PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 114(1):172-177. 2001. A new fossil geryonid crab (Crustacea: Decapoda: Brachyura) from the late Pliocene to early Pleistocene of Japan Hisayoshi Kato and Akihiro Koizumi (HK) Natural History Museum and Institute, Chiba, 955-2, Aoba-cho, Chiba 260-8682, Japan; (AK) lida City Museum, 2-655-7, Ote-machi, lida 395-0034, Japan — Abstract. A new fossil geryonid crab, Chaceon matsushimai is described from the uppermost Pliocene to lower Pleistocene Ofuna and Koshiba forma- tions, Kazusa Group in Kamakura and Yokohama cities, central Japan. The new species resembles members of the extant Chaceon granulatus species group, but is distinguished by having very faint frontal, second, and fourth anterolateral spines and a proportionately narrower male abdomen. This is the first fossil record of the genus Chaceon from Japan. Recent revisions of deep sea geryonid assignable to the same species (here re- & crabs (Manning Holthuis 1987, 1989) ferred to as the Koshiba specimens). previously placed in the genus Geryon In addition, a fossil specimen in the col- Kr0yer, 1837, have shown that species lection by late Professor Rikizo Imaizumi which possess five anterolateral spines on preserved in the Institute of Geology and the carapace and four distinct spines on the Paleontology, Tohoku University, is also frontal margin should be referred to the ge- identical to the present new species (here nus Chaceon (Manning & Holthuis, 1989). referred to as the IGPS specimen). Al- Species of Geryon [type species: Geryon though this specimen lacks a label and in- trispinosus (Herbst, 1803)] have only three formation about the locality, stratigraphic anterolateral spines, and less pronounced horizon and name of collector, a piece of frontal spines. Based on these carapace fea- card belonging to the specimen and proba- tures, the new species of fossil described bly written by Imaizumi reads "Kamaku- herein is referable to Chaceon, which has ra". The matrix of this specimen is indis- eight living species in the Pacific Ocean, tinguishable from those of the Ofuna spec- two of which are found in Japanese waters imens. & (Ng Manning 1998). The Ofuna specimens occurred in mas- & Koizumi Matsushima (1992) first re- sive, light gray-colored siltstone exposed in ported fossils of Geryon species in associ- the land-development field for residential ation with molluscs and fishes indicative of construction in Iwase, Kamakura City, Kana- lower sublittoral to upper bathyal waters gawa Prefecture, central Japan (35°20'58"N, from the lower Pleistocene Ofuna Forma- 139°32'51"E). The crab-bearing horizon is tion, Kazusa Group in Kamakura City (re- stratigraphically situated between the Ny ferred to here as the Ofuna specimens). Tuff Bed (Nakaya Tuff bed: same as 026 & Poorly preserved cyclodorippid crab Ty- (Of2) in Mitsunashi Kikuchi, 1982) and molus species were also obtained from the the Is Tuffbed. The former is a remarkable locality. As noted by these authors, two key bed widely traceable in the Yokohama- specimens deposited in the Kanagawa Pre- Kamakura area. fectural Museum of Natural History, which The Koshiba specimens had been ob- had been collected by Mr. Syozo Aizawa tained from the massive, light gray-colored from the overlying Koshiba Formation, are pumiceous sandy siltstone of the lower part VOLUME 114, NUMBER 1 173 of the Koshiba Formation exposed in the IGPS coll. cat. no. 103703 (paratype 1; cw land-development field in the Seibu-danchi, 59.0 mm, cl —51.5 mm). Nishishiba, Kanazawa-ku, Yokohama City Diagnosis. Small Chaceon with 4 faint (35°21'N, 139°38'E). They are mostly im- projections on frontal margin, and 3 distinct