VENUS 63 (3-4): 87-94, 2005

Four Protobranch Bivalves Collected by the ROV Kaiko from Hadal Depths in the Japan Trench

Takashi Takashi Okutani and Yoshihiro F吋iwara Japan Agency 舟r Marine-Earth Science and Technology (JAMSTEC), 2-15 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan; [email protected] ・.jp

Abstract: Abstract: Four protobranchiate bivalves were collected by the ROV Kaiko from hadal depths in in the Japan Trench in July 2002. They are Katadesmia vincula, Neilonella pn ゆ nda n. sp., Ledellina Ledellina convexirostra and Yoldiella kaikonis n. sp.

Keywords: Keywords: , Japan Trench, new species, ROV Kaiko

Introduction Introduction

The ROV Kaiko with the support ship R 八F Kairei made s巴veral dives into abyssal and hadal depths depths on both the landward and seaward slopes of the Japan Trench in July 2002. Among the bottom bottom sediment scooped up for the pu 叩ose of biological and geophysico-chemical surveys, more than than a dozen of sp 巴cimens of small protobranchiate bivalves were found. They are classified into four four species including two new ones.

Source of material

The specimens examined for the present study were collected from the following dives of the ROV Kaiko (Fig. 1):

Dive Dive 252 (July 13, 2002) 40°02.73 ’ N, 144°16.48' E: 7299 m. Dive Dive 253 (July 14, 2002) 40°02.77 ’ N, 144°16.44' E: 7321 m. Dive Dive 255 (July 21, 2002) 40°02.85 ’ N, 144°16.61' E: 7333 m. Dive Dive 258 (July 24, 2002) 39°06.66' N, 143°53.25 ’ E: 5225 m. Dive Dive 259 (July 25, 2002) 40°02.75' N, 144°16.31 ’ E: 7320 m.

The specimens were all extracted on board the R 八F Kairei from sediment samples collected by the the scoop-sampler manipulated by the ROV Kaiko.

Abbreviations Abbreviations used in the present paper: JAMSTEC Japan Agency for Marine-Earth Science Science and Technology; NSMT - National Science Museum, Tokyo; SL - Shell length; SH - Shell Shell height; SW - Shell width; UMUT University Museum, the University of Tokyo. 88 88 T. Okutani & Y. F吋iwara

43 N

42 N

41 41 N

40 N

39 N

37 N 140 E 141 E 142 E 143 E 144 E 145 E

Fig. Fig. 1. Positive stations (Kairei!Kaiko diving stations in July 2002) for the present specimens.

Taxonomy

F創凶ly Malletiidae H. Adams & A .Adams , 1858

Katadesmia Katadesmia vincula (Dall, 1908) (Fig. (Fig. 2A, B)

Mate1 旬l examined: Two specimens from Dive 259 (7320 m). Remarks: Both specimens are small and young (SL 4.4 mm and 7.5 mm). This species was frequently frequently treated to be conspecific with the Atlantic Katadesmia cuneata (Jaffreys , 1876) by some early authors (e.g. Knudsen, 1970) and cited as a cosmopolitan species with bathymetrical range range of 2400-6200 m. Occurrences of 出is species from the waters neighboring the Japanese Islands Islands were also reported under the name Mallettia cuneata by Okutani (1975) and Okutani Four Four Protobranch Bivalves in th 巴 Japan Trench 89

Fig. Fig. 2. Four protobranch species. A, B. Katadesmya vincula from Dive 259. C, D. Neilonella profunda n. sp. sp. from Dive 258 (holotyp 巴） . E, F. Ledellina convexirostris from Dive 258 . G, H. Yoldiell α kaikonis n. sp. sp. from Dive 252 (holotype). 90 90 T. Okutani & Y. F吋iwara

& Kawamura (2002) from the depths between 5440 m and 6210 m. Belyaev (1989) listed the same name from a depth of 6156-6207 m in the Japan Trench. Coan et al. (2000) accepted the the separation of the Atlantic K. cuneat αfrom， the Pacific K. vincula, as the latter has a more posteriorly posteriorly elongated shell. Knudsen (1970) and Coan et al. (2000) considered that Malletia flora flora Dall, 1916, from 2869 m o 妊 Alaska is a synonym. Coan et al. (2000) gave 590-3585 m for the the depth range of this species, probably in the East Pacific. The pr 回 ent record may represent a bathymetrical bathymetrical extension of about 1000 m over the previous records in the Northwest Pacific.

