The family Lyonsiellidae Dall, 1895, distributed worldwide from sublittoral to ultra-abyssal zone, presently comprises four genera of carnivorous bivalves: Lyonsiella Friele, 1879, Policordia D & acy;ll, Bartsch et Rehder, 1938, Allogramma Dall, 1903, and Dallicordia Scarlato et Starobogatov, 1983 (the last with a dubious taxonomic position). Angustebranchia Ivanova, 1977 was proposed as a subgenus of Policordia based on the description of four ultra-abyssal species from the Kuril-Kamchatka Trench. Elevated to the genus level, Angustebranchia was later on synonymized with Policordia. Here we reinstate Angustebranchia as a genus based on new morphological and molecular data. We present previously unknown anatomical data of P. diomedea D & acy;ll, Bartsch et Rehder, 1938, the type species of Policordia. Morphologically, Angustebranchia differs from Policordia, Lyonsiella and Allogramma by the shell sculpture, arrangement of the siphonal tentacles and the mouth shape. For the first time, molecular data for 16S and 18S rRNA gene fragments were obtained for two Angustebranchia species including the type species, A. rectangulata Ivanova, 1977, and for an undescribed Policordia species. We sequenced DNA of the type material of A. rectangulata collected 60 years ago. Monophyly of the family Lyonsiellidae in current understanding is not confirmed. Data on 16S and 18S support sister relationship of Angustebranchia and Policordia. The two genera show different patterns of bathymetric distribution: eurybathic Policordia is distributed from the sublittoral to the upper ultra-abyssal zone (44-6040 m) while Angustebranchia is limited to the ultra-abyssal zone (8160-9583 m). Angustebranchia increases the group of ultra-abyssal endemic Bivalvia genera, previously comprising only Parayoldiella Filatova, 1971, Ptilomyax Oliver, 2012, and Tartarothyasira Oliver & Chen, 2024.

For the first time carnivorous bivalve mollusc Cuspidaria trosaetes Dall, 1925 was recorded in the north-western Sea of Japan. There was only one species of Cuspidaria, C. ascoldica, previously known in this region. Alive specimens of C. trosaetes were collected in the Tatarsky Strait on the continental slope on muddy sediment at the depths of 531–589 m. Stomach contents of C. trosaetes consist of foraminifers, copepods and rissoid gastropods. Cuspidaria trosaetes was selected as a type species of a monotypic subgenus C. (Nordoneaera) Okutani, 1985, which is now considered a separate genus, based on the presence of a thick shell without sculpture and with thick periostracum, as well as a short rostrum. The first obtained data on anatomy of C. trosaetes suggest its close affinity with the type species of the genus Cuspidaria, C. cuspidata. Cuspidaria trosaetes and C. cuspidata share such features as the presence of 5 pairs of septal pores, thin elongated posterior labial palps and the presence of two rows of papillae on the rim of the common siphonal sheath. Taking into account new data we propose to synonymize the monotypic genus Nordoneaera with the genus Cuspidaria.

For the first time carnivorous bivalve mollusc Cuspidaria trosaetes Dall, 1925 was recorded in the north-western Sea of Japan. There was only one species of Cuspidaria, C. ascoldica, previously known in this region. Alive specimens of C. trosaetes were collected in the Tatarsky Strait on the continental slope on muddy sediment at the depths of 531–589 m. Stomach contents of C. trosaetes consist of foraminifers, copepods and rissoid gastropods. Cuspidaria trosaetes was selected as a type species of a monotypic subgenus C. (Nordoneaera) Okutani, 1985, which is now considered a separate genus, based on the presence of a thick shell without sculpture and with thick periostracum, as well as a short rostrum. The first obtained data on anatomy of C. trosaetes suggest its close affinity with the type species of the genus Cuspidaria, C. cuspidata. Cuspidaria trosaetes and C. cuspidata share such features as the presence of 5 pairs of septal pores, thin elongated posterior labial palps and the presence of two rows of papillae on the rim of the common siphonal sheath. Taking into account new data we propose to synonymize the monotypic genus Nordoneaera with the genus Cuspidaria.

