`Pliocardia' krylovata, a new species of vesicomyid clam from cold seeps along the Costa Rica Margin

`Pliocardia' krylovata, sp. nov. (Bivalvia: Vesicomyidae: Pliocardiinae) is described from cold seeps off the coast of the Nicoya Peninsula, Costa Rica (700-1000 m depth). The phylogenetic position of `P.' krylovata was assessed by both morphological comparisons as well as nucleotide data from the cytochrome c oxidase I gene. Within the vesicomyids, `P.' krylovata belongs to the Pliocardiinae and its closest relative is `Calyptogena' ponderosa, which also bears some morphological resemblance to the genus Pliocardia, perhaps suggesting a need for reanalysis of not only its generic designation, but also the entire Pliocardiinae subfamily. `P.' krylovata has morphological similarities to `Pliocardia' bowdeniana and `Vesicomya' crenulomarginata, recently reassigned to the genus Pliocardia, including a thick shell, obvious rostrum, pointed posterior end, and a sculptured shell with concentric ribs on the outer surface, to name a few. It is morphologically distinguished, however, by having a complex pallial sinus and remarkably deep escutcheon.