Family Family Schileyko, Neilonellidae 1989

Neilonella Neilonella projunda n. sp. (Fig. (Fig. 2C, D)

Mate1 抱 l examined: Two sp 配 imens from Dive 258 (5225m) and a single specimen from Dive 259 (7320 m). Des ct かtion: Shell small, thin, translucent, equivalve, inequilateral. Shell surface glossy, covered covered with pale yellowish periostracum, ornamented by crowded, very delicate, rather regularly spaced, spaced, commarginal threads. Umbo situated nearly centrally (at about 539 もanteriorly), low, almost almost orthogyrous. Antero-dorsal margin gently slanting, continuing to rounded frontal margin, then then to smoothly convex ventral margin; posterior tip rather acute; postero ・dorsal m 紅 gin gently ascending. ascending. Ligament weak, opisthodetic. Interior surface glossy. Hinge plate weak with very short, short, rectangular, edentulous space between anterior and posterior arcs. Anterior arc carrying 10 taxodont taxodont tee 出， posterior arc 12 which are diminishing size towards center. Pallial sinus shallow. Soft Soft parts not examined. Measurements: Measurements: SL SH SW Holotype Holotype (UMUT-RM 28901) 6.7 mm 4.3 mm 2.4 mm (Dive 258: Fig. 2C, D) Paratype Paratype #1 (NSMT 4.7 mm 3.2 mm 1.8 mm (Dive 259) Paratype Paratype #2 (NSMT-Mo 73628) 5.7 mm 3.6 mm -- (Dive 258: RV fractured)

Remarks: The present species has a rather thin shell for 出e genus. The commarginal sculpture is is much more delicate than but similar to those of some members of both Ledella Verrill & Bush, 1897, 1897, and Tindaria Bellardi, 1875. However, the pr 田 ent species has no posterior sulcus, unlike Ledella, Ledella, and is separable from Tindaria by its orthogyrous umbo, discontinuous arcs of hinge teeth teeth and opisthodetic ligament. Austrotindaria Fleming, 1948, lacks an edentulous space between ant 巴rior and posterior 紅白 of hinge teeth, and has an amphidetic ligament. Among abyssal- hadal hadal protobranchs from the neighboring waters, the present species is comparable to Neilonella abyssopacifica abyssopacifica Okutani & Kawamura, 2002, from a depth of 5660 m in the Northwest Pacific Basin, Basin, east off the Izu Islands. However, the present new species has longer anterior portion, a much thinner shell ornamented by distinct commarginal threads, and a larger number of hinge teeth. teeth. E 砂mology: The speci 回 name is derived from the Latin pr. φmdum, meaning “deep ”． Four Four Protobranch Bivalves in the Japan Trench 91

Family Family Nuculanidae H. Adams & A. Adams, 1858 Subfamily Subfamily Ledellinae Allen & Sanders, 1982

Ledellina Ledellina convexirostra Filatova & Schileyko, 1984 (Fig. (Fig. 2E, F)

Material Material examined: A single specimen from Dive 258 (5225 m). Remarks: The sole specimen in the present study measured 4.4 mm SL, 2.8 mm SH. The type type locality of this species is Vityaz St. 5620, 44°48' N, 156°33 ’ E, in the Kurile- Kamtchatka Trench, Trench, at a depth of 5030-5070 m (Filatova & Schileyko, 1984). Besides the type locality, they also also collected this species 企om the Japan Trench, 6608 m （切り 1az St. 6152). Coan et al. (2000) reported reported this species from the northeastern Pacific, from the Alaska Peninsula to off Oregon, at depths depths between 2800 and 6608 m.

Subfamily Subfamily Yoldiellinae Allen & Hannah, 1986

Yoldiella Yoldiella kaikonis n. sp. (Figs. (Figs. 2G, H; 3A-C)

