Water diviners described: six new species of the Niphargus aquilex complex (Crustacea, Amphipoda)

With the onset of molecular taxonomy, it has been recognized that groundwater crustaceans in the family Niphargidae Bousfield, 1977 (Crustacea, Amphipoda) can demonstrate either highly variable or static phenotypes. Thus, it is recommended that new species descriptions follow an integrative taxonomic approach, considering morphotaxonomic and molecular characteristics to establish new taxa. The morphospecies Niphargus aquilex Schiødte, 1855 has its main distribution area in Central Europe, spanning southern England, the northern half of France, the Benelux countries, Germany and the Czech Republic. Genetic analyses have shown that it comprises a highly diverse species complex, including amongst others the well-recognized morphospecies Niphargus schellenbergi S. Karaman, 1932. In this study, we describe six new species based on available adult males and females – Niphargus luxemburgensis Weber, Weigand & Brad sp. nov., N. palatinensis Weber & Brad sp. nov., N. normandiensis Weber & Brad sp. nov., N. wasgauensis Weber & Brad sp. nov., N. saraviensis Weber & Brad sp. nov., N. lotharingiensis Weber & Brad sp. nov. – taking a re-evaluated published genetic backbone as a further reference into account. The six newly described species appeared pseudocryptic, as minor morphological differences were noticed. A short discussion of the morphological and molecular delimitations is provided.