Abyssal gastropods in the Sea of Okhotsk (Vetigastropoda and Caenogastropoda)

Author’s Accepted Manuscript Abyssal gastropods in the Sea of Okhotsk (Vetigastropoda and Caenogastropoda) Hiroaki Fukumori, Kazunori Hasegawa, Yasunori Kano www.elsevier.com/locate/dsr2

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S0967-0645(17)30300-4 http://dx.doi.org/10.1016/j.dsr2.2017.09.013 DSRII4315

To appear in: Deep-Sea Research Part II Received date: 10 August 2017 Revised date: 16 September 2017 Accepted date: 17 September 2017 Cite this article as: Hiroaki Fukumori, Kazunori Hasegawa and Yasunori Kano, Abyssal gastropods in the Sea of Okhotsk (Vetigastropoda and C a e n o g a s t r o p o d a ) , Deep-Sea Research Part II, http://dx.doi.org/10.1016/j.dsr2.2017.09.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Abyssal gastropods in the Sea of Okhotsk (Vetigastropoda and Caenogastropoda) Hiroaki Fukumoria,*, Kazunori Hasegawab and Yasunori Kanoa a

Department of Marine Ecosystems Dynamics, Atmosphere and Ocean Research

Institute (AORI), The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan b

Department of Zoology, National Museum of Nature and Science, 4-1-1 Amakubo,

Tsukuba, Ibaraki 305-0005, Japan

Corresponding author* at: Department of Marine Ecosystems Dynamics, Atmosphere and Ocean Research Institute (AORI), The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan. E-mail address: [email protected] (H. Fukumori).

ABSTRACT The joint Russian–German expedition SokhoBio in 2015, on the research vessel Akademik M.A. Lavrentyev, provided the first opportunity to investigate the richness and composition of the abyssal gastropod fauna in the Kuril Basin of the Sea of Okhotsk, from which only a single species has been recorded in the literature. During the expedition, sampling of benthic animals was conducted at eight stations in the Sea of Okhotsk and at three stations in the Pacific (landward slope of the Kuril–Kamchatka Trench) using an Agassiz trawl, an epibentic sledge, and a giant box corer. A total of 417 specimens of ‘prosobranch’ gastropods were taken alive and were classified into 15 families and 70 species of Vetigastropoda and Caenogastropoda. Both abundance and richness were lower than expected in the Kuril Basin compared to the Pacific: 97 specimens belonging to 27 species (11 families) were collected at seven stations in the Kuril Basin, while 286 specimens in 43 species were found from two abyssal stations on the Pacific side of the Kuril Islands. Only six species occurred at abyssal depths on both sides. Familial composition also differed: large-sized buccinids were common only on the Pacific side. The very low levels of dissolved oxygen might explain the low abundance and richness, as well as the scarcity of large species, of Gastropoda in the Kuril Basin. Keywords: Abyssal zone, Benthos, Gastropoda, Kuril Basin, Kuril–Kamchatka Trench, Prosobranchs, SokhoBio, Species composition

1. Introduction The abyssal zone (3,000–6,000 m depth) represents the largest marine habitat and occupies about half of the Earth’s surface (Ramirez-Llodra et al., 2010). Macro- and megabenthos constitute important components of biodiversity on the abyssal sea floor and play significant roles in carbon cycling, phytodetritus consumption and bioturbation (Amon et al., 2016; Beaulieu and Smith, 1998; Rex and Etter, 2010). In general, the number of deep-sea benthic organisms declines exponentially with increasing depth (e.g., Rex et al., 1990), whereas species diversity often peaks at lower bathyal to upper abyssal depths and then decreases towards the hadal zone (Stuart et al., 2003). Many deep-sea taxa have a broad geographic distribution through high dispersal potential as pelagic larvae (Bouchet and Warén, 1994; McClain et al., 2009; Rex and Warén, 1982). Species composition and diversity may yet vary among different parts of the oceans or oceanic basins, partly due to shallower boundaries and different levels of productivity and oxygen concentrations (Jones and Sanders, 1972; Stuart and Rex, 2009). But our understanding of abyssal faunas remains fragmentary due to insufficient sampling (Ebbe et al., 2010). Since the Challenger voyages in the 1870s, numerous deep-sea expeditions have been undertaken in the northwestern Pacific Ocean and its marginal seas (e.g., Belyaev, 1989; Jamieson et al., 2009; Monin, 1983; Ohta and Laubier, 1987; Okutani, 1974). The most intensive sampling of the deep-sea benthos has been conducted in the abyssal plain area south of the Kuril–Kamchatka Trench, where species richness and diversity are considered to be higher than in other areas of the Northwest Pacific (Ebbe et al., 2010). This abyssal fauna has recently been reviewed by the joint German–Russian expedition, KuramBio (Brandt and Malyutina, 2015). Many new and rare species were collected in good condition using various sampling mechanisms during the expedition (Brandt et al., 2015). The same scientific team conducted another expedition, SoJaBio, and reported a number of taxa from the bathyal and abyssal zones of the Sea of Japan (Brandt et al., 2013; Malyutina and Brandt, 2013). These expeditions have made the Sea of Okhotsk as the least explored ocean area in the Northwest Pacific for the abyssal benthos. The Sea of Okhotsk is a semi-closed sea surrounded by the far eastern continental Russia and islands of Sakhalin, Kuril and Hokkaido. It is relatively shallow with an average depth of 821 m (Oguz and Su, 2004), while the Kuril Basin in the south is