Material Material examined: Six specimens from Dive 252 (7299 m); a single specimen from Dive 253 (7321 (7321 m); 10 specimens from Dive 255 (7333 m); 7 specimens from Dive 259 (7320 m). Description: Description: Shell minute, rather solid, inflated (SW/SL> 0.5) equivalve, slightly inequilateral (Fig. (Fig. 2G, H). Surface glossy, covered by pale olive-colored periostracum; smooth at a glance, but but ornamented by very crowded, slender, commarginal threads, that are crossed by crowded, microscopic, microscopic, discontinuous, radiating lines (Fig. 3B). Umbo well inflated with slightly opisthogyrous opisthogyrous beak, situated at about 56% anteriorly. Profile nearly oval (SH/SL = ca. 0.75), with with roundly curved anterior margin, smoothly convex ventral margin, and very slightly narrowed ’ posterior posterior margin. Interior surface porcellaneous white, rather dull. Hinge plate strong, ca 訂 ying about about 12-14 teeth on anterior arc and 9-10 teeth on posterior arc. Small, triangular resilifer accommodates large, quadrangular resilium (Fig. 3A). Ligament short, amphidetic. No lunule, nor escutcheon escutcheon delineated.

posterior posterior adductor adductor muscle muscle anterior anterior adductor adductor muscle muscle siphon siphon

foot foot palp

Fig. Fig. 3. Yoldiella kaikonis n. sp. A. Large resilifer intact on a fresh specimen. B. A part of 巴xternal sculpture ，巴 nlarged. C. Gross observation on soft part. 92 92 T. Okutani & Y. F吋iwara

Gross Gross observation on soft part revealed that the intestine forms a single loop on the right side (Fig. (Fig. 3C). Siphonal tentacle is indistinct. Measurements (in mm): SL SH SW Holotype Holotype (UMUT-R 28902) 6.6 4.8 3.5 (Dive 252: Fig. 2G, H) Paratype Paratype #1 (NSMT-Mo 73629) 6.5 4.9 3.4 (Dive 253) Paratype Paratype #2 (NSM 下Mo 73630) 6.4 4.6 3.4 (Dive 252) Paratype Paratype #3 (NSM 下 Mo 73631) 6.3 4.6 3.6 (Dive 253) Paratype Paratype #4 (NSM 下Mo 73632) 6.3 4.7 3.3 (Dive 252) Other Other specimens are preserved in JAMSTEC. Remarks: This species is characterized by its oval outline, inflated shell, its large resilium on a reduced resilifer, and the single loop of the intestine. Even though the general appearance of this this species recalls Tindaria, the possession of a poor but distinct resilium separates it. According to to the original definition by Verrill & Bush (1897), YoldieU αhas a resilifer. Schileyko (1985) claimed claimed that Yoldiella (s.l.) contains Portlandia, which has an apparent chondrophore. Allen & Hannah (1986) redefined Yoldiella as lacking a chondrophore, and Ockelman & W 紅白（1998) demonstrated demonstrated the poor definition of the resilifer in Yoldiella. Coan et al. (2000) also depicted Yoldiella Yoldiella with a resilifer. The present taxon has a distinct resilium on a weak resilifer, which fits Yoldiella Yoldiella (s.s.) as defined by Schileyko (1985), Waren (1989), and Allen et al. (1995).

The present species is comp 紅 able to Y. hoylei (Smith, 1885) from the mid-North Pacific, 2900 fathoms (Challenger St. 244), but Smith ’s species is less inflated (SW/SL = ca. 0.45) and has has a smaller number (six) of teeth on each arc of the hinge plate. Moreover, growth lines do not develop develop into commarginal riblets in Y. hoylei (Okutani, 1976). Y. sp. A of Coan et al., 2000 from Tufts Tufts Abyssal Plain off Oregon at 4882 m, bears a certain similarity to the present new species in its its oval profile, but it is thin-shelled, with smaller and fewer (eight) hinge teeth. E 砂mology: The species name comes from the Japanese "kaiko ”meaning marine trench, which which was adopted for the name of the ROV Kaiko as well.

