Riftia pachyptila, new genus, new species, is described from geothermal vents of the Galapagos Rift and from a geothermal area on the East Pacific Rise at 21 oN. These vestimentiferan worms represent a new family, Riftiidae, in a new subphylum, Obturata, in the phylum Pogonophora. Differentiation from the two other vestimentiferan species is at the familial level and concerns the orientation of tentacular lamellae on the obturaculum, the number of openings of excretory ducts, and the relative lengths of certain body regions. A most curious structure, the trophosome, occupies much of the trunk region and is essentially a vascularized, bacteria filled sac; it is also the site of deposition of crystals of elemental sulfur.
