CALYPTOGENA-PACKARDANA, A NEW SPECIES OF VESICOMYID BIVALVE FROM COLDSEEPS IN MONTEREY BAY, CALIFORNIA

Calyptogena packardana, a new bivalve species of the family Vesicomyid ae, is described from specimens collected from sulfide seeps near 600 m depth in the Monterey Submarine Canyon, Monterey Bay, California. Sh ell characteristics of C. packardana differ considerably from those of sympatric confamilial species (Calyptogena pacifica, C. kilmeri, C. g igas, and Vesicomya stearnsii) found at cold seeps in Monterey Bay and elsewhere in the northeastern Pacific. They are most similar to those of two fossil species (C. gibbera, C. lasia), from Pleistocene and Pl iocene deposits in southern California. The soft anatomy, including ma ntle and siphons, ctenidia, and foot, are discussed. Ratios of stable carbon isotopes near-36 parts per thousand PDB units and presence of e ndosymbiotic bacteria in ctenidial tissues indicate that chemosynthesi s, via thiotrophic chemoautotrophic endosymbiotic bacteria, is the pri mary nutritional source for C. packardana, as reported for other vesic omyids.