The species complex of Diamysis Czerniavsky, 1882, in fresh waters of the Adriatic basin (NE Mediterranean), with descriptions of D. lacustris Bǎcescu, 1940, new rank, and D. fluviatilis sp. nov. (Mysida, Mysidae)

Most populations of Diamysis Czerniavsky, 1882, living in freshwater tributaries of the Adriatic Sea, belong to D. fluviatilis sp. nov., which is distinguished from its congeners mainly by the peculiar distribution of fringes on the carapace of males. A small number of freshwater bodies is inhabited by the more euryhalobious D. mesohalobia heterandra Ariani & Wittmann, 2000. A first description is given for adults of both sexes of D. bahirensis mod. lacustris B¢acescu, 1940, formerly known only from one subadult female taken in the near-coastal freshwater lake Scutari (SE Adriatic). This taxon is raised to species level as D. lacustris, based on the shallow telson cleft and the undulate margins of the scutellum paracaudale in both sexes, and on peculiar features of the male. All freshwater records of Diamysis species so far confirmed for the Mediterranean are restricted to tributaries of the Adriatic basin. This is possibly related to transgressive-regressive events during the Pliocene-Pleistocene, causing alternations between marine and freshwater-terrestrial phases in this semi-enclosed basin, particularly in the area where the sedimentary basin of the Po river evolved.