pressions and/or molds due to compression spines and 2 very faint spines or lobes on and weathering. anterolateral margin. Male abdomen rela- & Mitsunashi Kikuchi (1982) correlated tively narrow. — several remarkable tuff beds in the Ofuna Description. Carapace hexagonal in Formation with those in the lower Pleisto- outline, broader than long. Frontal margin cene Otadai and Kiwada formations of the about 0.25 of maximum width with 2 very Boso Peninsula. Eto et al. (1987) consid- low medial and 2 lateral lobes. Orbit large; ered the age of the Ofuna Formation to be relatively shallow; margin rounded. Antero- early Pleistocene based on the planktonic lateral margin convex with first, third, and foraminifera (N22 Zone ofBlow 1969) and fifth spines distinct and second and fourth calcareous nannoplankton ("CN12" Zone present as very low spines or lobes. First of Okada and Bukry 1980). However, the spine (outer orbital) directed obliquely an- calcareous nannoplankton assemblage of teriorly. Second minute spine observed in the formation identified by them indicates smaller specimen (paratype 2: Figs. 1, 4a), that the age extends into the latest Pliocene being indistinct lobe in largest specimen (CNlBa Zone of Okada & Bukry 1980: Y. (paratype 1: Figs. 2, 4c). Third spine point- Tanaka pers. comm.). Considering these ed with broad base. Fourth spine very low facts, the geologic age of the fossils from with blunt tip. Fifth spine triangular, largest, the Ofuna and Koshiba formations is most directed laterally. Distance from first to likely to be latest Pliocene to earliest Pleis- third spines slightly shorter than that from tocene (ca. 1.9-1.7 Ma). third to fifth. Dorsal surface moderately The specimens are deposited in the Ka- convex; rugose, granulated in posteriorhalf nagawa Museum ofNatural History (KPM- oflarge specimen (Figs. 2, 3). Branchial re- NN) and Institute of Geology and Paleon- gion sparsely granulated. Sparse granules tology, Faculty of Science, Tohoku Univer- on protogastric, mesogastric, and cardiac sity (IGPS coll. cat. no.). The abbreviations regions. Regions divided by shallow de- cl and cw indicate carapace length and car- pressions. Weakly developed transverse apace width. ridge extends from branchiocardiac groove to fifth anterolateral spine. In smallest spec- imen (KPM-NN-5942), however, dorsal re- Family Geryonidae Colosi, 1923 gions well divided by deep grooves; proto- Genus Chaceon Manning & Holthuis, , meso- and metagastric, cardiac and bran- 1989 chial regions convex; an arched convex, Chaceon matsushimai, new species well demarcated ridge extends from bran- Figs. 1-4 chiocardiac groove to fifth anterolateral spines. Frontal and anterolateral spines of Geryon sp.: Koizumi & Matsushima, 1992, carapace proportionally larger than in other p. 127, figs. 8-1-3. larger specimens. — Male abdomen relatively narrow; fourth Material examined. KPM-NN-5941 segment slightly shorter than fifth; lateral (holotype; cw 66.0-1- nam, ca. 70 mm, cl margins of fifth segment almost parallel; 55.9 mm), 5942 (cw 15.5+ mm, cl 15.8 telson triangular. mm), 5943 (paratype 2; cw 32.5 rrmi, cl Chelipeds nearly equal in size. Upper 24.4 mm), 198A (cw 31.4 mm, cl 28.3 surface ofmerus with small subdistal spine; mm), 198B (cw 49+ mm, cl 44+ mm). carpus with strong inner distal spine. Palm 174 PROCEEDINGS OFTHE BIOLOGICAL SOCIETY OF WASHINGTON Figs. 1-3. Chaceon matsushimai. new species. 