Corophium arenarium was first described by CRAWFORD in his excellent review of the entire genus, in 1937. In the description, the author expressed his doubt already whether it might be a distinct species or merely a variety of C. volutator. CRAWFORD’S observations on the variation of the number of spines on antenna II, segment 4 and 5, suggest that it is only a variety. CHEVAIS, 1937, does not give a definite opinion, whether he considers the species distinct from each other or not. For biometrical reasons, as well for reasons of variation observed by other authors, he suggests, however, that C. volutator and C. arenarium are only local races of one species.