mostly below 3,000 m with a maximum depth of 3,374 m (Miyashiro, 1967). The Kuril Basin has two deep-water passages to the Pacific Ocean, namely the Bussol (2,318 m) and Krusenstern (1,920 m) Straits between the Kuril Islands. Water influx through these passages is considered to have a profound influence on the benthic fauna of the basin (Tyler, 2003). Many abyssal species recorded from the basin are deemed to have a wide distribution in the Northwest Pacific (Ushakov, 1950, 1953). This topographic setting provides a clear contrast to the more isolated condition of the Sea of Japan, which is connected with the East China Sea, Sea of Okhotsk and Pacific Ocean through much shallower straits (< 130 m; Nishimura, 1969). Gastropod molluscs are one of the main components of the macrobenthic fauna in the deep sea (e.g., Brandt et al., 2013, 2015; Gage and Tyler, 1991). Yet species composition of gastropods has been virtually unknown for the Kuril Basin. Four historical deep-sea expeditions were conducted in the Sea of Okhotsk by the American research vessel (R/V) Albatross in 1906 and Russian R/Vs Gagara (1932) and Vityaz (1949 and 1952) (Anonymous, 1907; Dall, 1907; Monin, 1983; Ushakov, 1953). Those expeditions provided rare opportunities to obtain abyssal species by trawling, dredging and grabbing in the Kuril Basin. However, only one gastropod, Paraspirotropis simplicissima (Dall, 1907), was included in the list of about 50 such animals species from the basin (Ushakov, 1950, 1953). The Russian–German deep-sea expedition SokhoBio 2015 (Sea of Okhotsk Biodiversity Studies 2015) on board the R/V Akademik M.A. Lavrentyev was then carried out to survey bathyal and abyssal faunas in the Sea of Okhotsk and Kuril–Kamchatka Trench area. The principal aim of the expedition was to investigate the composition, biodiversity and biogeography of benthic organisms in the Kuril Basin (Malyutina et al., 2015). By employing such sampling gear as a giant box corer, an epibenthic sledge, and an Agassiz trawl (see Brandt et al., 2013, 2015), numerous invertebrates including many gastropod species of various sizes, were successfully collected. The present paper first describes the species composition of ‘prosobranch’ gastropods (or the Gastropoda excluding the clade Heterobranchia) in the Kuril Basin. Also documented are lower bathyal and abyssal prosobranchs on the landward slope of the Kuril–Kamchatka Trench near the Bussol Strait. This enables us to compare species composition between the abyssal benthic faunas of the Sea of Okhotsk and Pacific Ocean for evaluating the degree of connectivity (Tyler, 2003).

2. Material and methods The Kuril Basin is a typical back-arc basin behind the Kuril Islands (Gnibidenko, 1985). Its seafloor is flat at depths of about 3,200 to 3,300 m (Tyler, 2002) with sediments consisting mainly of clays and diatomaceous oozes (Zenkevich, 1963). During the SokhoBio expedition on the R/V Akademik M.A. Lavrentyev (71st cruise, 6th July to 6th August 2015), sampling of benthic animals was made at a total of 11 stations: eight in the Sea of Okhotsk, one near the deepest part of the Bussol Strait (on the Pacific side) and two on the landward slope of the Kuril–Kamchatka Trench (Fig. 1). These comprised nine stations at abyssal depths below 3,000 m and one each in the Sea of Okhotsk and Bussol Strait at bathyal depths (1,694–1,700 m and 2,266–2,348 m, respectively). The following sampling gear were deployed at every station: a giant box corer (BC; 0.25 m2), an epibenthic sledge (EBS; see Brandt et al., 2013), and an Agassiz trawl (AGT; 3.5 m wide, 0.7 m high, 10 mm mesh). Four BC, two EBS and two AGT samplings were typically conducted for each station, resulting in the acquisition of 44 BC, 21 EBS and 19 AGT sediment samples (Malyutina et al., 2015). Of these, 37 BC, 15 EBS and 14 AGT were from the Sea of Okhotsk, including 33 BC, 13 EBS and 12 AGT at seven abyssal stations in the Kuril Basin. Macroscopic specimens of the Gastropoda were picked out of the collected sediment on the deck of the vessel. The sediment was then carefully sieved through meshes of various pore sizes (300–1,000 µm) to obtain different size fractions. Sieved fractions from BC and AGT were kept ice-cold and examined for gastropods under a dissecting microscope in the on-board laboratory, while EBS samples were sorted after fixation in 96% ethanol. Sorted snails were boiled in 70–90°C water for 0.1–0.5 min before ethanol (96–99%) preservation or directly fixed in 4% seawater formalin. Gastropod material examined in this study is currently stored at Atmosphere and Ocean Research Institute, The University of Tokyo, Japan (AORI), except a single specimen of Adeuomphalus sp., which was identified through photographs from Dr. Alexei V. Chernyshev at A.V. Zhirmunsky Institute of Marine Biology, Far East Division, Russian Academy of Sciences. Live-taken gastropods were identified at species or generic level based on the shell, operculum and soft parts by referring to previous taxonomic and faunal studies