Benthic communities of the hydrothermally active submarine Piip Volcano (55 degrees 445 N, 167 degrees 263 E, 368-495 m, the southwestern Bering Sea) were explored during the 75th and 82nd cruises of the RV Akademik M.A. Lavrentyev using the ROV Comanche 18. The Piip Volcano is the northernmost hydrothermal region in the Pacific. Macrofauna composition and community structure were investigated based on qualitative and relative abundance samples along with still images and video records. In total, 130 species of macro- and megafauna were found, of which similar to 25% are new to science. Of the fauna, 9 species (7%) are obligate or potentially obligate to environments with access to reduced chemicals. These species are the bivalve Calyptogena pacifica (Vesicomyidae: Pliocardiinae), the gastropods Parvaplustrum wareni (Parvaplustridae) and Provanna sp. (Provannidae), the amphipod Onesimoides sp. (Tryphosidae), the leptostracan Nebalia piipensis (Nebaliidae), the isopod Eurycope andreyi (Munnopsidae), and the polychaetes Neosabellides uschakovi (Ampharetidae), Ophryotrocha beringiana (Dorvilleidae) and Harmothoe globosa (Polynoidae). The total species richness of the Northern and Southern summits was almost identical (90 species and 85 spp respectively), but the number of species on sites without bacterial mats on the Northern Summit (81 spp) was almost 1.5 times higher than on the Southern Summit (57 spp). At the same time the species richness was almost twice higher in habitats with bacterial mats and/or clam beds on the Southern Summit (58 spp) compared to the Northern one (32 spp). The main faunal difference was the absence of Calyptogena pacifica on the Northern Summit. The factors that may explain differences of the faunal communities of the Northern and Southern summits are discussed. The distinctive features of macro- and megafaunal communities of the Piip Volcano were the significant number of taxa, obligate for reducing habitats, of different taxonomic levels including family and subfamily levels and plentiful abundances of sedentary organisms, including the sea anemone Corallimorphus cf. pilatus, the demosponge Vulcanella koltuni, calcareous sponges and benthopelagic Trachimedusa, all of them presumably utilizing the rich food resources of reducing habitats.

Methane seep communities on the Koryak slope in the Bering Sea were discovered in 2018 during the 82nd cruise of the RV Akademik M.A. Lavrentyev using ROV Comanche 18. Methane seeps found between 400 m and 695 m depth are the northernmost chemosynthesis-based habitats (similar to 61 degrees N) known to date in the Pacific. Macrofauna species composition and community structure of methane seep and background benthic communities were investigated at three depth horizons: 400-402 m, 417-429 m and 647-695 m. A total of 335 macrofaunal species were identified. At the depth 647-695 m the species richness in the methane seep communities was 265 species and 72 species in the background. The deepest seep communities were characterized by the highest species richness, relatively high evenness and strong variations in the composition and structure. At shallower depths the species richness was low: 33-34 species at methane seeps and 66-71 in the background. The methane seep communities at shallow depths showed relatively low evenness and low diversity of community structure. The highest species richness at the greatest depth can be related in part to increased habitat heterogeneity associated with carbonate crusts and vesicomyid clam beds occurring only at deeper methane seeps. The deepest methane seep communities were dominated by the chemosymbiotrophic pliocardiine Calyptogena pacifica; dominant in the background was the ophiumid Ophiophthalmus normani. At shallower methane seeps only single specimens of C. pacifica were found. The shallower methane seeps were dominated by the background species despite numerous extensive bacterial mats and high potential toxicity of the environment. The seep community at 417-429 m was dominated by the echinoid Brisaster latifrons with population density on the bacterial mat four times higher than in the background. Four chemosymbiotrophic species were recorded at 647-695 m and only one was found at shallower depths. Potentially obligate to reducing habitats polychaetes of the genus Neosabellides and Ophryotrocha occurred in methane seep communities at all depths. Further geochemical, geological and microbiological studies are required to better characterize differences of methane seeps at different depths and reasons of these differences.

