Re-established after hundred years: Definition of Hygrobates prosiliens Koenike, 1915, based on molecular and morphological evidence, and redescription of H. longipalpis (Hermann, 1804) (Acariformes, Hydrachnidia, Hygrobatidae)

DNA-barcodes reveal that European populations attributed to Hygrobates longipalpis (Hermann, 1804), thus far considered a common inhabitant of standing and slowly flowing running waters all over the Western Palaearctic, represent two distinct lineages, both widely distributed over the continent. They are differentiated also from an ecological point of view, with specimens from standing waters ("clade I") separated from specimens collected in slowly running waters ("clade II"). Morphological examination revealed that, based on the length ratio of proximo- and distomedial setae on terminal segments of fourth legs, two morphospecies correspond to these two clades. As molecular examination of a specimen from the type locality of H. prosiliens Koenike, 1915 (Bremen, Heiligenrode) shows that it belongs to "clade I", populations from standing waters are attributed to that species. In view of the sketchy original description, loss of holotype and insufficient locality data of H. longipalpis, we arbitrarily assign to it stream-dwelling populations of "clade II" and designate a neotype.

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