The phylogenetic relationships of whale-fall vesicomyid clams based on mitochondrial COI DNA sequences

Whale skeletons on the deep-sea floor provide sulfide-rich habitats that ma y act as stepping stones for the dispersal of animals dependent on chemoaut otrophic production. However, the phylogenetic relationships between the fa unas of whale falls, hydrothermal vents and colds seeps are not fully evalu ated. Tb examine vesicomyid phylogenetic relationships, we collected 10 ves icomyid clams from 2 whale falls on the California margin, one at 1240 m in the Santa Catalina Basin and one at 960 m on the slope west of San Nicolas Island. We then compared DNA sequences for a portion of the mitochondrial cytochrome c oxidase subunit I gene from the whale-skeleton clams to those from other clam populations in this taxonomically difficult family. Seven a dult whale-fall vesicomyids clustered with clams identified as Vesicomya gi gas, a species also found near hydrothermal vents in Guaymas Basin (Gulf of California) and Middle Valley (Juan de Fuca Ridge). A single small whale-f all individual clustered with clams identified as Calyptogena kilmeri, a sp ecies found at cold seeps in Guaymas Basin, Monterey Bay, and along the Ore gon Subduction Zone. A single small whale-fall clam clustered with Calyptog ena elongata, a species found in anoxic California basins. Finally, a singl e adult clam was difficult to assign to any previously examined species gro up and could represent a new species in the 'gigas/kilmeri'' cryptic specie s complex. With the inclusion of these vesicomyids, whale falls are known t o share a total of 16 species with the faunas of deep-sea hydrothermal vent s and cold seeps.