(e.g., Bartsch, 1941; Bouchet and Warén, 1986; Dall, 1907, 1925; Egorov, 1993, 1994; Golikov and Sirenko, 1998; Hasegawa, 2001, 2005, 2009; Hasegawa and Okutani, 2011; Hasegawa et al., 2017; Kantor and Sysoev, 1991, 2006; Kosyan and Kantor, 2012, 2015; Lus, 1976; Okutani, 1966; Sysoev and Kantor, 1987; Warén, 1989, 1991, 1996). Familial classification follows Bouchet and Rocroi (2005), Bouchet et al. (2011), Kano (2008), Kano et al. (2009), and Kantor et al. (2012). The numbers of specimens and species were counted for each station. Two naticid and eight mangeliid specimens were too young to be identified to a genus (with less than one teleoconch whorl) and were excluded from the counts. Heterobranch gastropods from the expedition, approximately ten species in total, will be treated elsewhere (Chaban et al., #####). 3. Results A total of 417 specimens of prosobranch gastropods were taken alive from five giant box corer (BC), sixteen epibenthic sledge (EBS) and fifteen Agassiz trawl (AGT) samples at eleven stations (Tables 1, 2). Thirty-nine BC, five EBS and four AGT samples did not contain live prosobranch material. Ninety-nine specimens out of 417 (23.7%) were collected at eight stations in the Sea of Okhotsk (St. 1–7 and 11) and remaining 318 (76.4%) from three stations in the Pacific Ocean (St. 8–10). The number of specimens at each station ranged from one (St. 3) to 46 (St. 1) in the former area (average and SD: 12.4 ± 13.7). The stations on the Pacific side yielded generally more numerous individuals: 32 (St. 8) to 210 (St. 9) with an average of 106.0 (SD: 72.8). Prosobranchs were less abundant at the bathyal sites (St. 5 and 8) than at the abyssal ones in both the Sea of Okhotsk and the Pacific Ocean; two bathyal and 97 abyssal specimens were collected from the Sea of Okhotsk and 32 bathyal and 286 abyssal from the Pacific (Table 2). These specimens were classified into 70 species in 15 families (Table 2; Figs. 2–5). Each species was represented by one to 35 specimens. Forty-four species (62.9%) were represented by five or fewer specimens; 28 of these were singletons (40.0%). Species composition differed greatly from site to site and 52 species (74.3%) were collected from a single station. The highest species richness was recorded at St. 1 (14 species) in the Sea of Okhotsk and St. 9 (32) in the Pacific Ocean. The total number of species from the former sea (29) was smaller than that of the latter (47); 27 and 43 of

these were collected at abyssal depths in the respective areas. Only six species, all exclusively from the abyssal zone, occurred in both the Sea of Okhotsk and Pacific Ocean: Seguenzia sp., Euspira sp. 5, Pararetifusus sp. 2, Granotoma sp. 1, Paraspirotropis simplicissima and Mangeliidae sp. (Table 2). Only two out of 27 species from the Kuril Basin have been recorded in previous faunal studies for other areas: Pseudopolinices sp. and Paraspirotropis simplicissima from the bathyal slopes of the Kuril–Kamchatka and Japan Trenches (Hasegawa, 2009: figs. 114–117; Kantor and Sysoev, 2006: pl. 112, fig. J). Table 3 summarizes the familial composition of prosobranchs collected during the SokhoBio expedition. Mangeliidae was the most abundant and species-rich among 11 families recorded from the Kuril Basin; 36 out of 97 prosobranch specimens from the basin (37.1%) belonged to eight species in seven mangeliid genera (see also Table 2). This family was the most abundant also on the Pacific side (107 out of 318 specimens; 33.6%), whereas Buccinidae comprised the highest number of species there (15 in ten genera). The families Seguenziidae, Naticidae, Buccinidae, and Mangeliidae contained species with distributions on both sides of the Kuril Islands. Pseudococculinidae, Newtoniellidae and Turridae were each represented by a single species that occurred only in the Kuril Basin; on the other hand, Belomitridae, Volutomitridae and Pseudomelatomidae were restricted to the Pacific stations. 4. Discussion The present study provides the first insight into the species richness and composition of the abyssal gastropod fauna in the Kuril Basin of the Sea of Okhotsk, from which only a single lot of Paraspirotropis simplicissima had previously been reported (Dall, 1907; Ushakov, 1950, 1953). A total of 97 specimens belonging to 27 prosobranch species were newly collected from the basin during the SokhoBio expedition. Both numbers of individuals and species collected were, however, surprisingly few given the sampling effort invested. Although nearly four times more numerous hauls by trawl, epibenthic sledge and box corer were obtained in the Sea of Okhotsk than in the Kuril–Kamchatka Trench area (Malyutina et al., 2015), the numbers of specimens and species collected were only one-third and a little more than a half, respectively (Table 2).

As a general rule, the oxygen concentration of bottom water strongly influences both abundance and species diversity of deep-sea macrobenthos including the Gastropoda (e.g., Levin and Gage, 1998; Thistle, 2003). This seems to explain the meagre prosobranch fauna in the Kuril Basin where the seafloor is characterized by very low levels of dissolved oxygen (Freeland et al., 1998; Kamenev ####; Zhang et al., 2001). The tendency of decreasing density, biomass and species richness of benthos with increasing depth has actually been connected to the decrease of oxygen concentration in the Sea of Okhotsk (Zenkevitch, 1963). Another possible explanation for the low benthic biomass is the particularly low level of surface primary production in the central part of the sea (Tyler, 2002). The species composition of abyssal gastropods in the Sea of Okhotsk seems to greatly differ from that of the Kuril–Kamchatka Trench area. Only six out of 27 prosobranch species from the Kuril Basin were also recognized from the SokhoBio stations on the Pacific side (Table 2). The Sea of Okhotsk is connected to the Pacific Ocean by two deep straits at about 2,000 m depth (Nishimura, 1969) and water influx through these passages has been suggested to influence the benthic fauna of the basin (Tyler, 2003). However, the water mass of the basin may well be isolated (Zenkevitch, 1963) as shown by different vertical profiles of dissolved oxygen from lower bathyal to abyssal depths in the Sea of Okhotsk and Kuril–Kamchatka Trench area (Zhang et al., 2001). Inappropriate taxonomic assignments or lumping might have led to the previous understanding that many of the animal species in the Kuril Basin have a wide distribution in the Northwest Pacific (Ushakov, 1950, 1953). Regardless, too few gastropod specimens were available to determine the exact number or proportion of species endemic to the Kuril Basin. Familial composition also differed between the abyssal gastropod samples from the two regions, potentially reflecting differences in the body size, feeding ecology and/or tolerance to environmental stresses among families. The Mangeliidae were most abundant in both regions, while the Buccinidae were numerous and speciose only in the Pacific (Table 3). Buccinids are scavengers of particularly large sizes among bathyal and abyssal gastropods (one to over ten centimetres; e.g., Aguzzi et al., 2012; Haseagawa, 2009; Kantor and Sysoev, 2006). The maximum size of deep-sea snails is known to decrease with decreasing concentration of dissolved oxygen (e.g., McClain and Rex, 2001).

