New insights into the origin and phylogeny of Niphargidae (Crustacea: Amphipoda), with description of a new species and synonymization of the genus Niphargellus with Niphargus

The intriguing origin and distribution of subterranean amphipods of the family Niphargidae, particularly in north-western Europe and the British Isles, were heavily influenced by Pleistocene glaciations, which obscured most ancient events. The discovery of a new species in Brittany (described herein as Niphargus quimperensis sp. nov.) that is closely related to two tiny endemic species of the British Isles (one ascribed to the genus Niphargus and the other to Niphargellus), along with further collection of specimens of Niphargellus in Europe, allowed the construction of a comprehensive molecular phylogeny and a new time-calibrated tree of the family Niphargidae. The discovery of Niphargus quimperensis sp. nov. confirmed the position of its clade as sister to all other niphargids. Moreover, phylogenetic analysis demonstrate that the genus Niphargellus is polyphyletic and must be treated as a junior synonym of Niphargus. Finally, we propose that the colonization of continental freshwater by the marine ancestors of Niphargus may have occurred in north-western Europe during the opening of the North Atlantic in the Late Cretaceous, whereas the split of Niphargus quimperensis sp. nov. from the other representatives of its clade may have been related to the isolation of Brittany from the British Isles in the Early Miocene.