Several unknown animal forms have recently been collected in the immediate vicinity of hot hydrothermal vents in the Eastern Pacific Ocean, forming a flourishing community of organisms. A tubicolous polychaete builds parchment-like tubes around some of the hydrothermal vents. The tubes are covered with particles of metallic sulfur. This annelid is a new species, and is called Alvinella pompejana , new genus and species. The new subfamily Alvinellinae, erected to contain this new species, can be included in the family Ampharetidae (order Terebellida), in spite of several aberrant features. In addition to its morphological and taxonomic peculiarities, A. pompejana also exhibits some remarkable biological features, in particular the existence of two successive ontogenetic states. The youngest may ensure species propagation by accidental or normal autotomy.