Elena M Krylova

Vesicomyidae (Bivalvia): Current Taxonomy and Distribution

Vesicomyid bivalves are a consistent component of communities of sulphide-rich reducing environments distributed worldwide from 77° N to 70°S at depths from 100 to 9050 m. Up-to-now the taxonomy of the family has been uncertain. In this paper, the current state of vesicomyid taxonomy and distribution at the generic rank are considered. This survey is founded on a database including information both from literature sources and also unpublished data of the authors on all recent species of vesicomyids. We suggest that the Vesicomyidae is not a synonym of Kelliellidae, and is therefore a valid family name. We propose to divide the family Vesicomyidae into two subfamilies: Vesicomyinae and Pliocardiinae. The Vesicomyinae includes one genus, Vesicomya, which comprises small-sized bivalves characterized by non-reduced gut and the absence of subfilamental tissue in gills. Symbiosis with chemoautotrophic bacteria has, so far, not been proved for Vesicomya and the genus is not restricted to sulphide-rich reducing habitats. The subfamily Pliocardiinae currently contains about 15 genera with mostly medium or large body size, characterized by the presence of subfilamental tissue in the gills. The Pliocardiinae are highly specialized for sulphide-rich reducing environments, harbouring chemoautrophic bacteria in their gills. This is the first summary of the generic structure of the family Vesicomyidae that allow us to analyze the distribution of vesicomyids at the generic level. We recognize here five different distribution patterns that are related to the specific environmental demands. The general trends in the distribution patterns of the vesicomyids are an occurrence of the majority of genera in broad geographical ranges and the prevalence of near continental type of distribution.

Methane seep community of the Håkon Mosby mud volcano (the Norwegian Sea): composition and trophic aspects

The Håkon Mosby mud volcano (the Norwegian Sea, depth c. 1250 m) was studied in July 1998 by a joint Russian–German–USA–Norwegian expedition on the 40th cruise of the RV Akademik Mstislav Keldysh using the two Mir submersibles. The benthic community is dominated by two species of symbiotrophic pogonophores, Sclerolinum contortum (more abundant) and Oligobrachia haakonmosbiensis. The biomass of S. contortum reaches at least 435 g m ; for O. haakonmosbiensis the value is 350 g m . Different benthic organisms form associations with each species of pogonophore. The total list of known benthic fauna includes 46 species. A zoarcid fish, Lycodes squamiventer, is a common member of the benthic community. Bacterial mats are found over an extensive part of the crater. The background benthic community is much poorer and is dominated by ophiuroids (Ophiocten gracilis, Ophiopleura borealis). Pycnogonids (Collossendeis proboscidea), buccinid gastropods and asteroids are also present. Stable carbon isotope data showed significant depletion of C in both species of pogonophores: in S. contortum δ C was up to −48.3‰, in O. haakonmosbiensis the value varied from −51.1 to −56.1‰. It can be suggested that the methane carbon contributes to the nutrition of the pogonophoran O. haakonmosbisensis. Carbon isotopes also revealed incorporation of non‐photosynthetic carbon into local trophic webs: δ C in Metacaprella horrida (amphipod) showed −44.9‰, in the tube‐dwelling polychaete (Amphinomidae) −40.6‰. In the bacterial mat δ C varied from −17.6 to −53.0.

A new species of Calyptogena (Bivalvia:Vesicomyidae) from a recently discovered methane seepage area off Concepción Bay, Chile (∼36°S)

Calyptogena gallardoi sp. nov. is described from eight articulated and 15 separated valves collected by dredge at ∼760 m depth off the Bay of Concepcion, central Chile (∼36°S). In general outline, C. gallardoi sp. nov. is close to C. pacifica and to a new species of Calyptogena from Peru, from which it differs in details of the shell shape and hinge margin. Bivalves of the genus Calyptogena are typical constituents of marine chemosynthesis-based communities, and are therefore indicators of reducing environments. In the area of occurrence, the presence of C. gallardoi sp. nov. is related to methane seepage, associated in turn with the extensive gas–hydrate fields recently reported for the Chilean margin along 35°S to 45°S. Gas-saturated sediments as well as fragments of other chemosynthetic endosymbiont-containing clams of the families Vesicomyidae, Lucinidae, Thyasiridae and Solemyidae were also retrieved in the area. Calyptogena gallardoi sp. nov. is the first species of Calyptogena s.s. and the second species of the family Vesicomyidae so far described for the south-eastern Pacific area.

