Calyptogena diagonalis, a new vesicomyid bivalve from subduction zone coldseeps in the eastern North Pacific

A new vesicomyid bivalve species, Calyptogena diagonalis, is described from cold seep communities in the Cascadia subduction zone off the Oregon coast and accretionary wedge sediments along the Pacific coast of Costa Rica. Li ve bivalves and shells were collected at sulfide seeps near 2021 m depth in Oregon and from 2900 to 3800 m depth in Costa Rica. Shell morphology of C. diagonalis differs considerably from sympatric congeneric and confamilial species of the northeastern Pacific. Shells are large (to 24.0 cm) and elon gate (H/L = 0.42), with one or more ridges on the external shell surface ex tending diagonally from the umbo to near the posteroventral margin. Enlarge d, sulfur-colored ctenidia and micrographs of endosymbiotic bacteria held i n ctenidia suggest that this species, like other vesicomyids, is a sulfur-b ased chemolithoautotroph.