Abstract
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 This survey is founded on a database including information both from literature sources and also unpublished data of the authors on all recent species of vesicomyids.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.
Highlights
Vesicomyid bivalves are a consistent component of communities that live in reducing environments such as cold seeps at continental margins [1], hydrothermal vents along mid-ocean ridges [2], or associated with organic remains [3]
The distribution pattern of the genus Vesicomya can be formally defined as a transoceanic, eurybathic distribution with a panthalassic type of range
This remarkably broad distribution of Vesicomya (Subfamily Vesicomyinae) is probably the result of a less specialized nutrition compared to those genera that exclusively occur at sulphide-rich reducing habitats. Those genera (Subfamily Pliocardiinae), which live in symbiosis with sulphide-oxidizing endosymbionts in reducing habitats may be formally divided into four groups, characterized by the following distribution patterns: (1) transoceanic mainly bathyal-abyssal distribution with nearcontinental range type: Archivesica, Callogonia, Calyptogena, Isorropodon, Waisiuconcha, Wareniconcha, (2) transoceanic bathyalabyssal distribution with panthalassic range type: Abyssogena, Phreagena, Pliocardia, Laubiericoncha, (3) regional mainly upperbathyal distribution with near-continental range type: Akebiconcha, Ectenagena, Elenaconcha, and (4) regional low bathyal-upper abyssal distribution with oceanic range type: ‘‘C.’’ magnifica
Summary
Vesicomyid bivalves are a consistent component of communities that live in reducing environments such as cold seeps at continental margins [1], hydrothermal vents along mid-ocean ridges [2], or associated with organic remains [3]. Vesicomyids from sulphide-rich reducing environments are rather large, mostly several cm to more than 30 cm in size All of these ‘‘large’’ vesicomyid clams studied so far live in symbiosis with sulphuroxidizing bacteria in their gills [4]. In contrast to the ‘‘large’’ vesicomyids, much less is known about the smaller representatives of the family, belonging to species of the type genus of the family - Vesicomya Dall, 1886, typified by Vesicomya atlantica (Smith, 1885). This genus mostly occurs in deep-sea oceanic basins and trenches. Vesicomyids may be considered as a model taxon in order to study adaptation strategies towards a chemosynthesis-based nutrition
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