawa area of northern Hok−kaido, Japan. Campanian, Upper Cretaceous.

Discussion.—This thin−shelled species, although fairly com−
mon at the Omagari site, is usually poorly preserved. In thisrespect it is similar to many Recent species of Provanna.
P. nakagawensis is most similar to Recent P. shinkaiae
Okutani and Fujikura, 2002 from the Japan Trench. The lat−ter species is also thin−shelled and ornamented by two promi−
nent ribs but lacks the weaker adapical rib (Okutani andFujikura 2002). Moreover, P. shinkaiae has beaded or spiny
intersections of spiral and axial ribs, while in P. nakaga−
wensis blunt nodes appear there. Other similar species in−clude P. pacifica (Dall, 1908) and P. goniata Warén and
Bouchet, 1986 known from the eastern Pacific; both, how−ever, are much larger than P. nakagawensis (Warén and
Bouchet 1986). It is likely that one of the provannid shells

Family Hokkaidoconchidae Kaim, Jenkins, andWarén, 2008
Genus Hokkaidoconcha Kaim, Jenkins, and Warén,
2008Type species: Hokkaidoconcha tanabei Kaim, Jenkins, and Warén,
2008; Kanajirisawa Creek, Tappu area, Hokkaido, Japan; Middle Ceno−
manian (Late Cretaceous); original designation.

Hokkaidoconcha hikidai Kaim, Jenkins, and Warén,
2008
Fig. 11.

Remarks.—Hokkaidoconcha hikidai has been recently de−scribed by Kaim et al. (2008a). Since preparation of the latter
paper we have found additional specimens of this species.
Regrettably none of these has the protoconch preserved.
Nevertheless we found some specimens in the seep periphery(see zonation of the Yasukawa seep in Jenkins et al. 2007b)with original shell microstructure preserved. The shell con−sists of a thin prismatic outer layer, a thick cross−lamellar
middle layer, and a moderately thick prismatic inner layer(Fig. 11B3), a shell layer organization known from Provan−
nidae (Kiel 2004).

KAIM ET AL.—SEEP GASTROPODS FROM CRETACEOUS OF HOKKAIDO, JAPANSuborder Neogastropoda Thiele, 1929
Neogastropoda indet.
Fig. 12D.

Material.—Single incomplete shell (UMUT MM30188) from
Yasukawa partially embedded in the rock matrix.
Dimensions.—The visible part of the shell UMUT MM30188
is 4.44 mm high and 3.77 mm wide.
Description.—Only lateral flank of half−whorl is preserved.
The shell possesses a wide ramp at the suture. There areseven sturdy orthocline axial ribs and approximately twelve
much weaker spiral ribs on the visible part of the shell. The
ramp is demarcated from the flank by an additional spiral rib
ornamented with blunt nodes appearing at the intersections
with axial ribs. There is an additional spiral rib on the ramp
surface. The shell is elongated abapically suggesting thepresence of a siphonal notch or channel.
Discussion.—The shell under consideration is too incom−
pletely preserved to be assigned to any genus or species.
There are similar neogastropods known from Recent seep/vent communities off Japan. Especially similar are somespecies of Oenopota described by Okutani and Fujikura(1992) and Okutani et al. (1993). A similar species from an
Oligocene seep carbonate in Washington State has beenclassified by Kiel (2006) as Benthomangelia? sp. The spe−
cies under consideration differs both from the Recent Japa−
nese and Oligocene American species in having orthocline
rather than opisthocyrt axial ribs. It should be stated here,
however, that there is also a number of shallow water
neogastropods in the Cretaceous to which the Yasukawa
specimen can be related.

