The genus Bathyporeia Lindström, 1855, in western Europe (Crustacea: Amphipoda: Pontoporeiidae)

The amphipod genus Bathyporeia Lindström, 1855, on the European Atlantic coasts is revised and new identification keys are provided. The importance of new characters such as the morphology of the first uropod is stressed. The following species are fully redescribed and illustrated: B. elegans Watkin, 1938, B. gracilis G.O. Sars, 1891, B. guilliamsoniana (Bate, 1857), B. nana Toulmond, 1966, B. pelagica (Bate, 1857), B. pilosa Lindström, 1855, B. sarsi Watkin, 1938, and B. tenuipes Meinert, 1877. B. elegans exhibits unusual variation, of which the taxonomical significance is still unclear. It has been observed for the first time that all species of the genus exhibit an unusual sexual dimorphism on the mandibular palp: in the adult males, the ventral border of the terminal article has a comb of stiff setae which is lacking in females and immature males. Furthermore, a locking system holding together the inner plates of the maxilliped is described and illustrated. A previously overlooked vestigial dactylus on the second and the fifth pereiopod is described.