Discussion Discussion

In In contrast to the dense and patchy distribution patterns of vesicomyid clams (Calyptogena phaseoliformis phaseoliformis and C. fossajaponica) and thyasirids (Axinulus had αlis), the minute protobranchs in in the present study were broadly scattered in the sediment samples. The pr ，回 ent specimens were all discovered in the sediment scooped by the ROV Kaiko for the the purpose of collecting above-mentioned chemosynthetic bivalves. They do not seem confined to to chemosynthetic-based communities, but ra 出 er to be vagrants incidentally scooped with the environmental environmental sediments. No protobranchs have hitherto been known to be associated with a chemosynthetic chemosynthetic environment, but they intake microscopic organic matter deposited on the ocean floor floor (Tyler et al., 1992). No evidence of symbiont bacteria was detected in the present specimens (Fujiwara, (Fujiwara, personal observation). Among the four species under study, Katadesmya vincula shows the widest geographical and bathymetrical bathymetrical distributions in the Pacific. This species lives not only on the flat abyssal plain, but also also in hadal habitas, such as in trenches. The re-discovery of Ledellina convexirostris from the Japan Trench is noteworthy since it was collected collected by the R 八r Vityaz in 1966-1969 (Filatova & Schikeyko, 1984). This species lives both the the Japan and Kurile-Kamtchatka trenches. Belyaev (1989) and Vinogradova (1997) concluded that that only 269 もof hadal species are common to two or more of the Aleutian, Kurile- Kamtchatka, Jap 組組d Izu-Bonin trenches. This may be one such example. Another protobranch, Bathypinula vityazi vityazi (Filatova, 1964) [not available in the present material: Coan et al. (2000) consider it a Four Four Protobranch Bivalves in the Japan Trench 93 synonym of Bathyspinula prolata (Smith, 1885) from Challenger St. 256], is found from both the Japan Japan and Izu-Bonin trenches, as well as from the Aleutian and Kurile-Kamchatka trenches, at depths depths between 6450 m and 9335 m (Filatova, 1976). The most abundant species, Yoldiella kaikonis n. sp., is considered to be endemic to the Japan Trench. Trench. No similar-looking species has been described from either of the neighboring trenches. Thus, Thus, it is concluded that the present catch is a mixture of trench-endemic elements and widely widely spread abyssal-hadal species. The fu 旬 re accumulation of specimens and data will draw a clearer picture of the protobranchiate fauna in the Japan Trench and permit discussion of the abundance, abundance, ecology, and zoogeography of the trench bivalves.

Acknowledgements

We owe many thanks to Dr. K. F吋ikura, JAMSTEC, and all other colleague scienti 山 on board the RN Kairei with us. The warmest help of the support t巴am and the efforts of the diving team of ROV Kaiko Kaiko are heartily acknowledged. Dr. T. Sasaki, University Museum, the of University To 匂o, kindly offered offered his skill preparing scanning electron micrographs (Fig. 2B, D, F and H) for publication.

References

Allen, Allen, J. A. & Hannah, F. J. 1986. A reclassification of 白巴 Recent genera of the subclass Protobranchia (: (Mollusca: ). Journal of Conchology 32: 225-249. Allen, Allen, J. A., Sanders, H. L. & Hannah, F. 1995. Studies on the deep-sea Protobranchia (Bivalvia); th 巴 subfamily subfamily Yoldiellinae. Bulletin of the Natural History Museum of London (Zoology) 61: 11-90. Belyaev, Belyaev, G. M. 1989. Deep Sea Trenches and their Fauna. 255 pp. Akademia Nauk, Moscow. (in Russian) Russian) Coan, Coan, E. V., Scott, P. V., & Bernard, F. R. 2000. Bivalve seashells of western North America. Marine bivalve bivalve mollusks from arctic Alaska to B 司 ja California. Santa Barbara Museum of Natural History Monograph 2. Studies in Biodiversi η2: viii + 764 pp. Filatova, Filatova, Z. A. 1976. Structure of the deep-sea genus of bivalve mollusc Spisula (Dall, 1908, Malletiidae) and and their dis 位ibution in 白e ocean. Trudy lnstituta Okeanologii Akademia Nauk SSSR 99: 219-240. (in (in Russian) Filatova, Filatova, Z. A. & Schileyko, A. A. 1984. Size, s佐ucture and distribution of the deep-sea Bivalvia of 仕ie family family Ledellidae (Protobranchia). Trudy Instituta Okeanologii, Akademia Nauk SSSR 119: 106-144. (in (in Russian) Knudsen, Knudsen, J. 1970. The systematics and biology of abyssal and hadal Bivalvia. Galathea Report 11: 1 ”240,