481

The inner lip is narrow. A narrow umbilical chink is pres−ent. Neither teeth nor other apertural elaborations are visi−
ble.
Discussion.—Sulcoactaeon is a genus known so far from
Bajocian to Valanginian times (Kaim 2004) although it isconsidered by some authors (Bandel et al. 2000) as a subge−
nus of the Recent Bullina (family Bullinidae). The most im−
portant shell character of Bullinidae is the absence of teeth orcolumellar plications on the inner lip. Such features are notobserved at the specimen under consideration. Nevertheless,due to generally poor preservation, there is a possibility thatthese features are not preserved in our specimen and that is
why we classified it as Sulcoactaeon with some hesitation.
Sohl (1964) described some species of Acteon and Troostella
from Upper Cretaceous shallow water sediments of the US
Gulf Coast which have an oblique low fold on the columellawith which later merges—and is not expressed on the innerlip. Our specimen may also be related to this group. The un−derstanding of relations between fossil groups of acteonel−loids is still rather limited and out of scope of this paper. Kiel
(2006) described similar species from Oligocene cold seep
carbonates of Washington State as Acteon sp. He reported apresence of “...weak plication at base” (Kiel 2006: 129) in his
specimen.

Naticiform gastropod
Fig. 13.

Material.—24 specimens from Omagari site: 23 specimens
at UMUT and one at NMM.
Dimensions.—The best preserved shell UMUT MM30190(Fig. 13B) is 1.96 mm high and 2.04 mm wide.

Subclass Heterobranchia Gray, 1840
Order Heterostropha Fischer, 1885
Superfamily Acteonelloidea Gill, 1871
Family Bullinidae Gray, 1850
Genus Sulcoactaeon Cossmann, 1895

Description.—The shell is small, globose, smooth apart fromprosocline growth lines. Early whorls are poorly preserved
but the protoconch is apparently orthostrophic. Teleoconch
consists of 3–3.5 inflated whorls with incised suture. Aper−
ture is circular and tangential. No aperture elaborations arevisible. Umbilicus is absent.

Type species: Actaeonina striato−sulcata Zittel and Goubert, 1861;
Glos, Normandy, France; ?Oxfordian (Late Jurassic); original designa−tion.

Discussion.—The shells under consideration are difficult toclassify due to their poor preservation. The small size andtangentially located circular aperture may suggest that theshells belong to neomphalid Retiskenea. The specimens fromthe Omagari site are similar in gross morphology to the Re−
cent Retiskenea diploura Warén and Bouchet, 2001 living in
the Japan Trench (Okutani and Fujikura 2002). The latter
species, however, possesses slit−like umbilicus, a characternot observed in our specimens. Similar is also Retiskenea
statura (Goedert and Benham, 1999) from Eocene andOligocene cold seep carbonates of Western Washington(Goedert and Benham 1999, Kiel 2006, Campbell et al.
2008). The state of the umbilicus in R. statura is not reported
by any of the abovementioned authors and the published il−lustrations are not conclusive on that matter. It seems, how−ever, that there is no umbilicus in the holotype of Goedert
and Benham (1999: fig. 2A) and the specimen described by?Sulcoactaeon sp.
Fig. 12A.

Material.—Single incomplete shell (UMUT MM30185) from
Yasukawa.
Dimensions.—The shell UMUT MM30185 is 2.96 mm highand 1.41 mm wide.
Description.—The shell is broadly spindle−like, 1.41 times
as high as broad. Early whorls are poorly preserved. Teleo−
conch whorls are ornamented by numerous spiral furrows.
The last whorl possesses a narrow subsutural ramp and two
furrows just below the ramp. All other furrows (approx. 12)
are present in the abapical part of the whorl. The density of
the furrows increases abapically. The aperture is D−shaped.

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ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

Fig. 12. Gastropods from the Campanian (Upper Cretaceous) Omagari (B) and Yasukawa (A, C, D) seep sites in Hokkaido, Japan. A. ?Sulcoactaeon sp.
(UMUT MM30185) in apertural (A1), lateral (A2), and apical (A4) views; A3, close up of the aperture. B. Gastropoda indet. 1 (UMUT MM30186) in aper−
tural (B1), lateral (B2), and apical (B3) views. C. Gastropoda indet. 2 (UMUT MM30187) in apertural (C3), lateral (C4), and apical (C5) views; C1, fibrousprismatic shell outer layer, C2, cross lamellar inner layer. D. Neogastropoda indet. (UMUT MM30188) in lateral (D1) and apical (D2) views.