1, Paratype 2, KPM-NN-5943, carapace. XI.Oi 2, Paratype 1, IGPS coll. cat. no. 103703, Xl.O, 2a, thoracic sternites and abdominal somites, 2b, carapace and cheliped: 3, Holotype, KPM-NN-5941, 3a, leftcheliped, ventralview, X0.7, 3b, leftcheliped,pereiopodsandcarapace, x1.0. VOLUME 114, NUMBER 1 175 tioned living species (see Ng & Manning 1998). The present new species also resem- bles Chaceon bicolor Manning & Holthuis, 1989, from the North and South Pacific Ocean in having lobiform second and fourth anterolateral spines, but is distin- guished from that extant species by having dorsoventrally flattened dactyli of ambula- tory legs and exhibiting less developed frontal spines. The general outline ofthe carapace ofthe new species resembles those of the genus Fig. 4. Chaceon matsushimai, new species. Front- Geryon Kr0yer, 1837, in appearance, i.e., orbital and anterolateral margins, a, paratype 2; b, ho- frontal spines are very low and the antero- lotype; c, paratype 1. Scales: 1 cm. lateral margin has very faint second and fourth spines which are sometimes undis- sparsely granulated on outer and upper sur- cemible, instead of five distinct spines. Al- faces. Both fingers with strongly serrated though the second spine of the left antero- occlusal margins; longitudinal furrow and lateral margin is entirely undiscemible in row of pits present on outer surface. the holotype specimen (Figs. 3, 4b), minute Ambulatory legs long; dactyli dorsoven- spines or convexities are observed in para- trally compressed, slightly curved down- types 1 and 2 (Figs. 4a, c). ward. — The length/width ratio of the merus of Etymology. In honor of Dr Yoshiaki the fifth ambulatory leg of the holotype Matsushima of the Kanagawa Prefectural specimen is 4.3. Due to compression after Museum of Natural History who has made burial, unfortunately, this value is by no great contributions to the geology and pa- means reliable. leontology of the Kanto region as well as The only known other fossil species of to Quaternary molluscan paleontology and the genus is Chaceon peruvianas paleoecology. (d'Orbigny, 1842) from the middle Eocene — Remarks. Thepresentnew species most of Argentina, which was recently trans- closely resembles members of the living ferred from the extinct genus Archaeoger- & Chaceon granulatus species group, viz. C. yon Colosi, 1923 (Schweitzer Feldmann granulatus (Sakai, 1978), C. manningi Ng 2000). et al., 1994, C. A;arMterManning, 1993, and The fossil species of the genus Geryon C. micronesicus Ng & Manning, 1998, in had hitherto been restricted to the Miocene having granulose branchial region, very to Pliocene of Europe-Tethys region (see low second and fourth anterolateral spines, Dawson & Webber 1991). Other records of and dorsoventrally flattened dactyli of am- fossil Geryonidae are the extinct generaAr- bulatory legs. In addition to the small adult chaeogeryon Colosi, 1923, Coeloma A. size, however, Chaceon matsushimai is eas- Milne-Edwards, 1865 and Archaeoplax ily distinguished from these living species Stimpson, 1863 (Glaessner \969).Archaeo- by having very faintly projected frontal geryon was known from the Miocene of spines, relatively weaker second and fourth South America (Glaessner 1969, Morris, anterolateral spines, a broader and shallow- 1980; the geologic age may have to be re- er orbit and a less granulated carapace. assigned, see Schweitzer & Feldmann Moreover, the male abdomen, especiallythe 2000). Archaeoplax has been reported from fourth and fifth segments, are proportion- the Miocene of North America (Rathbun ately narrower than those of above men- 1935). Although Coeloma has been report- 176 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON ed from the Eocene to Oligocene rocks of ciety of America and University of Kansas Europe and North America, the placement Press, Lawrence. within the Geryonidae is still uncertain be- Herbst,chJi.cFhteW.der17K9r9a-b1b8e0n4.KrVeebrsseuchnebesitnereinNeartusrygsetse-- cause it differs considerably from the living matischen Beschreibung ihrer verschiedenen species ofGeryonidae in morphology ofthe Arten. 