Bathymodiolus (Bivalvia : Mytilidae) from hydrothermal vents on the AzoresTriple Junction and the Logatchev hydrothermal field, Mid-Atlantic Ridge

Bathymodiolus azoricus n. sp. is described from the Lucky Strike (31 degree s 17'N) and the Menez Gwen (37 degrees 50'N) hydrothermal fields on the Azo res Triple Junction, Mid-Atlantic Ridge, and another species, Bathymodiolus sp. aff. B. puteoserpentis from Logatchev (14 degrees 45'N) hydrothermal f ield is treated but not named. Both species are compared with B. puteoserpe ntis Cosel, Metivier & Hashimoto, 1994, from the Snake Pit area (23 degrees 22'N), also on the Mid Atlantic Ridge. B. azoricus is very variable but we ll distinguished from Bathymodiolus sp. and B. puteoserpentis by its almost terminal umbo. The three species differ from the type species B. thermophi lus principally by the absence of an inner mantle fusion and a very short v alvular siphonal membrane. The slight differences between B. puteoserpentis and Bathymodiolus sp. from the Logatchev field do not warrant separation o f the latter on species level. The specific endemism of Mytilidae along the Mid-Atlantic Ridge is discussed.