Sperchon (Hispidosperchon) vaginosus Thor, 1902

Sabatino, Antonio Di, Gerecke, Reinhard, Gledhill, Terence & Smit, Harry, 2009, On the taxonomy of water mites (Acari: Hydrachnidia) described from the Palaearctic, part 2: Hydryphantoidea and Lebertioidea, Zootaxa 2266, pp. 1-34 : 24

Sperchon (Hispidosperchon) vaginosus Thor, 1902

Sperchon denticulatus Koenike, 1895 auct., partim

Sperchon (Hispidosperchon) hibernicus Halbert, 1944 : Bader (1957) err. non. S. hibernicus Halbert

Material examined: Switzerland: Bach Luppinen 40km E. Zurich 530m. 17.9.1991 leg. Wieland (1/0/0); Italy, Sicily: I 211A CT Quellen b. S. Domenico (Adrano), 26.10.1985 (1/0/0); I 218 SR F. Anapo/M. Lauro 30.10.1985 (1/0/0); I 250 SR, 22.11.1985 (1/0/0); The Netherlands: Hazelbeek, Prov. Overijssel, 4.10.1995 (1/ 0/0) (T. G. prep. 1408); England: Gussage Bourne, Gussage All Saints, Dorset, SU007100, 12.1974 (1/0/0) (T. G. prep. 1084); stream, Whitbarrow Scar, Cumbria, SD433876, 24.9.1958 (1/0/0) (T. G. prep. 1216); Bere Stream, Bere Heath, Bere Regis, Dorset, 15.8.1977 & 10.10.1977 resp. (2/0/0) (T. G. preps 1232, 1233); River Frome, Cattistock, Dorset, 24.7.1978 (1/0/0) (T. G. prep. 1283); River Frome, Chantmarle, Frome St. Quintin, Frampton, Dorset, ST591022, 15.10.1979 (1/0/0) (T. G. prep. 1308); River Avon (Bristol), Cow Bridge, ST943862, 18.10.1978 (1/0/0) (T. G. prep.1339); River Frome, Cattistock, Dorset, (1/0/0) (T. G. prep. 1347); Scotland: River Dee, Aboyne, Grampian, NO557980, 6.10.1978 (1/0/0) (T. G. prep. 1298).

Discussion: It is apparent from examination of the listings under Sperchon denticulatus in the catalogues of Karl Viets (1956) and Kurt O. Viets (1987) and also in several publications by other authors, that there has been confusion between S. denticulatus Koenike and S. vaginosus Thor. Even the other species in the ‘ denticulatus -group’, S. violaceus Walter , S. hibernicus Halbert and S. monstruosus Bader (syn. to S. hibernicus ) have been severally misidentified. For example, Bader (1957), in describing and illustrating males of his new species S. monstruosus (p.35), actually describes and figures males of S. hibernicus Halbert. Similarly , his description and figures of males of the latter species (p.39) describe and figure males of S. vaginosus Thor. Schwoerbel (1959, p.526) was also aware of Bader's first misidentification when he placed S. monstruosus Bader into synonymy under S. hibernicus Halbert. Thor (1902) described S. vaginosus from a single male from Switzerland, a species subsequently considered by many authors to be conspecific with S. denticulatus . Males of S. denticulatus possess a large (L 156-252, W 210-300) semicircular (anteriorly rounded, posteriorly more-or-less straight) ventral plate between the genital region and the posterior margin of the idiosoma. This plate may or may not include the excretory pore within its posterior boundary. Thor (1902) did not mention such a plate, a plate of such dimensions that he could surely not have missed as his description is quite detailed. None of the material examined has a ‘ denticulatus -like’ ventral plate and all agree well with Thor’s description of S. vaginosus . However, a small round to oval (L 48-66; W 24-36) ventral platelet with its longest axis lying longitudinally, was present in all the specimens examined. Such a platelet could easily have been unobserved by Thor. Ventral plates intermediate in size between those of S. denticulatus and S vaginosus have not been found and to the best of our knowledge, have not been recorded. The palps of both species are stout and have similar setation and both have a P-4 proximal constriction height to P-4 dorsal length ratio of 0.20-0.22. However the ventral pegs of P-4 of S vaginosus are more widely separated than those of S. denticulatus which has the bases of the ventral pegs more-or-less touching. Additionally the shape of the tip of the rod-like anterior ramus of the ejaculatory complex is different in the two species. In S. vaginosus the tip has a U-shaped cleft between the two pairs of angular projections, that of S. denticulatus is shallowly indented with laterally rounded, posteriorly slightly pointed extensions. As a consequence of these apparently stable character differences between the two taxa, Sperchon vaginosus Thor is re-established as a distinct species. Females of both species currently remain enigmatic.