Dall (1907) described Paraspirotropis simplicissima (as Pleurotomella simplicissima), which represents the only gastropod taxon described from the Kuril Basin. The original description of the species referred to the Albatross station ‘5050’ on 29th September 1906 at the depth of 3,292 m in the Sea of Okhotsk as the type locality (Dall, 1907). That station number seems to be erroneously written instead of the actual 5030 (see Anonymous, 1907); the number 5050 was assigned to a station on 10th October 1906 at a much shallower (486 m) site off Kinkazan, Honshu Island, Japan, in an area where P. simplicissima has never been collected (e.g., Hasegawa, 2009). The syntypes deposited in the Smithsonian National Museum of Natural History (Fig. 5A, B) are similar to the new material from the Kuril Basin (Fig. 5E,F). Other species recovered in this study appear to be new to science (Table 2). However, deep-sea gastropods often show considerable morphological variation within species (e.g., Bouchet and Warén, 1986; Hasegawa, 2009; Hasegawa and Okutani, 2011) and the presence of cryptic species has also been documented (e.g., Castelin et al., 2010; Quattro et al., 2001). More detailed taxonomic and population studies, based on molecular and anatomical data from the present material as well as from specimens from the Northwest Pacific and its other marginal seas, are essential to further understand the biogeographic characteristics of the abyssal gastropod community in the Sea of Okhotsk. Acknowledgements We would like to thank Marina V. Malyutina, Angelika Brandt and Victor V. Ivin for organizing the SokhoBio expedition. Our special thanks also go to the captain and crew of the R/V Akademik M.A. Lavrentyev for their professional work and to all participants of the cruise for collecting, sorting and processing the samples. Tsuyoshi Takano and Anders Warén assisted with the identification of some gastropod specimens, and Alexei V. Chernyshev provided the photographs of Adeuomphalus sp. for our examination and inclusion in this paper. Invaluable comments on the manuscript were made by Yuri I. Kantor, Niall Mateer and Anders Warén. Financial support was provided by the Japan Society for the Promotion of Science (JSPS KAKENHI grants nos. 23570126, 26291077 and 15H04412). This is the SokhoBio publication ###.

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characterization of the enigmatic planispiral snail genus Adeuomphalus (Vetigastropoda: Seguenzioidea). J. Moll. Stud. 75, 397–418. Kantor, Yu.I., Sysoev, A.V., 1991. Mollusks of the genus Antiplanes (Gastropoda: Turridae) of the northwestern Pacific Ocean. Nautilus 105, 119–146. Kantor, Yu.I., Sysoev, A.V., 2006. Marine and brackish water Gastropoda of Russia and adjacent countries: an illustrated catalogue. KMK Scientific Press, Moscow. Kantor, Yu.I., Puillandre, N., Rivasseau, A., Bouchet, P., 2012. Neither a buccinid nor a turrid: A new family of deep-sea snails for Belomitra P. Fischer, 1883 (Mollusca, Neogastropoda), with a review of Recent Indo-Pacific species. Zootaxa 3496, 1–64. Kosyan, A.R., Kantor, Yu.I., 2012. Revision of the genus Plicifusus Dall, 1902 (Gastropoda: Buccinidae). Ruthenica 22, 55–92. Kosyan, A.R., Kantor, Yu.I., 2015. Notes on the abyssal genus Fusipagoda Habe et Ito, 1965 (Neogastropoda: Buccinidae) from the North Pacific. Ruthenica 25, 77–87. Levin, L.A., Gage, J.D., 1998. Relationships between oxygen, organic matter and the diversity of bathyal macrofauna. Deep-Sea Res. II 45, 129–163. Lus, V.J., 1976. New and rare deepsea species Buccinum (fam. Buccinidae) from the regions of the Kurilo–Kamchatka and Japan Trenches. Tr. Inst. Okeanol. Akad. Nauk SSSR. 99, 71–84. Malyutina, M.V., Brandt, A., 2013. Introduction to SoJaBio (Sea of Japan Biodiversity Studies). Deep-Sea Res. II 86-87, 1–9. Malyutina, M.V., Brandt, A., Ivin, V.V., 2015. The Russian–German deep-sea expedition SokhoBio (Sea of Okhotsk Biodiversity Studies) to the Kurile Basin of the Sea of Okhotsk on board of the R/V Akademik M.A. Lavrentyev 71st Cruise, July 6th–August 6th, 2015 (Cruise Report). McClain, C.R., Rex, M.A., 2001. The relationship between dissolved oxygen concentration and maximum size in deep-sea turrid gastropods: an application of quantile regression. Mar. Biol. 139, 681–685. McClain, C.R., Lundsten, L., Ream, M., Barry, J., DeVogelaere, A., 2009. Endemicity, biogeography, composition, and community structure on a Northeast Pacific seamount. PLoS ONE 4, e4141. Monin, A.S. (Ed.), 1983. Research vessel “Vityaz” and her expeditions, 1949–1979. Nauka Publishing House, Moscow (In Russian).

