The Thyasiridae is one of the most species-rich families of bivalves in the deep-sea areas of the northern Pacific Ocean. Many thyasirid species form abundant populations in these regions and play an ...important role in the functioning of deep-sea benthic communities. However, most of these deep-sea thyasirid species have not been identified and many of them are new to science. Based on the material of bivalves collected by eight deep-sea expeditions in the northern Pacific Ocean during the period from 1954 to 2016, three new species of the genus
(
sp. nov.,
sp. nov., and
sp. nov.) are described from the Kuril-Kamchatka and Japan trenches, the Bering Sea, and other deep-water regions of the northern Pacific Ocean (3,200-9,583 m depth). The new species are distinguished due to a unique and complex sculpture of the prodissoconch, including tubercles and numerous thin folds of varying length and shape, as well as due to a thickening of the shell in the adductor scar areas, thus rendering the scars raised above the inner surface of the shell. Comparisons with all species of the genus
are provided.
The Thyasiridae is one of the species-richest families in the abyssal and hadal zones of the northwestern Pacific Ocean. Many thyasirid species dominate benthic communities in terms of abundance and ...play an important role in the functioning of deep-sea ecosystems. Most of the thyasirid species in the region are new to science and have not been described. Based on the material collected from 1954 to 2016 by seven deep-sea expeditions, three new species of Thyasiridae (Parathyasira coani sp. nov., P. pauli sp. nov., and Thyasira kharkovensis sp. nov.) are described from the abyssal and hadal zones (3210–7540 m depth) of the Sea of Okhotsk, the Bering Sea, as well as the Kuril-Kamchatka and Japan trenches. The new species are remarkable among their congeners due to the combination of the following characters: an obliquely-rhomboidal shell with a weak and shallow posterior sulcus and a large prodissoconch with sculpture of lamellated folds. Comparisons with related species are provided.
The Thyasiridae is the most species-rich family of bivalves in the abyssal and hadal zones of the northwestern Pacific Ocean. In recent years, with at least 14 thyasirid species found in that region ...at depths exceeding 3,000 m. Some of them are the numerically dominant species in bottom communities. However, all members in that family have not yet been identified to the species level. Based on the material collected from 1953 to 2016 by five deep-sea expeditions, three new species of Thyasiridae (Mollusca: Bivalvia) are described from the abyssal and hadal zones of the northwestern Pacific. "Axinulus" roseus sp. nov. was found in the Kuril-Kamchatka Trench at 9,000-9,583 m depth. This species has a large rhomboidal shell with strong commarginal sculpture, a well defined, long and deep lunule and escutcheon without an auricle, a ctenidium consisting of a single demibranch, extensively lobed lateral pouches, and a large prodissoconch with specific sculpture. It is one of the dominant species in terms of abundance in macrobenthic communities in the deepest basin of the Kuril-Kamchatka Trench with a population density of up to 396 ind. m.sup.-2 . The species has a shell length of up to 9.0 mm and it is the largest thyasirid with a single demibranch. "Axinulus" oliveri sp. nov. was found in a vast region of the northwestern Pacific on the abyssal plain adjacent to the Kuril-Kamchatka Trench, on the abyssal slope of the Kuril Islands, and in the Kuril-Kamchatka Trench at 4,648-6,168 m depth. This species is characterized by its ovate-rhomboidal shell, a well defined, deep and long escutcheon with a distinct auricle, a ctenidium with a single demibranch, and extensively lobed lateral pouches. It is widespread in the northwestern Pacific and forms populations with a density of up to 36 ind. m.sup.-2 . Scanning electron microscopic observation of the gills of "A." roseus sp. nov. and "A." oliveri sp. nov. revealed that these species are not chemosymbiotic. "Axinulus" roseus sp. nov. and "A." oliveri sp. nov. are provisionally assigned to the genus Axinulus, because they differ from the type species of the genus in a number of morphological and anatomical features. Parathyasira fragilis sp. nov. was found on the abyssal plain adjacent to the Kuril-Kamchatka Trench at 5,249-5,399 m depth. This species is distinguished by its very thin, fragile, dorsoventrally elongated, rhomboidal shell with very long anterodorsal margin and a long, wide, flat lunule. The taxonomic position of the new species is discussed.
Three new species, Hyalopecten vityazi sp. nov., H. abyssalis sp. nov. and H. kurilensis sp. nov., are described from the abyssal and hadal zones of the North-western Pacific. Hyalopecten vityazi was ...found in the Kuril-Kamchatka and Aleutian trenches at 6090–8100 m depth. It is the most deep-water species of the order Pectinida. Hyalopecten abyssalis and H. kurilensis were found at the abyssal plain adjacent to the Kuril-Kamchatka and Aleutian trenches at 4550–5045 m depth. To date, 13 species of the genus Hyalopecten are known from different regions of the World Ocean. A table with the main differences among all known species in the genus is provided.
Based on the material collected from 1949 to 2015 by nine deep-sea expeditions, four new species of the family Propeamussiidae (Mollusca: Bivalvia) and
Catillopecten squamiformis
(Bernard, 1978) were ...found in the abyssal zone (2,901-5,680 m depths) of the Bering Sea, the Sea of Okhotsk, and the northwestern Pacific.