Methane seeps are widely distributed in the ocean being represented at all depths and latitudes. Along with hydrocarbons, seeping fluids can supply many chemical elements, including trace metals which benthic communities are needed. Under the condition of climate warming, the methane diffuse flow in the ocean can affect chemical balance. In this study for the first time, in the methane seep ecosystem recently discovered on the Koryak slope of the Bering Sea, we examined the distribution of some essential and potentially toxic chemical elements. In the benthic organisms, biotope water, and surface sediments, concentrations of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Zr, Mo, Cd, Ba, W, Pb, and U were quantified. Dissolved methane in water, total carbon (TC), and total inorganic carbon (TIC) in organisms and sediments, as well as the mineral composition of sediments, were also determined. Our data showed that bioaccumulation of many trace metals in benthic organisms is related to high concentrations of these elements in near-bottom water of methane cold seep habitats. Significantly elevated concentrations of many trace elements, especially chalcophile, were recorded in the gills and to a lesser extent, in the rest of the soft body of chemosymbiothrophic bivalve mollusk Calyptogena pacifica. Together with the essential elements Cu, Zn, Co, Ni, Cr, Mo, and Cd, potentially toxic As, Pb, U, and W also exhibited noticeably higher accumulation in the soft tissues of organisms. In all cases, tissues and whole organisms which are enriched in TOC exhibited higher trace element concentrations and BCF values. Bioconcentration Factor (BCF) exhibited a trend to decrease from the gills of C. pacifica (n106), to whole bodies of suspension feeders (n104). Reducing conditions led to strong depletion in most elements of surface sediments with the enrichment factor (EF) being around 1. Exceptions were Mo and Ba whose EF values (up to 2.2) suggest detectable authigenic enrichment.

On cruise 93 of the R/V Akademik M.A. Lavrentyev (2021), we studied benthic communities in the Gamov Canyon (Sea of Japan), off the eastern coast of Kamchatka, and methane seep communities of the Koryak slope (Bering Sea); in addition, data were obtained on the sea-air mercury flux. The studies confirm the potential of the Gamov Canyon as a model site for long-term monitoring. We document significant changes in the structure and composition of the fauna compared to 2018 in the background and methane seep communities of the Koryak slope.

Five species of deep-sea acorn worms (Enteropneusta) were found in the Bering Sea during cruises of the RV Akademik M.A. Lavrentyev in 2016, 2018, and 2021. The worms were recorded on slopes of the Volcanologists Massif and in the Komandorsky Graben at depths between 1830 and 4278 m and on the Koryak slope between 419 and 662 m. Four of the species were only photographed but not collected; these were an unidentified Torquaratoridae gen. sp. 1 and three harrimaniids: Saxipendium sp., Harrimaniidae gen. sp. 1 and Harrimaniidae gen. sp. 2. Harrimaniidae gen. sp. 1 and gen. sp. 2 were recorded on the Koryak slope in the vicinity of methane seeps. The fifth species was photographed in situ and collected. It has been examined using morphological and molecular methods. It is described in the present study as Quatuoralisia malakhovi n. gen. n. sp. Ezhova et Lukinykh (fam. Torquaratoridae). The abundance of this species in the soft-sediment community at the depth 1830-2290 m was up to 12 specimens per m2, the highest ever recorded for any deep-sea enteropneusts. Morphologically, Q. malakhovi n. gen. n. sp. is noteworthy for the mesocoel ducts, the heart-kidney complex with a pericardial coelom, the two-plated skeleton supporting the proboscis stalk, and conspicuously elongated lateral wings developed on either side of the trunk. The molecular analysis based on the mitochondrial 16S rRNA showed that Q. malakhovi n. gen. n. sp. is closest to several torquaratorid species that have yet to be formally described morphologically.

The Piip Volcano is a submarine volcanic edifice occupying the central part of the Volcanologists Massif in the southwestern Bering Sea, with two tops, southern and northern. The minimum depth of the northern top is located at 368 m, and of the southern at 464 m. Active hydrothermal venting occurring at both summits of the volcano supports diverse biological communities, including animals specific for chemosynthetic habitats. In benthic organisms inhabiting the northern and southern tops of the Piip Volcano, for the first time, we examined distribution patterns of the following trace elements: titanium, vanadium, chromium, manganese, iron, nickel, copper, zinc, arsenic, selenium, zirconium, molybdenum, silver, cadmium, antimony, barium, tungsten, lead, bismuth, and uranium. The element contents were quantified by the ICP-MS. Total carbon (TC) and total inorganic carbon (TIC) were determined using a Shimadzu TOC-L-CPN and mineral composition of sediment was determined using the XRD. In the water of the biotope from the northern top, concentrations of Mn, Zn, Ag, Cd, Sb, W, Pb were 2–6 times, and Ba was 50 times higher than those from the southern top. This was attributed to the lower temperature of fluids emanating at the southern top. An abundant population of Calyptogena pacifica (Bivalvia: Vesicomyidae: Pliocardiinae) was found only at the southern top. The main target of most trace elements, such as Fe, V, Cr, Co, Ni, Zn, As, Mo, Ag, Cd, W, Pb, Bi, and U were the soft parts of Calyptogena pacifica (with high TOC content, on average 53.1% in gills and 49.6% in the rest of the body). Gills were characterized by particular high contents (>100 µg g−1 dry w.) of Zn, Cd, Fe, Ni, Cu, and Pb, which can form sulphides or be associated with them. Shells of C. pacifica, as well as Brachiopoda, were depleted in these elements, as well as tissues of the carnivores Paguridae (Crustacea) and Actiniaria (Anthozoa). In suspension feeders from both tops, the lower contents of most elements were detected. Estimation of Biological Concentration Factor (BCF) for most elements varied from 102 to 104, reaching n105 for Ni, Zn, Ag, Cd, and Pb. A significant difference in BCF values between Fe and Mn was revealed.