1-3:515 pp., 62 pis., G. A. Lange,Berlin dorsal carapace (Schweitzer & Feldmann & Stralsund. 2000). Koizumi, A., & Y. Matsushima. 1992. Upper bathyal molluscanfossils, Crustaceaandfishesfromthe Acknowledgments Lower Pleistocene Ofu—na Formation in Kama- kura, southern Kanto. Natural history report The authors are much indebted to Pro- of Kanagawa (Kanagawa Prefectural Museum) fessor Peter K. L. Ng, National University 13:119-128. (in Japanese) — Kr0yer, H. 1837. Geryon tridens, en ny Krabbe. Na- of Singapore, for his criticisms ofthe man- turhistoriskTidsskrift 1:10-21, pi. 1. uscript and many instructive comments. We Manning, R. B. 1993. A new deep-sea crab, genus are grateful to Mr. Hajime Taru and Mr. Chaceon, from I—ndonesia (Crustacea: Decapo- Takehiro Sato, Kanagawa Prefectural Mu- da: Geryonidae). Raffles Bulletin ofZoology osteou,mToofhoNkatuurUanlivHeirsstiotryy,;faorndthMeri.r aJsusnisNteanmc-e Manning4G,1e(r2Ry.)o:nB1.6,t9r-&i1s7pL2i..noBs.usHo(lHtehrubisst.)1(98G7e.ryoTnhiedaSet)a.t—usIonf- in the examination offossil and Recent ma- vestigacion Pesquera 51 (Supplement 1): 57-62. terials. We thank Dr. Yuichro Tanaka, Geo- , & . 1989. Two new genera and nine logical Survey of Japan, for giving com- new species of geryon—id crabs (Crustacea, De- ments concerning the geologic age of the capoda, Geryonidae). Proceedings of the Bi- ological Society ofWashington 102:50-77. formations. Thanks are also due to Dr. To- Mitsunashi, T, & T. Kikuchi. 1982. Geology of the moyuki Komai, Natural History Museum Yokohama district. Quadrangle Series, Scale 1: and Institute, Chiba for valuable comments 50,000, 105 p. Geological Survey ofJapan, (in concerning the systematic position of the Japanese with English abstract, 4 p.) Milne-Edwards, A. 1865. Monographic des crustaces fossil crabs. — delafamillecanceriens. AnnalesdesSciences Naturelles, Sen 4, Zoologie. 3:297-351, pi. 5- Literature cited 13. Blow, W. H. 1969. Late Middle Eocene to Recent Morris, S. F 1980. Catalogue ofthe type and figured specimensoffossil Crustacea(excl. Ostracoda), planktonic foraminiferal biostratigraphy. in P. Bronnimann and H. H. Renz, eds.. Proceedings Chelicerata, Myriapoda and Pycnogonidainthe ofthe First International Conference on Plank- British Museum (Natural History). British Mu- tEo.niJ.cBMriilclr,ofLoesisdielns., Geneva, 1967. 1:199-421, Ng, P sKe.umL.,(N&atuRr.alB.HisMtaonrnyi),ng5.3 1p9.98. A new deep- Colosi,caGp.od1i923br.acUhniuaris)p.e—ciBeolfeoststiilneoddielGleariSoonciideeta(Ddee-i wtoattehrecPraacbiffircomspeBceileasu,ofMiCchraonceesoina—(wCirtuhstaackeeay: Decapoda: Brachyura: Geryonidae). Proceed- Naturalisti in Napoli, 35 (Sen 2, vol. 15), 37: 248-255. ings of the Biological Society of Washington Dawsonr,edE.crWa.b,C&haWc.eoRn. (W"eGbebreyro.n"1)9.91—.NTahteiodneaelp-Msue-a 1,1D1.:-3A8.9-L3e9e7,.& H.-R Yu. 1994. A new deep sea seumofNew Zealand, MiscellaneousSeries24, crab ofthe genus Chaceon (Decap—oda, Geryon- 83 pp. idae) from the South China Sea. Cru.staceana Eto, T, M. Oda, S. Hasegawa, N. Honda, & M. Fu- 67:371-380. nayama. 1987. Geologic age and paleoenviron- Okada, H., and Bukry, T 1980. Supplementary mod- ment based upon microfossils of the Cenozoic ification and introduction of code numbers to sequence inthe mi—ddleandnorthernpartsofthe the low-latitude coccolith b—iostiatigraphic zo- Miura Peninsula. 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Geological Society of sil Portunid from Washington, USA, and Ar- America Special Papers 2, 160 p., 2 figs., 26 gentinaandareevaluationofgenericandfamily pis.