Upper Bathyal Gastropods of the Pacific Coast of Northern Honshu
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Deep-sea Fauna and Pollutants off Pacifi c Coast of Northern Japan, edited by T. Fujita, National Museum of Nature and Science Monographs, No. 39, pp. 225-383, 2009 Upper Bathyal Gastropods of the Pacifi c Coast of Northern Honshu, Japan, Chiefl y Collected by R/V Wakataka-maru Kazunori Hasegawa Showa Memorial Institute and Department of Zoology, National Museum of Nature and Science, 4̶1̶1 Amakubo, Tsukuba, Ibaraki, 305̶0005 Japan E-mail: [email protected] Abstract: Gastropods collected chiefl y by the R/V Wakataka-maru of the Fisheries Research Agency with an otter trawl off the Pacifi c coast of northern Honshu, Japan, at depths of 200̶1500 m were examined taxo- nomically based solely on external morphology. About 2740 lots of gastropod specimens from 322 stations were classifi ed into 177 species in 36 families. 103 were identifi ed to species level, whereas 74 could not be identifi ed as any taxa previously known in the northwestern Pacifi c. Eleven nominal taxa are shown here to be synonyms of others. From a biogeographical point of view, the deep-sea gastropod fauna in the survey area is a predominantly boreal fauna, although at least 18 species exhibit wide geographical distribution southwards along the Pacifi c coast of southern Japan. Even disregarding the un-named taxa, 40 species are shown to be endemic to the Pacifi c coast of northern Japan. Key words: Gastropoda, deep-sea, bathyal, northern Honshu, Japan, taxonomy, distribution. Introduction The National Museum of Nature and Science has been carrying out a biological sampling program entitled “Study on Deep-Sea Fauna and Preservation of Deep-Sea Ecosystem” since 1993, to examine and describe the deep-sea fauna of Japan and its adjacent areas. For the fourth term in the program, an area off the Pacifi c coast of northern Honshu, from the Shimokita Penin- sula in Aomori Prefecture to Joban in northern Ibaraki Prefecture, was chosen as the survey area, and intensive samplings were made mainly by the R/V Wakataka-maru of the Fisheries Research Agency (FRA) in cooperation with the Tohoku National Fisheries Research Institute, during the years 2005 to 2008. Considerable numbers of gastropods with detailed position and depth data were obtained at more than 300 stations at depths from 150 to 1500 m, corresponding to the upper bathyal zone. The present paper provides basic and preliminary information on the distribution and variation of all gastropods obtained during the present survey, with illustrations of representative specimens, and forms the basis for a comprehensive study of the gastropod fauna of this region. More detailed work on the taxonomy of problematic species and groups using anatomical charac- ters will be the subject of future studies. Brief review of taxonomical study of gastropods in northeastern Honshu The taxonomical study of the deep-sea molluscan fauna off the Pacifi c coast of northern Hon- shu, including the area known in Japan as “the Sanriku Coast” (from Aomori Prefecture south- wards to Miyagi Prefecture), started in the Meiji era (1868̶1912) based on specimens collected by gill nets set for the Spiny Dogfi sh Squalus acanthias. By the end of the era, more than one thou- sand fi shing boats were engaged in this shark fi shery, and numerous gill nets were set at depths down to 300̶400 fathoms (Toba, 1928 in 1928̶1935). Shell-bearing molluscs, including gastro- pods, captured together with the sharks were gathered by local collectors, and part of this material 226 Kazunori Hasegawa was sent to American malacologists via Yoichiro Hirase in Kyoto for taxonomical studies. This resulted in the description of new species such as Japelion hirasei (Pilsbry, 1901), Neptunea frater (Pilsbry, 1901), Clinopegma magna unicum (Pilsbry, 1905) and Beringius polynematicus Pilsbry, 1907. The deep-sea molluscan fauna of this region was then briefl y summarized by Genzo Toba (Toba, 1928̶1935). Ranji Tiba subsequently continued Toba’s activities in the Sanriku area, while studying northern Pacifi c mollusks more widely, and described many new species himself, includ- ing Volutopsius pallidus Tiba, 1973, Colus kujianus Tiba, 1973, Plicifusus levis Tiba, 1980 and Mohnia iwateana Tiba, 1981 [= Mohnia bella (Ozaki, 1958)]. These were collected from the San- riku region at bathyal depths by commercial trawlers. Besides the activities of these local collec- tors, several scientifi c deep-sea surveys have also been carried out in this area. During the 1906 North Pacifi c Expedition, the Steamer Albatross of the U.S. Commission of Fish and Fisheries visited Japanese waters and trawled at many stations (Dunn, 1996), including two (stations 5050, 5051) off Kinkazan in Miyagi Prefecture, where several new species were discovered, such as Solariella delicata (Dall, 1919), Paraspirotropis simplicissima (Dall, 1907) and Aforia sakhalin- ensis Bartsch, 1945 [= Aforia circinata (Dall, 1873)]. This was followed by Japanese research vessels, such as the R/V Soyo-maru I, with discoveries of Abyssotrophon delicatus (Kuroda, 1953) from off Ishinomaki and Parancistrolepis fujitai (Kuroda, 1931) from off Kinkazan; the R.V. Soyo- maru III, with the discovery of Neptunea nivea Okutani, 1981 from off Kinkazan, and the Russian vessel R/V Vitjaz, with the discoveries of Solariella tuberculata Bagirov, 1995 [= S. delicata (Dall, 1919)], Solariella fera Bagirov, 1995 [= Margarites margaritiferus Okutani, 1964], Abyssotro- phon unicus Egorov, 1993 and A. convexus Egorov, 1994 [both = A. delicatus (Kuroda, 1953)] off Iwate Prefecture. Although modern Japanese research vessels, such as the R/Vs Tansei-maru and Hakuho-maru, have carried out deep-sea research surveys repeatedly in this area in recent years, no signifi cant results have been published yet based on the material they obtained, except for the works by Ishikawa (1970) who reported 13 species of gastropods off the Sanriku Coast at depths of 492̶504 m and 1230̶1250 m obtained by R/V Tansei-maru, and Okutani and Fujikura (2002) who reported molluscs associated with the chemosynthesis-based communities in Japan Trench at abyssal to hadal depths. Additional local faunal studies in this area include those by Ishiyama (1974), who recorded 12 gastropods from off Hachinohe in Aomori Prefecture at depths of 220 m and deeper, and Nemoto and Akimoto (1990), who listed ten gastropods from “bathyal depths” off Joban in Fukushima Prefecture. On the other hand, rather detailed taxonomical studies have been carried out in the sea area Kashima-nada, which abuts the southernmost part of the present survey area, based mainly on specimens gathered by local collectors from commercial bottom trawls. These studies include Shikama (1962), who described 12 new gastropod species and subspecies, and some other occasional papers including Habe and Ito (1965a). Okutani (1964) described six new gastropod species and subspecies from the Kashima-nada, based on material obtained by the R/V Soyo-maru III. Despite all this, however, there has been no comprehensive study to date of the bathyal gastropods of northeastern Japan, and there is thus a considerable degree of confusion in their taxonomy. Materials and Methods Most of the material examined in the present study was obtained during the research cruises of the FRA R/V Wakataka-maru off the Pacifi c coast of northern Honshu, in an area from 36.5˚N to 41˚N at depths of from 150 m to 1500 m by means of otter trawls. Survey stations were basi- cally sited along 12 lines (lines “A” off Hachinohe in Aomori Prefecture though “H” off Hitachi in Ibaraki Prefecture: Fig. 1), at depths of 150, 210, 250, 280, 310, 350, 380, 410, 425, 450, 480, 510, 550, 650, 750 and 900 m, although some stations were omitted from several survey lines (e.g. Bathyal Gastropods of Northern Japan 227 42 Shimokita 41 A Hachinohe B Kuji 40 Miyako C Ofunato 39 D Kesen-numa DE Kinkazan E (Ojika Peninsula) 2000 38 EF 100 200 500 10001500 Soma F FG Onahama 37 G Hitachi GH H 36 Kashima-nada Choshi 35 140 141142 143 144 145 Fig. 1. A map showing the survey area and the sampling lines, with the major place names in northern Honshu that mentioned in the text. 150̶210 m and 550̶900 m from lines “DE”, “EF”, “FG” and “GH”). Deep-sea trawls beyond 900 m (at 1200 and 1500 m) were occasionally added on some lines, and dredge operations were also carried out at some stations (Fig. 2 for the years 2005̶2007). Each station number is thus com- posed of the abbreviated name of vessel (e.g. WA: Wakataka-maru), followed by the year, survey line (A̶H) and the depth. Where “D” is present at the end, this indicates dredge operation. Addi- tional samples collected by earlier surveys of the R/V Wakataka-maru and also by Hyogo Prefec- ture’s T/S Tanshu-maru, which was chartered by the FRA for the same research program 228 Kazunori Hasegawa °N A A A Hachinohe Hachinohe Hachinohe Kuji Kuji B Kuji B B C Miyako C Miyako C Miyako Ofunato Ofunato Ofunato D Kesennuma D Kesennuma D Kesennuma D-E D-E D-E E E E Kinkazan Kinkazan Kinkazan E-F E-F E-F Soma Soma Soma F F F F-G F-G F-G Onahama G Onahama G Onahama G G-H G-H G-H Hitachi Hitachi Hitachi H Otter Trawl H Otter Trawl H Otter Trawl 2005 2006 2007 A1200 A250 A1500 A250 A1500 A A A150 A Hachinohe Hachinohe Hachinohe B750 B410 B1500 Kuji Kuji Kuji B B B310 B C350 C350 C C C Miyako Miyako C900 Miyako C1500 D1500 D1500 D450 Ofunato Ofunato Ofunato D210 D D D Kesennuma Kesennuma D210 Kesennuma DE250 D-E D-E D-E DE380 E1000 DE280 E510 E1200 E E E Kinkazan Kinkazan Kinkazan E-F EF450 E-F E-F EF425 EF250 Soma Soma F650 F1500 Soma F F F FG350 F-G FG510 F-G F-G FG250 Onahama G Onahama G G1200 Onahama G G1500 GH510 GH480 G-H G-H G900 G-H Hitachi Hitachi Hitachi GH380 H1500 H H900 Dredge H H250 Dredge H Dredge 2005 2006 2007 ° E Fig.