Description of a neotype for Asellus aquaticus Linné, 1758 (Crustacea: Isopoda: Asellidae), with description of a new subterranean Asellus species from Europe

Asellus aquaticus is one of the most common and well-studied freshwater macroinvertebrates in Europe, but its current taxonomic description is inadequate. Therefore, a neotype is designated and described to allow a comparison with a newly described and illustrated species, Asellus kosswigi sp. n. While several troglomorphic Asellus species are known from Japan, this is the first subterranean species of the genus in Europe. It is morphologically, as well as genetically, distinct from all other, local, surface and subterranean populations. Its species status is confirmed by its syntopic occurrence with Asellus aquaticus without any sign of gene flow.