Miyashiro, A., 1967. Orogeny, regional metamorphism, and magmatism in the Japanese islands. Medd. Dan. Geol. Foren. 17, 390–446. Nishimura, S., 1969. The zoogeographical aspects of the Japan Sea, Part V. Publ. Seto Mar. Biol. Lab. 17, 67–142. Oguz, T., Su, J., 2004. Semi-enclosed seas, islands and Australia panregional overview (S). In: Robinson, A.R., Brink, K.H. (Eds.), The sea, vol. 14A: The global coastal ocean: Interdisciplinary regional studies and syntheses. Harvard University Press, Cambridge, Massachusetts, pp. 83–116. Ohta, S., Laubier, L., 1987. Deep biological communities in the subduction zone of Japan from bottom photographs taken during “nautili” dives in the Kaiko project. Earth Planet. Sci. Lett. 83, 329–342. Okutani, T., 1966. Archibenthal and abyssal Mollusca collected by the RV Soyo-Maru from Japanese waters during 1964. Bull. Tokai Reg. Fish. Res. Lab. 46, 1–32. Okutani, T., 1974. Review and new records of abyssal and hadal molluscan fauna in Japanese and adjacent waters. Venus 33, 23–39. Quattro, J.M., Chase, M.R., Rex, M.A., Greig, T.W., Etter, R.J., 2001. Extreme mitochondrial DNA divergence within populations of the deep-sea gastropod Frigidoalvania brychia. Mar. Biol. 139, 1107–1113. Ramírez-Llodra, E., Brandt, A., Danovaro, R., Escobar, E., German, C.R., Levin, L.A., Martinez Arbizu, P., Menot, L., Buhl-Mortensen, P., Narayanaswamy, B.E., Smith, C.R., Tittensor, D.P., Tyler, P.A., Vanreusel, A., Vecchione, M., 2010. Deep, diverse and definitely different: unique attributes of the world's largest ecosystem. Biogeoscience 7, 2851–2899. Rex, M.A., Etter, R.J., 2010. Deep-sea biodiversity: pattern and scale. Harvard University Press, Cambridge, Massachusetts. Rex, M.A., Warén, A., 1982. Planktotrophic development in deep-sea prosobranch snails from the western North Atlantic. Deep-Sea Res. 29, 171–184. Rex, M.A., Etter, R.J., Nimeskern, Jr., P.W., 1990. Density estimates for deep-sea gastropod assemblages. Deep-Sea Res. 37, 555–569. Stuart, C.T., Rex, M.A., 2009. Bathymetric patterns of deep-sea gastropod species diversity in 10 basins of the Atlantic Ocean and Norwegian Sea. Mar. Ecol. 30, 164–180. Stuart, C.T., Rex, M.A., Etter, R.J., 2003. Large-scale spatial and temporal patterns of

deep-sea benthic species diversity. In: Tyler, P.A. (Ed.), Ecosystems of the world, vol. 28: Ecosystems of the deep oceans. Elsevier Science, Amsterdam, The Netherlands, pp. 295–312. Sysoev, A.V., Kantor, Yu.I., 1987. Deep-sea gastropods of the genus Aforia (Turridae) of the Pacific: species composition, systematics, and functional morphology of the digestive system. Veliger 30, 105–126. Thistle, D., 2003. The deep-sea floor: an overview. In: Tyler, P.A. (Ed.), Ecosystems of the world, vol. 28: Ecosystems of the deep oceans. Elsevier Science, Amsterdam, The Netherlands, pp. 5–38. Tyler, P.A., 2002. Deep-sea Eukaryote ecology of the semi-isolated basins off Japan. J. Oceanogr. 58, 333–341. Tyler, P.A., 2003. The peripheral deep seas. In: Tyler, P.A. (Ed.), Ecosystems of the world, vol. 28: Ecosystems of the deep oceans. Elsevier Science, Amsterdam, The Netherlands, pp. 261–293. Ushakov, P.V., 1950. Abyssal fauna of the Sea of Okhotsk. Doklady Akad. Nauk, SSSR. 71, 971–974 (In Russian). Ushakov, P.V., 1953. Fauna of the sea of Okhotsk and conditions of its existence. AN SSSR Nauka, Moscow (In Russian). Warén, A., 1989. New and little known Mollusca from Iceland. Sarsia 74, 1–28. Warén, A., 1991. New and little known <> gastropods from the Mediterranean Sea and the adjacent Atlantic Ocean. Boll. Malacologico 27, 149–248. Warén, A., 1996. New and little known Mollusca from Iceland and Scandinavia. Part 3. Sarsia 81, 197–245. Zenkevitch, L., 1963. Biology of the Seas of the USSR. InterScience, New York. Zhang, Y., Amakawa, H., Nozaki, Y., 2001. Oceanic profiles of dissolved silver: precise measurements in the basins of western North Pacific, Sea of Okhotsk, and the Japan Sea. Mar. Chem. 75, 151–163.

