Georgella helvetica Haller, 1882

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 : 8-9

Georgella helvetica Haller, 1882

Hydryphantes helveticus auct.

Georgella apsteini ( Koenike, 1903) , nov. syn.

Material examined: Georgella helvetica , Greece, Lake Himaditis, 3.v.1997, coll. Smit, (1/1/0); Russia, coll. Tuzovskij, prep. 6447 (1/1/0), 6778 (0/1/0). Georgella apsteini , holotype NHUB 33010, Germany " Type 636 Holstein, Colberger Heide, Dr. Apstein coll."

Description: Anterolateral extensions of frontal shield directed laterally, anteromedial margin extending in a triangular projection, frontal eye generally near the base of this projection or in the anterior third of the central plate surface, ratio total L/medial L 1.9-2.2, total L/ W 1.0 -1.2. Medial margin Cx-III+IV straight, posterior margin Cx-IV with two concave sectors, the lateral one more extended, separated by a blunt projection; swimming setae number II-L-4/5 posterior 16-20/23-27; III-L-3/4/5 posterior 6- 8 /15-25/25-34; IV-L-3 anterior 5, posterior 3-8; IV-L-4 anterior 8-20, posterior 27-32; IV-L-5 posterior 25-45; the specimens from Greece differ from those from Russia in bearing only 4-5 swimming setae on II-L-4. Genital flaps indented in the centre or slightly posterior to the centre, on each side with 40-65 acetabula and 30-40 fine setae. One additional pair of acetabula in the membranous integument flanking the gonopore generally present, but occasionally reduced on one or both sides. Gnathosoma stout, with short rostrum, diameter of mouth opening 50-60. Chelicera L/H 3.7-3.9, basal segment/claw 1.6-1.8. Palps stout, with dense setation (seta numbers P- 1-4 2-6, 16 -20, 10-18, 4). P-4 relatively short and stout (L ratio P-2/4 0.76-0.86; L/H P-4 2.38-2.56). Males: Idiosoma L/W 2000-2800/1600-2000, frontal shield total L/medial L/W 540-600/250-380/ 500-570. Genital flap L 390-430; gnathosoma L 320-340, chelicera L 450-470, palp segments L/H P-1, 85-90/ 110, P-2, 150-160/100-120, P-3, 100-120/115-117, P-4, 190-205/80, P-5, 50/25-30. Females: Idiosoma L/W 3000/2400, frontal shield total L/medial L/W 650-720/330-380/600-657. Genital flap L 190-430; gnathosoma L 380-400, chelicera L 520-570, palp segments L/H P-1 95-100/120-130, P-2 175-190/130-155, P-3 120/120- 130, P-4 220-230/90, P-5 50-55/25-30.

Discussion: The holotype of Georgella helvetica is lost, but the species has been frequently recorded from many parts of the W Palaearctic, and Özkan (1981) gave a thorough description of the species based on material from Anatolia. Thus, a wide consensus exists about its general morphology and the species name is well established for populations that fit the following diagnostic characters: (1) Frontal shield nearly as long as wide (L/ W 1.9 -2.2), anterolateral extensions directed laterally and eye located near the anterior margin. (2) Genital field with one pair of acetabula in the gonopore area (rarely reduced as an individual aberration) and 40-65 acetabula on each flap. Haller's (1882) statement concerning the "acetabula-free medial area of genital field" obviously refers to the setate medial part of the genital flaps and cannot be taken as an explicit observation of the absence of this acetabulum - a tiny structure easily overlooked, especially in dark preparations. (3) Palp with relatively short and stout P-4.

A re-examination of the holotype of G. a p s t e i n i shows that the original description is incorrect from many points of view. The specimen was badly damaged during dissection, with left and right coxae separated from each other and partly folded, genital field crushed into many pieces, gnathosoma probably under the lacquer ring, and several leg segments having lost most of their swimming setae. The anterior projection of the frontal shield is long and slender, but basally broader than given in Koenike's (1903) figure, and the frontal eye is definitively not in the centre of this plate, but in the anterior third. Furthermore, coxal setae are not restricted to lateral plate margins, but arranged all over the plates as typical for the genus. As in other species, a line of setae flanks the medial genital flap margin, and several additional setae are scattered over the acetabula-free area of the plate. The shape of rounded remnants of the acetabula-bearing anterior plate margin furthermore indicates that these parts extended anteriorly over the setae-bearing area, flanking a medial indentation at the gonopore anterior margin. The position of the genital field immediately behind the coxal field suggests that the holotype was a rather juvenile specimen, but it was mature (as indicated by the presence of eggs). Observations in other species of the genus testify for the possibility of considerable growth during adult life, with increasing distance between genital field and coxae especially in females.

Under all described points of view, but also in the range of setae numbers and measurements, G. apsteini is in good agreement with G. helvetica . Therefore we consider G. apsteini , a species recorded only once after the first description (from a lake in Russia, Gorschkowa 1924), a junior synonym of G. h e l v e t i c a.