Deep-sea hemichordates Torquaratoridae gen. sp. reach high abundance up to 12 spec. m –2 at the depths of 1830–2130 m on the slope of the Volcanologists Massif in the south-western part of the Bering Sea, dominating in the benthic community at these depths. Their abundance exceeds by two orders the values recorded earlier. In order to clarify this phenomenon, we examined the gut contents of Torquaratoridae gen. sp. The detritus particles and frustules of planktonic diatoms Thalassiosira , Coscinodiscus , Actinocyclus , Chaetoceros , Neodenticula, and Grammatophora were the most common in the gut, as well as the remains of skeletons of benthic invertebrates with little admixture of mineral particles. According to obtained data, Torquaratoridae gen. sp. are mobile deposit feeders with high selectivity to fresh phytodetritus, able to compete with holothurians occupying similar trophic niche. Unusually high abundance of acorn worms is apparently related to high organic matter flux to the seafloor as a result of spring phytoplankton bloom in the surface water layer of the Bering Sea.

This is not a regular journal publication and not just «memoirs». These are sketches written by different authors but all about the same person – Lev Ivanovich Moskalev. On the 4th of December 2021 it will a year since Lev Ivanovich has left us. Relatives, friends and colleagues of Lev wrote about him. Everyone in his own way and everyone about his own. In the mosaic of these sketches, various features and sides were captured of Lev Moskalev, the bright person who has left a deep impression on many of his contemporaries.

The family Lyonsiellidae comprises carnivorous bivalve molluscs, distributed worldwide from sublittoral to ultraabyssal depths. One of the key anatomical characters of lyonsiellids is the reduction of the gill filaments in size and number and an increase of amount of muscles and connective tissue in gills, so their ctenidia represent an intermediate stage between eulamellibranch and septibranch conditions. The family Lyonsiellidae presently includes four genera: Lyonsiella, Allogramma, Policordia and Dallicordia. Taxonomy of the family is still problematic at both generic and species levels. The genus Dallicordia, typified by Lyonsiella alaskana was established on the assumption that it has no gills but possesses a muscular septum pierced by ostia, in contrast to the other lyonsiellids that have filamentous gills. Additionally, Lyonsiella uschakovi and Policordia ochotica were tentatively assigned to the new genus. Later P. ochotica was synonymized with P. media. In this paper we show that actually the Dallicordia was typified by an undescribed species misidentified as Lyonsiella alaskana which we describe here as D. bernardi sp. nov. Taxonomic position of the genus is dubious and could be clarified only after additional anatomical data on its type species becomes available. On the basis of examination of the type material of P. ochotica and images of the holotype of P. media, we reinstate the species P. ochotica. For the first time photographs of the holotype of L. uschakovi are provided for this specimen that was previously considered lost. Given the current state of knowledge we propose to consider species L. alaskana, L. uschakovi and P. ochotica in frame of the genus Policordia, for which we provide a list of all 29 species described up to date.