Figure captions Fig. 1. Map of sampling sites (Stations 1–11) during SokhoBio expedition on R/V Akademik M.A. Lavrentyev. Fig. 2. Vetigastropods and caenogastropods collected during SokhoBio expedition: Seguenziidae, ‘skeneimorph seguenzioids’, Pseudococculinidae, Eulimidae, Naticidae, Newtoniellidae and Muricidae. (A) Seguenzia sp., St. 1-8, 6.7 mm; (B) Carenzia sp., St. 10-8, 4.8 mm; (C) Anekes sp., St. 7-3, 0.8 mm; (D) Granigyra sp. 1, St. 11-6, 3.0 mm; (E) Granigyra sp. 2, St. 10-8, 6.6 mm; (F) Lissotesta sp., St. 9-7, 1.3 mm; (G) Adeuomphalus sp., St. 7-4, 1.5 mm; (H) Seguenzioidea sp., St. 10-6, 8.5 mm; (I) Pseudococculinidae sp., St. 4-10, 1.2 mm; (J) Eulima sp. 1, St. 2-8, 6.4 mm; (K) Eulima sp. 2, St. 9-7, 2.6 mm; (L) Eulimidae sp., St. 10-6, 2.2 mm; (M) Euspira nux, St. 9-10, 16.1 mm; (N) Euspira sp. 1, St. 8-6, 13.6 mm; (O) Euspira sp. 2, St. 10-6, 13.1 mm; (P) Euspira sp. 2 (empty shell), St. 10-8, 28.5 mm; (Q) Euspira sp. 3, St. 1-8, 12.6 mm; (R) Euspira sp. 4, St. 1-8, 5.3 mm; (S) Euspira sp. 5, St. 2-7, 6.3 mm; (T) Pseudopolinices sp., St. 1-8, 8.6 mm; (U) Cryptonatica sp., St. 9-10, 15.6 mm; (V) Cerithiella sp., St. 2-9, 2.3 mm; (W) Cerithiella sp. (empty shell), St. 2-9, 31.9 mm; (X) Abyssotrophon longisiphon, St. 9-10, 16.7 mm; (Y) Abyssotrophon cf. edzoevi, St. 9-10, 30.9 mm; (Z) Abyssotrophon sp., St. 1-9, 3.4 mm. Sizes represent shell height except in H (shell diameter) and I (shell length). Fig. 3. Caenogastropods collected during SokhoBio expedition: Buccinidae and Belomitridae. (A) Bathyancistrolepis trochoideus, St. 9-10, 23.0 mm; (B) Bathyancistrolepis sp., St. 2-9, 24.2 mm; (C) Parancistrolepis sp., St. 9-10, 19.5 mm; (D) Ovulatibuccinum sp. 1, St. 9-7, 29.3 mm; (E) Ovulatibuccinum sp. 2, St. 1-10, 12.5 mm; (F) Buccinum rausanum, St. 8-6, 51.6 mm; (G) Buccinum lamelliferum, St. 9-10, 65.0 mm; (H) Buccinum sp., St. 9-10, 25.2 mm; (I) Fusipagoda sp., St. 9-9, 32.9 mm; (J) Fusipagoda sp., St. 9-10, 34.7 mm; (K) Fusipagoda sp., St. 9-10, 36.3 mm; (L) Pararetifusus sp. 1, St. 3-8, 17.1 mm; (M) Pararetifusus sp. 2, St. 9-10, 17.8 mm; (N) Pararetifusus sp. 2, St. 11-7, 7.6 mm; (O) Plicifusus sp. 1, St. 8-6, 17.7 mm; (P) Plicifusus sp. 2, St. 8-6, 21.6 mm; (Q)

Neptunea sp., St. 9-10, 100.1 mm; (R) Calliloncha sp. 1, St. 10-8, 34.6 mm; (S) Calliloncha sp. 2, St. 9-9, 12.5 mm; (T) Bayerius sp. 1, St. 10-8, 27.2 mm; (U) Bayerius sp. 2, St. 10-8, 18.1 mm; (V) Belomitra cf. viridis, St. 9-9, 41.4 mm. Sizes represent shell height. Fig. 4. Caenogastropods collected during SokhoBio expedition: Volutomitridae, Cancellariidae and Mangeliidae. (A) Volutomitra groenlandica alaskana, St. 9-10, 18.9 mm; (B) Admete sp. 1, St. 9-9, 6.2 mm; (C) Admete sp. 2, St. 1-9, 4.5 mm; (D) Admete sp. 3, St. 1-9, 4.3 mm; (E) Admete sp. 4, St. 9-9, 4.8 mm; (F) Iphinopsis choshiensis, St. 9-9, 4.2 mm; (G) Curtitoma cf. bartschi, St. 9-10, 11.8 mm; (H) Curtitoma sp. 1, St. 10-8, 6.7 mm; (I) Curtitoma sp. 2, St. 4-2, 8.6 mm; (J) Obesotoma sp. 1, St. 1-9, 9.0 mm; (K) Obesotoma sp. 1, St. 1-9, 5.4 mm; (L) Obesotoma sp. 2, St. 11-7, 9.7 mm; (M) Granotoma sp. 1, St. 10-6, 8.6 mm; (N) Granotoma sp. 1, St. 1-8, 3.9 mm; (O) Granotoma sp. 2, St. 10-6, 8.3 mm; (P) Granotoma sp. 3, St. 5-3, 5.6 mm; (Q) Granotoma sp. 4, St. 9-10, 10.5 mm; (R) Oenopota sp., St. 1-11, 22.6 mm; (S) Vitjazinella sp. 1, St. 4-3, 7.3 mm; (T) Vitjazinella sp. 1, St. 7-11, 8.6 mm; (U) Vitjazinella sp. 2, St. 9-9, 8.0 mm; (V) Vitjazinella sp. 2, St. 9-9, 6.7 mm; (W) Vitjazinella sp. 3, St. 10-6, 8.9 mm. Sizes represent shell height. Fig. 5. (A, B) Syntypes of Pleurotomella simplicissima Dall, 1907, R/V Albatross, St. 5030 (not ‘5050’; see Discussion), 3,292 m, 46°29.5´N, 145°46.0´E, the Sea of Okhotsk, USNM-110442 (A: 25.4 mm, B: 24.4 mm). (C–P) Caenogastropods collected during SokhoBio expedition: Mangeliidae, Turridae, Cochlespiridae and Pseudomelatomidae. (C) Paraspirotropis simplicissima, St. 9-9, 32.1 mm; (D) P. simplicissima, St. 9-9, 26.4 mm; (E) P. simplicissima (empty shell), St. 1-10, 20.7 mm; (F) P. simplicissima, St. 1-11, 11.9 mm; (G) Mangeliidae sp. (empty shell), St. 9-9, 15.0 mm; (H) Mangeliidae sp., St. 9-7, 7.3 mm; (I) Mangeliidae sp., St. 7-4, 4.1 mm; (J) Cryptogemma sp., St. 5-6, 7.4 mm; (K) Aforia cf. abyssalis, St. 9-9, 38.1 mm; (L) Aforia sp. 1, St. 9-10, 12.7 mm; (M) Aforia? sp. 2, St. 1-8, 8.2 mm; (N) Antiplanes obliquiplicata, St. 9-9, 38.1 mm; (O) Antiplanes obliquiplicata, St. 9-10, 40.2 mm; (P) Plicisyrinx sp., St. 9-9, 8.2 mm. Sizes represent shell height.