Kiel (2006) (Steffen Kiel, personal communication 2009).
Campbell et al. (2008) reported a species Retiskenea? kieli
Campbell, Peterson, and Alfaro, 2008 from Lower Creta−
ceous seep carbonates of California. The shells from theOmagari site are higher spired than the latter species. The
most important shell character of Retiskenea is a protoconchwith reticulate pattern (Warén and Bouchet 2001). Unfortu−
nately the protoconch ornamentation is not preserved in anyof our specimens; therefore, we decided to leave this gastro−
pod unnamed—potentially it may represent an entirely dif−ferent group of gastropods—pending collection of better pre−served specimens.

KAIM ET AL.—SEEP GASTROPODS FROM CRETACEOUS OF HOKKAIDO, JAPAN

483

Fig. 13. Naticiform gastropod from the Campanian (Upper Cretaceous) Omagari seep site in Hokkaido, Japan. A. UMUT MM30189 in lateral (A1),latero−apical (A2), and apical (A3) views; A4, close up of the juvenile whorls, A5, close up of the initial whorl. B. UMUT MM30190 in lateral (B1), apertural(B2), and apical (B3) views. C. UMUT MM30191 in apertural (C1), lateral (C2), and apical (C3) views; C4, close up of the juvenile whorls in lateral view.
D. UMUT MM30192 in lateral (D1), apical (D2), and umbilical (D3) views.

Skeneiform gastropod
Fig. 14.

Material.—44 poorly preserved shells from the Omagari
site, all deposited at UMUT.
Dimensions.—The best preserved shell UMUT MM30193(Fig. 14A) is 2.2 mm high and 1.14 mm wide.
Description.—The shell is small and skeneiform with 3–3.5
inflated whorls and the suture deeply incised. Initial whorl
poorly preserved at all accessible specimens but apparently
orthostrophic. The teleoconch is smooth. The umbilicus iswide open with no sculpture on the basal area. The aperture isdrawn out peripherally and is cemented to the precedingwhorl in the parietal part.
Discussion.—The shells under consideration are of very sim−
ple morphology observed in a number of gastropod groups in−cluding small trochids, skeneids, neomphalids, and hetero−branchs. It seems that the initial whorl is orthostrophic andtherefore affinities to the heterobranchs are less likely thoughsome heterobranchs have the heterostrophy obscured. Amongvent and seep taxa a small trochid Helicrenion reticulatum
Warén and Bouchet, 1993 possesses very similar shell (Warén
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484

ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

Fig. 14. Skeneimorph gastropod from the Campanian (Upper Cretaceous) Omagari seep site in Hokkaido, Japan. A. UMUT MM30193 in apertural (A1),lateral (A2), and apical (A3) views. B. UMUT MM30194 in lateral (B1), apertural (B2), and umbilical (B3) views. C. UMUT MM30195 in apical view (C1)and close up of initial whorls (C2).

and Bouchet 1993; Desbruyères et al. 2006). The latter species
is characterized by large net−like pattern on its protoconch.
This character unfortunately is not preserved on our speci−
mens and that is why we decided to leave the species un−
named. Similar shells from Oligocene cold−seep carbonates of
Washington State have been classified by Kiel (2006) as thepeltospirid Depressigyra? sp. This identification, however, re−mains uncertain as the protoconch ornament could not be ob−served.

Gastropoda indet. 1
Fig. 12B.

Material.—A single incomplete shell from Omagari.
Dimensions.—The shell UMUT MM30186 (Fig. 12B) is
10.9 mm high and 5.82 mm wide.
Description.—The shell is elongated with 2.5 whorls pre−served. The whorls are weakly inflated and their surface issmooth. The suture is weakly incised. It remains unsure if
this lack of ornamentation is original character or resulted
from peeling off the outermost layer. The protoconch and ap−
erture characters are unknown.
Discussion.—The only strongly elongated gastropod in theseep localities under consideration is Hokkaidoconcha hiki−dai. However, the latter species occurs exclusively in Yasu−
kawa and its shell expansion is much weaker. The shell underconsideration may belong to a weakly preserved neogastro−
pod. Better preserved material is necessary to confirm this
supposition.

Gastropoda indet. 2
Fig. 12C.