Geothermal energy provides an important resource in Antarctic marine ecosystems, exemplified by the recent discovery of large-sized chemosymbiotic vesicomyid bivalves (subfamily Pliocardiinae) in the Southern Ocean. These clams, which we identified as Archivesica s.l. puertodeseadoi, have been reported as dead shells in areas previously covered by Larsen A and B ice shelves (eastern Antarctic Peninsula) and as live animals from active hydrothermal sites in the Kemp Caldera (South Sandwich Arc) at depths of 852–1487 m. Before, A . puertodeseadoi was known only from its type locality in the Argentine Sea, so we considerably extend the range of the species. Observations taken by remotely operated vehicle (ROV) footage show that the clams can live buried in sediment, or epilithically on the surface of rocks in diffuse geothermal flow. Experimental respirometry was conducted at surface pressure on individual bivalves acclimated to either their habitat temperature (4 °C) or elevated temperature (10 °C). The range of standard metabolic rates, from 3.13 to 6.59 (MO 2 , μmol O 2 h −1 g −1 dry tissue mass), is similar to rates measured ex situ for other species in this clade, and rates did not differ significantly between temperature groups. Taken together, these data indicate a range of ecophysiological flexibility for A. puertodeseadoi . Although adapted to a specialist mode of life, this bivalve exploits a relatively broad range of habitats in the Southern Ocean: within sulphidic sediments, epilithically in the presence of diffuse sulphidic flow, or in deep methane-enriched seawater trapped under ice.

The article is dedicated to the memory of L.I. Moskalev – renowned bio-oceanographer, zoologist who spent his entire scientific career at the Laboratory of Ocean Bottom Fauna. L.I. Moskalev participated in more than 30 deep-sea voyages, spent 200 hours diving in manned submersibles “Pisces” and “Mir”, published about 100 scientific papers and a popular book «Masters of the Deep» (2005). Colleagues will remember Lev Moskalev – an extraordinary and deep person and a true patriot of the Laboratory and P.P. Shirshov Institute of Oceanology

A new monotypic genus, Turneroconcha, is established for T. magnifica (Boss Turner) which was originally assigned to the genus Calyptogena Dall. The distinguishing morphological characters of the new genus are the combination of both conchological and anatomical features including: the presence of only two tooth elements in the right valve; submerged location of the posterior part of the posterior lamellar ligament layer; the absence of a subumbonal pit, lunular incision, escutcheon and pallial sinus; the presence of both pairs of demibranchs; the tubular structure of marginal parts of the interlamellar septa in gills; an inner valve of the inhalant siphon without processes; tentaculate inner mantle fold 3 and a Z-shaped digestive tract. Analysis of morphological data on Recent and fossil pliocardiines shows that Turneroconcha gen. nov. can be presently considered as a monotypic genus. The comparative morphological analysis of the new genus with described pliocardiine genera is consistent with available molecular results. Turneroconcha gen. nov. is endemic to the East-Pacific Rise and Galapagos Rift and occurs at water depths of 2251 to 2791 m. It is the only pliocardiine genus known so far with a mainly epifaunal life habit. No fossils of Turneroconcha gen. nov. are known.

Pliocardiines (Bivalvia: Vesicomyidae: Pliocardiinae) are symbiotrophic vesicomyid molluscs harbouring symbiotic sulphide-oxidizing chemoautotrophic bacteria in their gills. The pliocardiines, Phreagena soyoae and Archivesica gigas, are a common component of numerous deep-sea chemosynthesis-based communities in the Eastern and Western North Pacific. We examined the stable isotope composition of carbon, nitrogen and sulphur as well as the fatty acid composition of P. soyoae and A. gigas from two methane seep sites, Clam Hill (1427 - 1443 m) and Barite Ridge (1455 - 1548 m) in the Deryugin Basin in the Sea of Okhotsk. For identification of bacterial endosymbiont lineages, we determined the nucleotide sequences of CO/ genes of symbionts of P. soyoae and A. gigas and confirmed that both species have the same bacterial lineages as their Eastern Pacific counterpart populations. Stable isotope analysis showed that site-specific differences between pliocardiines from the two seeps of the Deryugin Basin far exceeded interspecies variations. There were obvious differences in the sulphur isotopic compositions among pliocardiines from Clam Hill and from Barite Ridge suggesting that the intensity of anaerobic methane oxidation and methane flow varied in different cold seeps from the Deryugin Basin. The delta C-13 values recorded for P. soyoae and A. gigas samples were in the narrow range typical for studied pliocardiines. Both species showed an unusually broad range of delta N-15 values (similar to 18 parts per thousand) that overlapped the known range of this signature for pliocardiines. The main polyunsaturated fatty acids in P. soyoae and A. gigas were nonmethylene-interrupted 20:2(5,13), 20:3(5,13,16) and 20:4(5,13,16,19), which were synthesized by the molluscs themselves and not by their symbionts.