A new species of bathymodioline mussel (Mollusca, Bivalvia, Mytilidae) from Mauritania (West Africa), with comments on the genus Bathymodiolus Kenk & Wilson, 1985

Bathymodiolus mauritanicus n. sp., taken by commercial trawler at about 1000 m off Banc d’Arguin, northern Mauritania, is described and placed in the context of the genus Bathymodiolus Kenk & Wilson, 1985. No cold seep or hydrocarbon seep has yet been discovered in this region, although the repeated appearance of other mollusc groups typical for this kind of biotope suggests their existence. The new species belongs to a rather uniform and well-defined group of four species of bathymodioline mussels, informally designated as the Bathymodiolus childressi group, which differs from typical Bathymodiolus in a number of shell and soft part characters, specifically a multibundle posterior retractor, almost terminal umbones and the attachment of the anterior retractor to the posterior part of the umbonal cavity. An attempt is also made to reevaluate most of the other species of Bathymodiolus, which results in four groups: 1) the B. thermophilus group (one species, eastern Pacific only: Galapagos, East Pacific Rise); 2) the B. brevior group (five species, Atlantic: Mid-Atlantic Ridge, West Pacific, Indian Ocean); 3) the B. heckerae group (two species, Atlantic); and 4) the B. childressi group (four species, Atlantic, West Pacific).