Material.—A single incomplete shell from Yasukawa.
Dimensions.—The shell UMUT MM30187 (Fig. 12C) is

5.45 mm high and 4.62 mm wide (note that the shell is later−
ally compressed).
Description.—The shell is globose, low spired and it pos−sesses an enveloping last whorl. The shell surface is smooth.
The shell consists of two layers. Inner layer is cross−lamellar
while outer layer is fibrous prismatic.
Discussion.—The taxonomic position of this cassid−like shellremains unresolved pending additional better preserved mate−
rial.

Class incertae sedis
Family Gigantocapulidae Beu, 2007
Genus Gigantocapulus Hayami and Kanie, 1980
Type species: Helcion giganteus Schmidt, 1873; North Pacific region;
Campanian (Late Cretaceous); original designation.

Gigantocapulus sp.
Fig. 15.

Material.—Single juvenile shell from Yasukawa.
Dimensions.—The shell UMUT MM30196 (Fig. 15) is 4.4mm high, 5.9 mm long, and 4 mm wide.
Description.—The small shell is limpet−shaped with high el−evated apex. The apex is located anteriorly (or posteriorly de−pending on interpretation of the animal). The majority of theshell is ornamented by thick concentric undulations. The
shell becomes irregular in its anteriormost part displaying ir−
regular shell growth expressed by meandering undulations.
Aperture elliptical. Shell composed of three layers: outer−most layer very thin and most probably fibrous prismatic.
Medial layer also thin and crossed foliate recollecting irregu−
lar crossed foliate microstructure of Fuchigami and Sasaki(2005). The microstructure of the thick inner layer remains
unrecognized.

KAIM ET AL.—SEEP GASTROPODS FROM CRETACEOUS OF HOKKAIDO, JAPAN485

Fig. 15. A juvenile specimen (UMUT MM30196) of Gigantocapulus sp., a mollusk of uncertain taxonomic affinity in lateral (A, B), apical (C), and poste−rior (D) views. E. Cross section through the shell displaying three layers: an outer, possibly fibrous prismatic (fp), a middle cross foliate (cf), and an inner
layer of uncertain microstructure. F. Another section showing the same layers. G. Close up of the foliated structure, uppermost part of the layer consist ofpolygonal plates resembling broken semifoliated structure or detached tablets of nacreous structure.

Discussion.—The taxonomic position of Gigantocapulus has
been recently reviewed by Beu (2007), who stated that this ge−
nus may represent a tergomyan monoplacophoran, a vani−coroid gastropod, or a separate, extinct gastropod group. It isbeyond the scope of this paper to argue on high level classifi−
cation of this mollusk, however, the presence of crossed foli−
ated layer may suggest patellogastropod affinity.

Discussion
Historical background.—The Late Cretaceous record ofgastropods from chemosynthesis−based associations is sur−prisingly poor in comparison to the Early Cretaceous and Ce−
nozoic record. It is basically limited to two cold seep locali−ties in California and hydrothermal vent deposits Troodos
ophiolite, Cyprus. The Romero Creek (Upper Campanian)and Moreno Gulch (Santonian) seep deposits in California
yielded only two species of Hokkaidoconcha, a single spe−
cies in each locality (Kiel et al. 2008b). The Cypriot vent de−posits also revealed only hokkaidoconchid/provannid gas−
tropods (Little et al. 1999; Kaim et al. 2008a). This is in con−trast to Late Jurassic/Early Cretaceous seep localities whichhave abundant and diverse gastropod associations, for exam−ple in some sites in California (Campbell et al. 2008; Kiel etal. 2008b), the Crimea (Kiel and Peckman 2008), the Carpa−
thians (Ascher 1906), France (Macsotay 1980), and Antarc−
tica (Kaim and Kelly 2009). There is also relatively good Ce−
nozoic record of gastropods from chemosynthesis−based as−sociations (Moroni 1966; Marshall 1985, 1994; Goedert andSquires 1990; Taviani 1994; Squires 1995; Goedert andKaler 1996; Amano and Little 2005, Gill et al. 2005; Kiel
2006; Kiel and Goedert 2006a, b, 2007; Amano et al. 2007;
Kiel and Peckmann 2007). Therefore, the localities in
Hokkaido (especially Omagari and Yasukawa) yielding richand relatively well preserved Late Cretaceous hydrocarbon
seep gastropod associations fill the gap between Early Creta−
ceous and Eocene (Fig. 16). Surprisingly, the only taxa
which occur both in the Early and Late Cretaceous associa−
tions are hokkaidoconchids. They are common in numerous
DOI: 10.4202/app.2009.0042

