Hydrachna skorikowi ( Piersig, 1900 )

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 : 50-51

Hydrachna skorikowi ( Piersig, 1900)

Hydrachna schneideri skorikowi Piersig, 1900

Hydrachna skorikowi integra K.Viets, 1930 , syn. nov.

Material examined: Italy: Friuli­Venezia Giulia, Staranzano (GO), foci F. Isonzo, Isola della Cona, Stoch (1/2/1); Hydrachna skorikowi integra K.Viets, 1930 holotype male, SMF 3777; Sicily, numerous specimens from 11 sites, published as " H. skorikowi integra " ( Gerecke 1991) ; Hydrachna schneideri lectotype male, SMNH 373 Heiligenrode, 2370 Ostfriesland (= H. cruenta , see there).

Discussion: The material on which Koenike (1895) based the description of H. schneideri consisted of two specimens. The male (slide number 375) is obviously identical with H. cruenta (Müller, 1776) , but the female (slide number 373) has a distinctly stouter palp and was later named by Koenike (1914) as H. valida . However, this specimen is morphologically identical with a subspecies described in the meantime by Piersig (1900) as H. schneideri skorikowi . As in the description of Koenike no holotype specimen was selected, and also in his hand written catalogue ( NHMB, unpubl.), both specimens are simply designated as " Type ", they are obviously syntypes. When Viets (1935), in a first statement about this problem, based his redescription on the male specimen (slide number 375), in the sense of the rules of the International Code of Zoological Nomenclature, this treatment was equivalent to a lectotype designation. Consequently, the name H. schneideri must be considered a junior synonym of H. cruenta and the valid name for all specimens ever published under this name is H. skorikowi , as was proposed by K. Viets (1935).

This position is in contrast to Lundblad (1956) who pointed out that most of the figures in the original description refer to the female specimen with stout palps. This statement is correct, but in this special situation, the earlier treatment by K. Viets (1935) established a lectotype thus precluding questioning.

The diagnostic feature of a further subspecies described as H. valida integra from Spain ( K. Viets 1930) should be a straight, not medially indented posterior margin of the frontal shield. In fact, numerous specimens from Italy agree with this description, but an examination of populations from other parts of Europe and in Israel reveal a strong individual variability of this character. As is suggested by observations with other frontal shield­bearing species of the genus (e.g. H. inversa Walter, 1927 , see Lundblad 1956), this shield is formed from the fusion of paired plates and this fusion may be more or less complete, in the latter case leaving an unsclerotized posteromedial indentation. Hydrachna skorikowi integra agrees from all other points of view with H. skorikowi and should be considered its junior synonym.