Parvamussium pacificum
sp. nov.,
Catillopecten brandtae
sp. nov.,
Catillopecten malyutinae
sp. nov., and
Catillopecten natalyae
sp. nov. are described from the abyssal plain (4,860-5,680 m depths) adjacent to the Kuril-Kamchatka and Japan trenches (Pacific Ocean).
Catillopecten squamiformis
was found in the Bering Sea, the Sea of Okhotsk, and at the abyssal plain near the southeastern coast of Kamchatka and Aleutian Trench (Pacific Ocean) at 2,901-5,020 m depth. This is the first record of
C. squamiformis
from the northwestern Pacific. An expanded description of
C. squamiformis
with new data on its morphology and geographic distribution is given. To date, 12 species of the genus
Catillopecten
are known from the different regions of the World Ocean. A table with the main differences among all known species in the genus is provided.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Twenty-six bivalve species collected by four Russian (1972, 1976, 1985, 2005) and Russian–German (2010) expeditions in the bathyal and abyssal depths of the Sea of Japan (465–3435m) are listed with ...the material examined and illustrated. Taxonomic decisions herein: Robaia habei Scarlato, 1981 is synonymized with Nuculana (Robaia) robai (Kuroda, 1929); following Scarlato (1981) and Coan et al. (2000)Dacrydium nipponicum Okutani, 1975 and Dacrydium minimum Okutani and Izumidate, 1992 are synonymized with Dacrydium vitreum (Möller, 1842); Maorithyas yamatotaensis Okutani and Izumidate, 1992 is synonymized with Adontorhina cyclia Berry, 1947; Axinopsida rubiginosa Okutani and Izumidate, 1992 is synonymized with Mendicula ferruginosa (Forbes, 1844); Cardiomya lindbergi batialis Scarlato, 1972 is synonymized with Cardiomya tosaensis (Kuroda, 1948); Cuspidaria sadoensis Okutani and Ito, 1983 is synonymized with Cuspidaria ascoldica Scarlato, 1972; Cyclocardia rjabininae (Scarlato, 1955) recognized as valid and distinct from Cyclocardia ovata (Rjabinina, 1952). The deep-water bivalve fauna of the Sea of Japan is characterized by an impoverished shelf fauna and consists of eurybathic species that extend from the shelf to the bathyal and abyssal zones. Most of them have a wide geographic distribution and inhabit cold water regions of the Northern Atlantic, Northern Pacific, and Arctic Ocean. Only five species are endemic to the Sea of Japan. With increase in depth, the species richness of bivalves decreases. In the depth range from 200 to 1600m, all species (26) found in the deep Sea of Japan were recorded, while only 10 species were recorded in the lower bathyal slope (1700–3000m). At depths below 3000m, only D. vitreum, Delectopecten vancouverensis (Whiteaves, 1893), and Thyasira (Parathyasira) sp. were found. The lack of typical abyssal species of bivalves in the deep Sea of Japan is probably connected with the isolation of this body of water from the Pacific abyssal depths.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Previous studies have deciphered the genomic basis of host-symbiont metabolic complementarity in vestimentiferans, bathymodioline mussels, vesicomyid clams and Alviniconcha snails, yet little is ...known about the chemosynthetic symbiosis in Thyasiridae-a family of Bivalvia regarded as an excellent model in chemosymbiosis research due to their wide distribution in both deep-sea and shallow-water habitats. We report the first circular thyasirid symbiont genome, named Candidatus Ruthturnera sp. Tsphm01, with a size of 1.53 Mb, 1521 coding genes and 100% completeness. Compared to its free-living relatives, Ca. Ruthturnera sp. Tsphm01 genome is reduced, lacking components for chemotaxis, citric acid cycle and de novo biosynthesis of small molecules (e.g. amino acids and cofactors), indicating it is likely an obligate intracellular symbiont. Nevertheless, the symbiont retains complete genomic components of sulphur oxidation and assimilation of inorganic carbon, and these systems were highly and actively expressed. Moreover, the symbiont appears well-adapted to anoxic environment, including capable of anaerobic respiration (i.e. reductions of DMSO and nitrate) and possession of a low oxygen-adapted type of cytochrome c oxidase. Analysis of the host transcriptome revealed its metabolic complementarity to the incomplete metabolic pathways of the symbiont and the acquisition of nutrients from the symbiont via phagocytosis and exosome. By providing the first complete genome of reduced size in a thyasirid symbiont, this study enhances our understanding of the diversity of symbiosis that has enabled bivalves to thrive in chemosynthetic habitats. The resources will be widely used in phylogenetic, geographic and evolutionary studies of chemosynthetic bacteria and bivalves.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•Thirty-three bivalve species were found in the hadal of the Kuril-Kamchatka Trench.•Fourteen species were first records for the Kuril-Kamchatka Trench.•Five species were found at the maximum depth ...of the trench (over 9500 m).•Fourteen species (identified species and morphospecies) (42.4%) are endemic to the hadal of the Kuril-Kamchatka Trench.•The depth range of 6000–6999 m is a transitional zone between the abyssal and hadal.