pls. pls. 1』 20. Ockelmann, Ockelmann, K. & Waren, A. 1998. of and biological notes on the bivalve genus Microgloma, with with comments on protobranch nomenclature. Ophelia 48: 1- 24. Okutani, Okutani, T. 1975. Deep-sea bivalves and scaphopods collected from deeper than 2,000 m in th 巴 northwestern northwestern Pacific by the RNs Soyo-Maru and Kaiyo-Maru during the years 1969-1974. Bulletin of of the Tokai Regional Fisheries Research Laboratory (82): 57-87. Okutani, Okutani, T. 1976. Not 巴s and illustrations of four abyssal protobranchiate bivalves collect 巴d from the North North Pacific by the H.M.S. Challenger. Venus (Japanese Journal of Malacology) 35: 24-26. Okutani, Okutani, T. & Kawamura, R. 2002. Abyssal bivalves collected 合om beyond 3,000 m in 仕ie Northwest Pacific Pacific and Shikoku Basins by the RN Soyo-Maru, 1977-1981. Bulletin of the National Science Museum. Series A (Zoology) 28: 1-19. Schileyko, Schileyko, A. A. 1985. Genus Yoldiella auct. as unnatural group (Bivalvia, Protobranchia). Trudy Instituta Okeanologii, Okeanologii, Akadmia Nauk SSSR 120:165-175. (in Russian) Smith, Smith, E. A. 1885. R 巴port on the Lamellibranchiata collected by H.M.S. Challenger during the years

1873-1876. 1873-1876. Report on the Scientific Results of the Iゐ＇ yage of H.M.S. Challenger during the years 1873-1876. 1873-1876. Zoology 13: 1-341, pls. 1-25. 可ler, P. A., Harvey, R., Giles, L. A. & Gage, J. D. 1992. Reproductiv 巴 strategies and diet in deep-sea nuculanid nuculanid protobranchs (Bivalvia: Nuculanoidea) from the Rockall Trough. Marine Biology 114: 571-580. 571-580. Vinogradova, Vinogradova, N. G. 1997. Zoogeography of the abyssal and hadal zones. Advances in Marine Biology 32: 325-387. 325-387. 94 T. Okutani & Y. Fujiwara

Verrill, Verrill, A. E. & Bush, K. J. 1897. Revision of the g巴nera of Ledidae and Nuculidae of the Atlantic coast of of the United States. American Journal of Science, Series 4 3: 51-63. W 紅白， A. 1989. Taxonomic comments on som 巴 protobranch bivalves from the northeastern Atlantic. Sarsia Sarsia 74: 223-259.

(Rec 巴ived March 17, 2003 I Accepted June 5, 2004)

日本海溝から無人潜水調査船「かいこう」によって採集された原鯨類 4 種

奥谷喬司・藤原義弘

要約

2000 年 7 月，海洋研究開発機構（もと海洋科学技術センター）の無人調査船「かいこう」（支援船「か いれい」）によって日本海溝の主に水深 7000 m 台から採集された 4 種の小型の原偲二枚貝類 4 種につい て研究した。

Katadesmia Katadesmia vincula (Dall, 1908) シズクソデガイ 7320 7320 m から 2 個体。これまで，大西洋産の Malletia cuneata (Jeffreys, 1846 ）と同種で汎世界種とされて いたが，太平洋産のものとは別種とされる。既に日本近海の水深 5440-6210 m から報告されているが， 今回の採集は本種の最深記録と思われる。

Neilonella Neilonella profunda n. sp. フカミハトムギソデガイ（新種・新称） 5225 5225 m から 3 個体， 7320 m から l個体。殻は薄質で，殻頂はほぼ中央。後端もあまり尖らない。殻 表に不鮮明な同心円状の輪脈がある。靭帯は双位，前後歯弓の問の無歯域は殆ど認められない。

Ledellina Ledellina convexirostris Filatova & Schileyko, 1984 コトリソデガイ（新称）

5225 5225 m から 1 個体。かつて旧ソ連のヴィチヤズ号が千島・カムチャッカ海溝の水深 5030 ～ 5070 m から採集，記載された種。殻の後端は尖り浅い湾入がある。既に 1969 年ヴイチャズ号によって，日本海 溝の水深 6608 m から採集記録がある。

Yoldiella Yoldiella kaiko 山 n. sp. （新種） カイコウマルソデガイ（新種・新称） 7299 ～ 7333 m の 5 潜航から合計 24 個体。殻長 6.5 mm ，殻高 4.9 mm ，殻幅 3.4 mm （ホロタイプ）。 殻は楕円形を帝ぴ，左右に良く膨れる。後腹隅湾入はない。殻表は微細な成長脈のほかに，顕微鏡的な 断続する放射線条彫刻がある。弾帯受は貧弱で、あるが，内戦帯は大きい。後腹隅は丸く，湾入はない。