Molecular taxonomy reveals broad trans-oceanic distributions and high species diversity of deep-sea clams (Bivalvia: Vesicomyidae: Pliocardiinae) in chemosynthetic environments

Large vesicomyid clams are common inhabitants of sulphidic deep-sea habitats such as hydrothermal vents, hydrocarbon seeps and whale-falls. Yet, the species- and genus-level taxonomy of these diverse clams has been unstable due to insufficiencies in sampling and absence of detailed taxonomic studies that would consistently compare molecular and morphological characters. To clarify uncertainties about species-level assignments, we examined DNA sequences from mitochondrial cytochrome-c-oxidase subunit I (COI) in conjunction with morphological characters. New and published COI sequences were used to create a molecular database for 44 unique evolutionary lineages corresponding to species. Overall, the congruence between molecular and morphological characters was good. Several discrepancies due to synonymous species designations were recognized, and acceptable species names were rectified with published COI sequences in cases where morphological specimens were available. We identified seven species with trans-Pacific distributions, and two species with Indo-Pacific distributions. Presently, 27 species have only been documented from one region, which might reflect limited ranges, or insufficient geographical sampling. Vesicomyids exhibit the greatest species diversity along the northwest Pacific ridge systems and in the eastern Pacific, along the western America margin, where depth zonation typically results in segregation of closely related species. The broad distributions of several vesicomyid species suggest that their required chemosynthetic habitats might be more common than previously recognized and occur along most continental margins.

A new genus of large Vesicomyidae (Mollusca, Bivalvia, Vesicomyidae, Pliocardiinae) from the Congo margin, with the first record of the subfamily Pliocardiinae in the Bay of Biscay (northeastern Atlantic)

Krylova E. M. & Cosel R. von 2011. — A new genus of large Vesicomyidae (Mollusca, Bivalvia, Vesicomyidae, Pliocardiinae) from the Congo margin, with the first record of the subfamily Pliocardiinae in the Bay of Biscay (northeastern Atlantic). Zoosystema 33 (1): 83-99. ABSTRACT A new genus in the subfamily Pliocardiinae (Vesicomyidae), Christineconcha n. gen., is established for “Calyptogena” regab Cosel & Olu, 2009. The most characteristic features of Christineconcha n. gen. are a rather thin and elongate shell up to 122 mm in length, a pallial line starting from the ventral margin of the anterior adductor scar, the presence of the inner demibranch only and the absence of the pallial fusion between the pedal gape and the inhalent siphon. Morphologically, Christineconcha is closest to the genus Abyssogena Krylova & Sahling, 2010. The monospecific new genus occurs in the Atlantic on the continental margin of Africa and Europe, from the Gulf of Guinea to the southern Bay of Biscay, at depths of 2820–4017 m. In the Gulf of Guinea, Christineconcha n. gen. is recorded from cold seeps; in the Bay of Biscay, the record of C. regab n. comb, indicates the likely presence of reducing biotopes. Morphological basis for the slightly different ecological niches of the co-occurring species Christineconcha regab n. comb. and Laubiericoncha chuni (Thiele & Jaeckel, 1931) is discussed.