Amberleya*
Paskentana
Hokkaidoconcha
Lithomphalus
Atresius
Retiskenea
Bathypupurinopsis
Desbruyeresia
Provanna
Bathyacmaea
Cantrainea
Cataegis
Homalopoma
Margarites
Serradonta

Age

ACTA PALAEONTOLOGICA POLONICA 54 (3), 2009

Genus

486

Plio-Pleistocene
Miocene?
Oligocene
EocenePaleocene
MaastrichtianCampanianSantonian
Coniancian
Turonian
Cenomanian
AlbianAptianBarremian
Hauterivian
Valanginian
Berriasian
Tithonian?

Fig. 16. List of gastropod genera and their stratigraphical ranges in Creta−
ceous chemosynthesis−based associations. The genera in bold occur in theCampanian (Late Cretaceous) hydrocarbon seep sites in Nakagawa area.
Note discrepancy in the composition of Lower and Upper Cretaceous gas−
tropod associations. *Similar to Amberleya is Bathybembix that is known
from chemosynthesis−based associations since Eocene and noted also intheir Recent counterparts (Kiel and Goedert 2006b; Kiel et al. 2008b).

localities in the Early Cretaceous (Kaim et al. 2008a; Kiel etal. 2008b) and also are present in two Late Cretaceous locali−ties in California (Kiel et al. 2008b). In Hokkaido they co−oc−
cur with provannids, which are allegedly their derivatives(Kaim et al. 2008a). Hokkaidoconchids may occur also in the
Eocene–Miocene of Barbados (Gill et al. 2005; Kaim et al.
2008a) and the Eocene of Washington State (Goedert andKaler 1996; Kaim et al. 2008a). These Cenozoic localities
constitute latest known occurrence of the group.
Faunal composition of the associations.—The seep sites at
Omagari and Yasukawa provided abundant and relatively di−verse gastropod associations. In sum we examined 1202
specimens from Omagari and 245 specimens from Yasu−
kawa representing 16 species (Table 2). The Omagari site is
the oldest−known hydrocarbon seep site with an ubiquity ofgastropod limpets, which are very common in Recent seepand vent communities. Serradonta omagariensis constitutes
36% of the gastropod association in Omagari. It is a rather
peculiar gastropod adapted for living on worm tubes which
occur in great numbers in this locality (Jenkins et al. 2007a).
Serradonta is an acmaeid gastropod restricted nowadays toseeps around Japan (Sasaki et al. 2005). The important com−ponent of both and Omagari and Yasukawa seeps are turbi−
nids. In Omagari they are represented by Homalopoma abe−shinaiensis and Cantrainea omagariensis which together
constitute 48% of the association. In Yasukawa turbinids are
represented only by Cantrainea yasukawensis, which consti−
tutes more than half (55%) of the association. Such an abun−dance of turbinids is rather surprising as such a compositionis unknown from ancient and Recent chemosynthesis−based
communities. Homalopoma has been reported from Recent
sunken wood (Okutani 2000) and occurs at a hot vent inMariana Arch (Anders Warén, personal communication2008) and has been identified in the Eocene hydrocarbon
seep deposits from Washington State (Goedert and Squires
1990) and Barbados (Gill et al. 2005); however, it never oc−
curs in such a density. Only Moroni (1966), who described
Homalopoma domeniconii Moroni, 1966 from the Miocene“Calcare a Lucine”, noted that in some localities this species
is very common. Cantrainea is also a rather uncommon
taxon in Recent chemosynthesis−based associations. There
are three species of this genus living in Recent cold seep on
the Louisiana Slope (Warén and Bouchet 1993), in Chile(Sellanes et al. 2008), and at hydrothermal vent off Japan(Okutani and Fujikura 1990) respectively, but again they are
rather uncommon at these sites. Of special interest is a spe−
cies described by Okutani (2001) seemingly from a hydro−
thermal vent in the Okinawa Trough as Cantrainea nuda as it
closely resembles the species of Cantrainea from Omagari
and Yasukawa. C. nuda is based on a single shell and the spe−
cies has not been collected alive since its first discovery, sug−gesting that it is a rather uncommon species. Gill et al. (2005)
reported presence of Cantrainea sp. in seep carbonate of the
Miocene Freeman’s Bay Limestone, Trinidad. The trochid
Margarites sasakii reaches moderately high number of spec−
imens contributing 3% to the entire association at the Oma−gari site. A similar species is known from vents in the Oki−nawa Trough (Sasaki et al. 2005). The hokkaidoconchid
Hokkaidoconcha is present only in the much lower flux
Yasukawa site where it occurs abundantly constituting 39%of the association, while it is absent in the much higher flux
Omagari seepage, where it possibly is replaced by Provanna(6.2% of the gastropod association). Neomphalids have notbeen found at the Omagari and Yasukawa sites although thenaticiform gastropod might represent a species of Retiske−nea. This assumption, however, cannot be validated based on
the available material.
Comparison of Omagari and Yasukawa associations.—
The two localities under consideration are geographicallyvery close each other and apparently also stratigraphically.
The most conspicuous difference between the two sites is insize of the seep carbonates. The carbonate body at the Oma−gari site reaches 5 m in height, whereas the Yasukawa site
consists of a series of smaller carbonate bodies, the largest ofwhich is only 1 m high. Jenkins (2007b) argued that this dif−ference apparently reflects the longevity of the hydrocarbon