The Kuril-Kamchatka Trench with a maximum depth of 9600 m is one of the deepest trenches of the World Ocean and has the second (to the Izu-Bonin Trench) largest area of hadal habitat. Investigation of the materials collected by the KuramBio II German-Russian expedition (RV Sonne, 2016) (8 stations), and three Russian expeditions (RV Vityaz, 1949, 1953, 1966) (16 stations) from the hadal zone of the Kuril-Kamchatka Trench (6000–9583 m depth) revealed a rich fauna of bivalves including 33 species (identified species and morphospecies) belonging to 15 families, of which 18 species (54.0%) were determined to the species level and 14 species (42.4%) were first recorded for the Kuril-Kamchatka Trench. Of the 33 species found in the Kuril-Kamchatka Trench, 15 species (45.5%) were recorded outside the trench at depths of less than 6000 m. Vesicomya sergeevi Filatova, 1971 and Parayoldiella ultraabyssalis (Filatova, 1971) formed the most abundant populations in the trench (72.9% of all specimens of bivalves collected by the KuramBio II expedition) and were predominant in samples from the trench bottom. In the hadal zone of the Kuril-Kamchatka Trench, 3 depth ranges (6000–6999, 7000–8999, 9000–9583 m) were distinguished that differ in the species composition of bivalves. The bivalve fauna of the upper hadal zone of the Kuril-Kamchatka Trench (depths 6000–6999 m) is characterized by the highest species richness (23 species) and is represented mainly (65.2%) by bathyal-hadal and abyssal-hadal species. This depth range is considered as a zone of transition between the abyssal and hadal zones. The fauna of this transitional zone is most closely connected with the fauna of the abyssal plain adjacent to the trench. At depths of more than 7000 m, the proportion of hadal endemics significantly increases (more than 66%). At the maximum depth of the trench (over 9500 m), only 5 species were recorded. Of the 18 identified species, only 6 species (33.3%) were found exclusively in the hadal zone of the trench. Photographs, taxonomic remarks and distribution are provided for all identified species that were found in the hadal zone of the Kuril-Kamchatka Trench. Taxonomic decisions herein: Bathyspinula vityazi (Filatova, 1964) is a distinct species and not a synonym of Bathyspinula calcarella (Dall, 1908); Ledella spinuliformis F. R. Bernard, 1989 is synonymized with Ledellina formabile Filatova and Schileyko, 1984; following Krylova (1993) Myonera demistrata Allen and Morgan, 1981 is considered as a synonym of Bathyneaera hadalis (Knudsen, 1970).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
SokhoBio expedition Until recently hardly anything was known about the abyssal bivalve fauna of the Sea of Okhotsk, which communicates with the Pacific Ocean via many straits between the Kuril ...Islands with a maximum depth of 2318m in Bussol Strait, and about its similarity with the deep-water fauna of the Pacific. Investigation of the materials collected by the SokhoBio Russian-German deep-sea expedition (RV “Akademik M.A. Lavrentyev”, 2015), and two Russian expeditions (RV “Toporok”, 1948; RV “Vityaz”, 1949) from the bottom of the Kuril Basin of the Sea of Okhotsk (2850–3366m depth) revealed a rich fauna of bivalves including 25 species belonging to 12 families, of which only 12 species (48.0%) were determined to the species level. Nine species (Poroleda extenuata, Katadesmia vincula, Dacrydium rostriferum, Bathyarca imitata, Catillopecten squamiformis, Channelaxinus excavata, Vesicomya pacifica, Cuspidaria cf. abyssopacifica, Myonera garretti) were first records for the Sea of Okhotsk. The richest families were Thyasiridae (7 species) and Cuspidariidae (6 species). The high diversity and richness of the bivalve fauna on the bottom of the Kuril Basin are probably caused by the favorable trophic conditions. The Kuril Basin is characterized by very high rates of sedimentation and high content of organic matter in the sediments. For estimation of connections between deep-water faunas of the Sea of Okhotsk and the Pacific Ocean, the SokhoBio expedition performed 1 station at the maximum depth of the Bussol Strait and 2 stations (3342–3432 and 4679–5013m) on the Pacific slope of the Kuril Islands opposite to the Bussol Strait, where 24 species belonging to 13 families were found. Among the 25 species found in the deep part of the Kuril Basin more than half of species (17 species, 68%) occur in the Pacific Ocean. Most of them are widespread in the northern Pacific and are eurybathic bathyal-abyssal species. This probably allows them to penetrate into the Sea of Okhotsk through deep straits between the Kuril Islands. Photographs and taxonomic remarks are provided for all identified species (15) that were found in the Sea of Okhotsk and/or the Pacific Ocean. Taxonomic decisions herein: Nuculana aikawai Habe, 1958 and Nuculana sagamiensis Okutani, 1962 are synonymized with Nuculana leonina (Dall, 1896); Arca (Bathyarca) nucleator Dall, 1908 is synonymized with Bathyarca imitata (Smith, 1885); for Leda extenuata Dall, 1897, a new combination is suggested, Poroleda extenuata (Dall, 1897).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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