Identification of a cryptic lineage within Potamon fluviatile (Herbst) (Crustacea : Brachyura : Potamidae)

Based on mitochondrial and nuclear DNA-sequence data we identify and describe an evolutionary separate lineage (Potamon pelops, sp. nov.) within the potamid freshwater crab species Potamon fluviatile (Herbst, 1785). So far, Potamon pelops, sp. nov. is only reported from the Peloponnesus Peninsula (Greece), probably allopatric to P. fluviatile. This cryptic lineage is not identical with the infrasubspecies Potamon fluviatile fluviatile natio laconis Pretzmann, 1983, the latter being within the morphological variation of Potamon fluviatile and Potamon pelops. Morphologically, Potamon pelops, sp. nov. differs from Potamon fluviatile, probably in spermatophore packing (cleistospermia in P. fluviatile versus coeno- and cleistospermia in P. pelops).