Hydrachna bivirgulata Piersig, 1897

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 : 37-38

Hydrachna bivirgulata Piersig, 1897

Species incerta

Holotype lost; no material available. Locus typicus: Leipzig, Großzschocher, forest pools.

For comparison: Hydrachna crassipalpis female, Russia, Yaroslavl, Nekouz, temporary reservoir near Borok, VI 1994 coll. Tuzovskij; male, The Netherlands, Zuid­Holland, polder Vierambacht, 106.34/464.77, 0 3.05.1983 coll. H. Smit; female, The Netherlands, Zuid­Holland, polder Nieuwkoop, 114.27/463.56, 26.04.1983 coll. H. Smit.

Discussion: In the year 1897, Piersig described in two separate papers two species from the same locality, H. bivirgulata Piersig 1897 a (first published as a nomen nudum: Piersig 1895) and H. crassipalpis Piersig 1897 b. On H. bivirgulata he wrote no more than six lines of mostly insignificant information without giving figures. Later on, in the publication of his book (1896–1899), he included a more detailed description and figures of the genital field and frontal area of a female, but not of the taxonomically important palp. Since then, the shape of the frontal plates, not equally curved, but with a kink in the centre, and the presence of tubercles on the inner surface of these rod­shaped sclerites were considered as diagnostic features of H. bivirgulata and the species was recorded from several parts of Europe (see K. O. Viets 1978). However, the species remained little known in most morphological details. Finally, in 1958 Láska gave the first figure of the palp. As pointed out by Lundblad (1969), no differences can be found in the shape of the palp between the description of Láska for H. bivirgulata and H. crassipalpis . The shape of the frontal plates is highly variable in most Hydrachna species, and the internal tuberculation (corresponding to the formation of apodemes for single muscle fibres) increases with age. Lundblad (1969) was correct when he pointed out that concerning an eventual synonymy the name of H. bivirgulata would have priority over H. crassipalpis . However, as we have no information on important morphological details due to the lack of type material, H. bivirgulata should be considered a species incerta. Hydrachna crassipalpis is also not documented by type material; however, the description of the characteristic palp is sufficient for recognizing this species (Davids et al. in press).