Hydrachna incognita ( Wainstein, 1976 )

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 : 46-47

Hydrachna incognita ( Wainstein, 1976)

Material examined: Hydrachna incognita two males, three females, 30.04.1993 Belarus, Maèulišèy, on the south of Minsk, intermittent water body, leg. M. Moroz, det. M.Cichocka; one female, Russia, Samara, Stavropol, National Park Samara Luka, sedgy bog near village Koltsovo, 30.05.1999 coll. Tuzovskij. For comparison: Hydrachna leegei one male, one female, Sweden, SMNH 5330, 5332.

Discussion: This species was mostly defined from the morphology of larvae. Only a few female idiosoma measurements are published and the male has not yet been described. Following the original description, important characters regard the sclerite dots in the frontal area (separate, not fused to longish platelets); genital field L 350, deeply indented anteriorly, maximum W 470, acetabula extend posteriorly to the level of the tip of the indentation, in the posterior part groups of hairs; gnathosomal rostrum L 430; palp similar to H. leegei , L measurements: P­1 165, P­2 205, P­3 245, P­4 (obviously not considering the dorsodistal extension) 75, P­5 50. Our study of a male and a female from Belarus give the following additional information. Male: Sclerites near postocularia L 160, coxal field L 700, Cx­4 bearing one seta; genital field L/W 420/480, gnathosomal base L 300, rostrum L 310; chelicera L 960; palp total L 600, setae: P­1 two dorsodistal, P­3 five to seven dorsal and two to three lateral, P­3 two dorsal and three to four lateral; measurements (L/ H) P­1 150/180 (0.8), P­2 145/95 (1.5), P­3 185/70 (2.6), P­4 85/40 (2.1), P­ 5 35/20 (1.8). Female: Sclerites near postocularia L 110–180, coxal field L 640–950, Cx­4 bearing one seta; genital field L/W 310–380/430–515, gnathosoma base L 380–450, rostrum L 410–470; chelicera L 1150–1360; palp total L 760–860, setation as in male; measurements (L/H) P­1 170–200/200–250 (0.8–0.9), P­2 200–220/120–145 (1.5–1.7), P­3 230–280/ 80–95 (2.9–3.0), P­4 110–115/50–53 (2.2), P­5 45–50/25–27 (1.7–2.0).

Discussion: Hydrachna incognita , H. leegei and a further species described from Russia, H. vulpes Wainstein, 1976 , form a group of taxa at the adult stage grading into each other with regard to shape and arrangement of the frontal sclerites. Currently, it is difficult to find clear points of separation between these taxa. Obviously, the extent of sclerotization of the muscle attachments in the frontal area is rather variable and may be different at the right and left side of the same specimen. The results of our measurements furthermore demonstrate a large variability range of female H. incognita and agreement with H. leegei from most points of view. However, in both sexes of H. incognita a difference is found in the stouter P­3 (L/H ratio <3.0, in H. leegei > 3.3).