KAIM ET AL.—SEEP GASTROPODS FROM CRETACEOUS OF HOKKAIDO, JAPAN

seep and/or the flux. This difference most probably influ−
enced the associations’ composition. Jenkins et al. (2007a)
described a positive relationship between the presence ofworm tubes and Serradonta limpets in Omagari and Yasu−
kawa. At the Omagari site, where plenty of worm tubes arepresent, Serradonta limpets are very common. At the Yasu−
kawa site worm tubes are rather uncommon, coincident with
low number of Serradonta specimens. Interesting is that
Provanna nakagawensis occurs at both sites (although much
more commonly at the Omagari site), while Hokkaidoconcha
hikidai occurs exclusively at the Yasukawa site. It might be
hypothesized that H. hikidai could not tolerate higher con−centrations of methane and/or sulfide in Omagari. Also theabsence of Homalopoma from the Yasukawa site is difficult
to explain, especially because Cantrainea (another turbinid)
is abundant at both localities even though there are two dif−ferent species of Cantrainea present in each of the sites.
Noteworthy is also the absence of the naticiform gastropod
and the skeneiform gastropod from the Yasukawa site. Theirabundance at the Omagari site suggests that they were typicalanimals at hydrocarbon seep communities (unless Omagari
seep carbonate recorded unusual community). The numberof species at the Omagari and Yasukawa sites is almost equal(10 and 9 respectively) but it is noteworthy that five species
make 93% of all gastropods at Omagari, while only two spe−
cies constitute 93% of all gastropod specimens at Yasukawa(Table 2).
Other Cretaceous chemosynthesis−based associations in
Hokkaido.—Gastropods from other hydrocarbon seep car−bonates in Japan are poorly known. Gastropods are relatively
common in the Cenomanian seep carbonate at Kanajirisawa(Kaim et al. 2008a) and the Albian seep carbonate at Utagoe(AK and RGJ unpublished data), and in both cases they are
dominated by hokkaidoconchids and provannid−like species.
The Albian Pombetsu seep has not revealed any good gastro−
pod material. The Gakkonosawa seep provided only a few
gastropod specimens, mostly provannids (Kaim et al. 2008a;
AK and RGJ unpublished data). Kaim et al. (2008b) de−
scribed two chemosynthesis−based associations from Turo−nian and Coniacian plesiosaur falls reporting numerous spec−
imens of provannids and a vetigastropod very similar to
Cantrainea omagariensis. Kiel et al. (2008) described two
Campanian sunken wood associations from the Nakagawa
area. One of these, the Akita Creek wood fall, contained also
some gastropods including two possible provannids, twoskeneimorphs, and a limpet. At least one of the provannids(Kiel et al. 2009: fig. 3E) is similar to Provanna naka−
gawensis from the Omagari and Yasukawa seep sites while
the skeneimorphs recall Cantrainea omagariensis. Only the
Akita wood fall limpet seems to have no seep counterparts in
the Cretaceous of Hokkaido. Moreover, a single specimen ofthat limpet has recently been found associated with a piece ofwood from the Yasukawa River (Steffen Kiel, personal com−munication 2009). The new finding may suggest that thislimpet might be an important and distinct member of the lo−

