The giant white calm from the Galapagos Rift, Calyptogena magnifica species novum

During DSRV/ALVIN cruises to the Galapagos Rift and the East Pacific Rise in 1977 and 1979, dense populations of large white clams were found associated with the thermal vents.On the basis of shell characters, M. Keen identified them as a species of Calyptogena, family Vesicomyidae.These clams exceed 260 mm in length and are the largest known living members of this family, though some fossil vesicomyids are comparable in size.Morphologically they closely resemble C. pacifica and C. kilmeri, the only species of Calyptogena which have been studied anatomically.Specimens ranging from 34.5 to 263 mm in length obtained during the 1977 and 1979 cruises are here described as a new species, C. magnifica, most closely related to C. elongata from off the coast of southern California, a species described by Dall on the basis of shells only.In Appendix 1, C. Berg and R. D. Turner describe living specimens, noting the pink-purple iridescences of the mantle, the yellow-brown, wrinkled periostracum, the short siphons which do not extend beyond the valves, and the large iridescent-pink protrusible foot.The red blood pigment, a haemoglobin, gives the visceral mass a red appearance.The gills in large specimens are mottled red-brown with purple lines on the ventral margin while in small specimens they are a uniformly pinkish cream.In Appendix 2, K. Boss provides an annotated checklist of ten fossil and seven living species of Calyptogena.One species is from the eastern Atlantic, off Africa; two are from the western Caribbean and 14 from the eastern and northern Pacific and Peru to Japan.