Phylogeny and origins of chemosynthetic vesicomyid clams

Large vesicomyid clams (Veneroida: Vesicomyidae: Pliocardiinae) are prominent members of the communities associated with sulphide-rich deep-sea habitats. Taxonomic uncertainties within the Pliocardiinae result from both plasticity in shell morphologies and the common occurrence of cryptic species. Molecular taxonomic studies have now clarified many species-level assignments and provided DNA-barcodes for more than 50 species worldwide. Nonetheless, genus-level assignments remain uncertain, because the existing COI barcode sequences are not sufficient for identifying higher-level groupings. To construct a robust phylogeny for this subfamily, we conducted a combined Bayesian analysis of the COI mitochondrial fragment and five additional independent nuclear gene segments. The phylogenetic results provide a better foundation for assessing genus-level assignments within the subfamily and reveal goals for future taxonomic research. Furthermore, morphological examinations helped to clarify and solidify generic classifications. Calibration of molecular clocks with recently verified fossil data permitted realistic estimates for the origins and evolutionary age of pliocardiins during the Cenozoic Era from a deep-dwelling ancestor. http://zoobank.org/urn:lsid:zoobank.org:pub:2554122D-96D4-4CBF-BC70-B017998AF64D

Austrogena: a new genus of chemosymbiotic bivalves (Bivalvia; Vesicomyidae; Pliocardiinae) from the oxygen minimum zone off central Chile described through morphological and molecular analyses

A new genus, Austrogena, is established for a new species of vesicomyid bivalve (A. nerudai sp. nov.) described from sediments within the oxygen minimum zone off El Quisco, Chilean margin (∼33°S) from ∼340 m depth. The new genus is distinguished by a unique combination of conchological and anatomical features for vesicomyids, including the presence of an escutcheon, a lunular incision, an elongated 4-b tooth in the left valve, a subumbonal pit, both inner and outer pairs of demibranchs and the absence of pallial sinus and processes on the inner vulva of the inhalant siphon. In comparison with the majority of highly specialized pliocardiins, the alimentary gut of Austrogena is not straight and its middle gut changes direction twice. Molecular analysis, based on COI sequences, confirms that A. nerudai sp. nov. is not related to any other pliocardiin. So far, Austrogena gen. nov. is the only endemic vesicomyid genus in the south-eastern Pacific area and A. nerudai sp. nov. is the fourth species of vesicomyids reported from chemosynthetic communities of the Chilean margin. The description of the new genus further contributes to knowledge of biodiversity of chemosymbiotic assemblages in the south-eastern Pacific. http://zoobank.org/urn:lsid:zoobank.org:pub:476A9734-B510-4954-A623-2C0E1F254F9A.

Resolving the status of the families Vesicomyidae and Kelliellidae (Bivalvia: Venerida), with notes on their ecology

The bivalve family Vesicomyidae comprises two subfamilies: Pliocardiinae and Vesicomyinae. The Pliocardiinae include conspicuous mostly largeand medium-sized clams, which live in symbiosis with chemoautotrophic bacteria and often dominate chemosynthetic communities in the deep sea. The Vesicomyinae comprise poorly-studied tiny bivalves, which at first sight differ considerably from their better known, large-sized relatives. Vesicomyines have a worldwide distribution from mid-slope to hadal depths and reach abundances of thousands of specimens in one trawl catch in deep-sea trenches. The genus Vesicomya is morphologically very similar to the genus Kelliella, the type genus of family Kelliellidae. This fact has long caused taxonomic ambiguities and it has been suggested that Vesicomya and Kelliella, as well as their respective nominate families, should be synonymized. In this paper we study the relationship between Vesicomya and Kelliella, for the first time using not only morphological characters but also genetic divergence based on the mitochondrial cytochrome c oxidase subunit I (COI) gene. Our molecular data indicate that the genera Vesicomya and Kelliella are clearly distinct and that Kelliella is distantly related to the Vesicomyidae. Results of morphological analysis support the molecular inferences. We provide further evidence for the relationship of vesicomyines and pliocardiines and propose an evolutionary scenario according to which Vesicomyinae is the less derived group and Pliocardiinae the more derived. We provide the first information on stable carbon and nitrogen isotopic composition of soft tissues of Vesicomya and Kelliella. These data do not suggest involvement of chemosynthetically fixed carbon in the nutrition of either Vesicomya or Kelliella. We revise current usage of these two genera and provide lists of the species of each, with details of their distribution. A new species, Vesicomya alleni, is described on the basis of morphological and molecular characters.