Table 1 ‘Gear stations’ of SokhoBio expedition with prosobranch gastropods; BC – giant box corer, EBS – epibenthic sledge, AGT – Agassiz trawl.

Station

Gear station

Gear

Latitude (°N)

Longitude (°E)

Depth (m)

Date

1

1-8 1-9 1-10 1-11 2-7 2-8 2-9 3-8 3-9 4-2 4-3 4-9 4-10 5-3 5-6 6-6 6-8 6-9 7-3 7-4 7-11 8-7 9-1 9-5 9-6 9-7 9-9 9-10 10-1 10-5 10-7 10-8 10-9 11-6 11-7 11-10

EBS EBS AGT AGT EBS EBS AGT AGT EBS AGT AGT EBS EBS BC EBS EBS AGT AGT EBS EBS AGT AGT BC BC EBS EBS AGT AGT BC EBS EBS AGT AGT EBS AGT BC

46°08.44´–46°08.88´ 46°05.04´–46°08.73´ 46°09.00´–46°09.04´ 46°08.74´–46°09.05´ 46°40.76´–46°40.96´ 46°41.09´–46°41.16´ 46°40.64´–46°41.18´ 46°37.83´–46°38.09´ 46°37.82´–46°38.00´ 47°11.80´–47°12.14´ 47°11.22´–47°12.04´ 47°11.95´–47°12.13´ 47°12.04´–47°12.21´ 48°37.20´ 48°37.39´–48°37.47´ 48°03.20´–48°03.26´ 48°00.16´–48°02.53´ 48°02.34´–48°03.01´ 46°56.56´–46°56.79´ 46°57.47´–46°57.49´ 46°57.01´–46°57.03´ 46°36.38´–46°36.47´ 46°16.08´ 46°16.10΄ 46°16.10´–46°16.12´ 46°16.07´–46°16.16´ 46°16.28´–46°16.51´ 46°16.42´–46°16.72´ 46°06.90´ 46°07.31´–46°07.41´ 46°05.83´–46°06.03´ 46°05.78´–46°06.50´ 46°05.46´–46°06.24´ 45°36.79´–45°36.88´ 45°36.93´–45°37.86´ 45°36.30΄

145°59.26´–146°00.26´ 146°00.23´–146°00.47´ 145°59.63´–146°00.46´ 145°59.51´–146°00.79´ 147°28.28´–147°28.47´ 147°27.39´–147°27.71´ 147°27.87´–147°28.76´ 148°39.73´–149°00.67´ 148°59.36´–148°59.82´ 149°36.75´–149°37.52´ 149°37.01´–149°38.06´ 149°36.99´–149°37.14´ 149°36.75´–149°36.95´ 150°00.30´ 150°00.39´–150°00.65´ 150°00.52´–150°00.58´ 150°00.10´–150°00.46´ 149°59.79´–150°00.31´ 151°04.86´–151°05.01´ 151°04.92´–151°05.07´ 151°04.30´–151°05.25´ 151°33.75´–151°34.62´ 152°02.06´ 152°02.10´ 152°02.71´–152°03.04´ 152°03.10´–152°03.32´ 152°03.33´–152°04.26´ 152°03.04´–152°03.88´ 152°03.50´ 152°11.29´–152°11.54´ 152°14.44´–152°14.58´ 152°14.14´–152°15.22´ 152°13.54´–152°13.60´ 146°22.50´–146°22.59´ 146°21.90´–146°22.88´ 146°23.10΄

3,307 3,307 3,305 3,304–3,305 3,351–3,353 3,351–3,352 3,351–3,352 3,362–3,363 3,363 3,366 3,366 3,366 3,366 1,700 1,694–1,695 3,347 3,347–3,351 3,350 3,299 3,300 3,300–3,303 2,350–2,358 3,432 3,428 3,386–3,377 3,371–3,377 3,347–3,356 3,360–3,361 4,741 4,681–4,702 4,769–4,798 4,796–4,803 5,006–5,009 3,210 3,211–3,217 3,206

10 July 2015 10 July 2015 10 July 2015 11 July 2015 13 July 2015 13 July 2015 13 July 2015 15 July 2015 15 July 2015 16 July 2015 16 July 2015 17 July 2015 17 July 2015 18 July 2015 18 July 2015 20 July 2015 21 July 2015 21 July 2015 22 July 2015 22 July 2015 23 July 2015 24 July 2015 25 July 2015 26 July 2015 26 July 2015 26 July 2015 27 July 2015 27 July 2015 27 July 2015 28 July 2015 29 July 2015 29 July 2015 29 July 2015 1 August 2015 1 August 2015 2 August 2015

2

3 4

5 6

7

8 9

10

11

Table 2 Number of specimens collected for each species at SokhoBio stations.