487

cal wood−fall fauna. Otherwise it seems that the gastropod
composition of the chemosynthesis−based associations was
relatively uniform in hydrocarbon seeps, plesiosaur falls, andsunken wood. The most important gastropod groups in such
communities were provannids/hokkaidoconchids, turbinids(especially species of Cantrainea), and, at least in hydrocar−
bon seeps, acmaeid limpets. This suggests that these commu−
nities might not yet differentiated into three different types as
it has been observed for their Recent counterparts. This pat−tern seems to be neutral to the hypothesis of evolutionary anddispersal stepping stones between particular types of chemo−
synthesis−based associations (Smith et al. 1989; Martill et al.
1991; Distel et al. 2000) as apparently the species could mi−
grate from every type of the community to another type in the
Cretaceous of Hokkaido. The impoverished taxonomic com−position of plesiosaur bone− and wood−fall associations may
suggest that they document “incipient” or opportunistic colo−
nization of a sulfide−rich substrate from adjacent hydrocar−
bon seeps (Kaim 2008a; Kiel et al. 2009).

Conclusions
The Omagari and Yasukawa seep sites revealed the mostplentiful and most diversified gastropod associations from
Late Cretaceous chemosynthesis−based communities. They
fill the gap between the recently documented (Campbell et al.
2008; Kiel et al. 2008) gastropod associations from the Early
Cretaceous and their much better investigated post−Creta−
ceous counterparts. The gastropods from the Omagari and
Yasukawa seep sites are much more similar to post−Creta−
ceous seep faunas than to their Early Cretaceous counter−parts. The only group that connects Late Jurassic/Early Cre−taceous and Late Cretaceous associations are the hokkaido−
conchids (Kaim et al. 2008a, b; Kaim and Kelly 2009). The
remaining groups display a remarkable similarity to their Re−
cent counterparts from the vicinity of the Japanese islands
and the Western Pacific in general. This suggests that there
was a regional pool of animals that flourished in chemo−
synthesis−based communities since the Late Cretaceous until
today. The similarities among gastropod associations (butalso bivalve associations, see Kiel et al. 2008a, b; also AK
and RGJ unpublished data) in Late Cretaceous hydrocarbon
seeps, vertebrate falls, and wood falls strongly suggests thatthese faunas were not yet differentiated into three distinctive
types of communities.

Acknowledgements
Kazushige Tanabe (DEPUT) is heartily acknowledged for his support
on all stages of this research. AK’s comparative studies on Recent gas−
tropods from chemosynthesis−based communities in Naturhistoriska
Riksmuseet, Stockholm, Sweden were possible due to SYNTHESYSSE−TAF (the European Union−funded Integrated Infrastructure Initia−
tive grant) under a kind supervision of Anders Warén who is also ac−
DOI: 10.4202/app.2009.0042

488
knowledged for sharing with us his enormous knowledge on gastropods
from chemosynthesis based communities. Takenori Sasaki (UMUT)
helped in various ways during the preparation of this paper. Hiroshi
Saito (NSMT) is thanked for the photographs of Cantrainea nuda.
Masako Hara (ORI) is also thanked for her help in operating SEM at
ORI. Takenori Sasaki and Anders Warén are thanked for their com−ments on an early draft of this paper. The comments from anonymousreferee and Steffen Kiel (University of Kiel, Germany) are highly ap−
preciated. The research of AK was supported by the Japan Society for
the Promotion of Science (JSPS) Postdoctoral Fellowship for Foreign
Researchers and associated research grant number 17.05324 (project
number 050500000614). The research of RGJ was supported by the
Nippon Foundation−HADal Environmental Science Education Pro−
gram (HADEEP). AK and RGJ were also supported by JSPS grant no.
18403013 (leader Kazushige Tanabe).

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