Hydrodroma ocellata ( Walter & Bader, 1952 )

Gerecke, Reinhard, 2017, The water mites of the genus Hydrodroma (Acari, Hydrachnidia, Hydrodromidae) in Europe and Africa, Ecologica Montenegrina 13, pp. 1-24 : 18

Hydrodroma ocellata ( Walter & Bader, 1952)

( Figs 4 B, F )

Species incerta

Type series: NHMB, holotype ♂ on two slides: " Diplodontus ocellatus Walter Koptawelil 20.12.32 Coll. Chappuis 2" "1352 TYPUS XXII/42" [idiosoma]; Diplodontus ocellatus Walter Mundgliedm. Koptawelil 20.12.32 Coll. Chappuis 2" "1353 TYPUS XXII/43". Both slides in bad state of conservation (dried, squeezed) .

Discussion: Considering the extremely reduced leg swimming setation (in total only 4 short setae, located anterior on III-L-4/5 resp. posterior on IV-L-4/5), this species is obviously close to H. perreptans , not taken in consideration in the discussion of the original description. Also the integument papillosity ( Fig. 4 F ), as well as most measurements and the numbers of idiosoma setae and acetabula, are close to the few data available for that species. In general, the holotype of H. ocellata is a little larger in dimensions (e.g., L/W Cx- I+II, 278/193, C-III+IV, 270/245, genital plate L 225 µm). Stouter proportions of leg and palp segments are possibly due to squeezing, a proportionally large size of leg claws (ratio claw L/segment 5 L about 20 %) is found as in H. perreptans .

The name-giving condition of the lateral eyes (anterior lens bay far larger than posterior one) is difficult to observe in the holotype preparation ( Fig. 4 B ). Also in some of the investigated specimens of H. perreptans , both lenses differ remarkably in size ( Fig. 4 A ), but this character state is not easy observed in slide mounted material: In general, the anterior lens has the shape of a football, the posterior one of a baseball, with the result that measurements may vary due to its inclination. A judgement about the shape of the integument papillae is impossible due to the bad state of conservation of the holotype.

With our present knowledge, a decision on the taxonomic state of H. ocellata is impossible. The closely related H. perreptans appears distributed over many parts of Africa, much more material is necessary in order to understand its intraspecific variability (e.g. concerning the shape of lateral eye lenses) and/or the existence of cryptic sister species.

Figures

Figure 4. A. Hydrodroma perreptans, Liberia, female, lateral eye; B. H. ocellata, holotype male lateral eye; C-E. Hydrodroma perreptans, Liberia, female; C. Combined after original description and various slides, palp; D. integument in top view; E. integument in tangential view; F. H. ocellata, holotype male, integument in top view.