Family

Species

Vetigastropoda Seguenziidae ‘Skeneimorph seguenzioids’

Pseudococculinidae Caenogastropoda Eulimidae

Naticidae

Newtoniellidae Buccinidae

Belomitridae Muricidae

Cancellariidae

Volutomitridae Mangeliidae

Cochlespiridae

Pseudomelatomidae Turridae Total number of specimens Total number of species *

*

Seguenzia sp. Carenzia sp. Adeuomphalus sp. Anekes sp. Granigyra sp. 1 Granigyra sp. 2 Lissotesta sp. Seguenzioidea sp. Pseudococculinidae sp. Eulima sp. 1 Eulima sp. 2 Eulimidae sp. Euspira nux (Okutani, 1964) Euspira sp. 1 Euspira sp. 2 Euspira sp. 3 Euspira sp. 4 Euspira sp. 5 Pseudopolinices sp. Cryptonatica sp. Cerithiella sp. Bathyancistrolepis trochoideus (Dall, 1907) Bathyancistrolepis sp. Parancistrolepis sp. Ovulatibuccinum sp. 1 Ovulatibuccinum sp. 2 Buccinum lamelliferum Lus, 1976 Buccinum rausanum Shikama, 1957 Buccinum sp. Fusipagoda sp. Pararetifusus sp. 1 Pararetifusus sp. 2 Plicifusus sp. 1 Plicifusus sp. 2 Neptunea sp. Calliloncha sp. 1 Calliloncha sp. 2 Bayerius sp. 1 Bayerius sp. 2 Belomitra cf. viridis (Okutani, 1966) Abyssotrophon cf. edzoevi Egorov, 1994 Abyssotrophon longisiphon Egorov, 1993 Abyssotrophon sp. Iphinopsis choshiensis (Habe, 1958) Admete sp. 1 Admete sp. 2 Admete sp. 3 Admete sp. 4 Volutomitra groenlandica alaskana Dall, 1902 Curtitoma cf. bartschi (Bogdanov, 1985) Curtitoma sp. 1 Curtitoma sp. 2 Granotoma sp. 1 Granotoma sp. 2 Granotoma sp. 3 Granotoma sp. 4 Obesotoma sp. 1 Obesotoma sp. 2 Oenopota sp. Vitjazinella sp. 1 Vitjazinella sp. 2 Vitjazinella sp. 3 Paraspirotropis simplicissima (Dall, 1907) Mangeliidae sp. Aforia cf. abyssalis Sysoev & Kantor, 1987 Aforia sp. 1 Aforia? sp. 2 Antiplanes obliquiplicata Kantor & Sysoev, 1991 Plicisyrinx sp. Cryptogemma sp.

Unassigned to families (see Kano et al., 2009).

St. 1

St. 2

St. 3

Sea of Okhotsk St. 4 St. 5 St. 6 St. 7 St. 11

6

1

1

Total

St. 8

8

Pacific Ocean St. 9 St. 10 Total 5 3

1 5

1 1

1

6 2 1 1 1

1

1 1 1

1

1

1 1

3

1 1 35 18 3

14

24

1 35 18 1 2 1

2

6

1 2 3 6

6 10

1

6

1

1

1

1

6

6

2 1

2 1

1

1 12 1 15

2

1 12 1 15 1 1

1 1

8 1 1 2 1 1 2 3 10 8 1

1

1

8 1 1 2 1 1 2 3 10 9 1

1 11 6

1 3

2 2

1 1

3

1

1 6

6 1

3

21

2 3 12 21

12 9

15 9

1 1

4

2

1

1 4

1

4

2

2

9 1 1 15

1 1

2 1

1 4

1

22 20 1 2 1

22 6 20 1 2 1

3 4

3 4

6 1

9

4

7 6

1 1

9 6

1 2 2

14 6

4 6 2 3 12

46 14

5 3

4 1

17 9

13 9

13

1 99 29

32 4

205 32

81 15

318 47

Okhotsk + Pacific Total 13 3 1 6 2 1 1 1 1 1 1 1 35 18 3 1 2 9 6 24 1 6 2 2 1 1 1 12 1 15 1 9 1 1 2 1 1 2 3 10 9 1 1 14 6 4 6 2 3 12 21 1 21 9 1 1 9 1 1 15 22 6 22 2 2 1 13 3 4 1 417 70

Table 3 Gastropod families found at sampling stations in the Sea of Okhotsk and Kuril-Kamchatka Trench area; numbers of individuals, species and genera are shown for each family. Sea of Okhotsk (St. 1–7, 11) Family

Individuals (%)

Species

Pacific Ocean (St. 8–10) Genera

Individuals (%)

Species

Genera

Seguenziidae

8 (8.1)

1

1

8 (2.5)

2

2

‘Skeneimorph seguenzioids’

9 (9.1)

3

3

3 (0.9)

3

3

Pseudococculinidae

1 (1.0)

1

1

0 (0.0)

–

–

Eulimidae

1 (1.0)

1

1

2 (0.6)

2

1

Naticidae

12 (12.1)

4

2

86 (27.0)

5

2

Newtoniellidae

1 (1.0)

1

1

0 (0.0)

–

–

Buccinidae

5 (5.1)

4

3

57 (17.9)

15

10

Belomitridae

0 (0.0)

–

–

10 (3.1)

1

1

Muricidae

1 (1.0)

1

1

10 (3.1)

2

1

Cancellariidae

10 (10.1)

2

1

22 (6.9)

3

2

Volutomitridae

0 (0.0)

–

–

3 (0.9)

1

1

Mangeliidae

37 (37.4)

9

7

107 (33.6)

9

5

Cochlespiridae

13 (13.1)

1

1

3 (0.9)

2

1

Pseudomelatomidae

0 (0.0)

–

–

7 (2.2)

2

2

Turridae

1 (1.0)

1

1

0 (0.0)

–

–

99

29

23

318

47

31

Total