Hydrachna regulifera Koenike, 1908

Davids, Kees, Sabatino, Antonio Di, Gerecke, Reinhard, Gledhill, Terence & Smit, Harry, 2005, On the taxonomy of water mites (Acari: Hydrachnidia) described from the Palaearctic, part 1: Hydrachnidae, Limnocharidae and Eylaidae, Zootaxa 1061, pp. 36-64 : 50

Hydrachna regulifera Koenike, 1908

Species incerta

Material examined: Holotype deutonymph [not female!] SMNH 552, Germany, Bremen, under the wings of Dytiscus marginalis .

Discussion: Erroneously, Koenike (1908) reported the finding of an adult female of Hydrachna from the subelytral space of a specimen of Dytiscus marginalis . The holotype is badly damaged (genital region mostly missing, P­3­5 lost, frontal sclerites not clearly identifiable, slide dried up), but remnants of acetabula­bearing sclerite strips attached to the medial margins of Cx­3+4 indicate that it is a deutonymph rather than an adult female. Obviously, this specimen had developed in the subelytral space from a protonymph and was ready to leave its host. Large dimensions and the presence of at least 3 setae on Cx­4 indicate that it is related to H. geographica . A definitive placement of this immature specimen remains impossible and it must be regarded a species incerta.