Hydrodroma

Gerecke, Reinhard, 2017, The water mites of the genus Hydrodroma (Acari, Hydrachnidia, Hydrodromidae) in Europe and Africa, Ecologica Montenegrina 13, pp. 1-24 : 22-23

Key to the European and African Hydrodroma species.

1. Swimming setation strongly reduced (one single, short seta each on II-L-5, III-L-4/5, and IV-L-4/5, Figs 7 F-H).............................................................................................................................................2

- Legs with more numerous swimming setae, at least on IV-L-4/5 located in rows. ............................... 3

2 (1) Palp stout (L/H ratio P-4, 3.7, Fig. 7 E ) ............................................................................... H. rheophila

- Palp slender (L/H ratio P-4,> 3.8, Fig. 4 C )...................................................................... H. perreptans

3 (2) IV-L-5 without swimming setae on the anterior surface........................................................................ 4

- IV-L-5 with swimming setae on both surfaces ...................................................................................... 8

4 (3) Genital field with less than 35 acetabula per plate; body reduced in size (L idiosoma ♂ 550, ♀ 700; Cx-I+II ♂ 150, ♀ 160; genital plate ♂ 120, ♀ 140). .......................................................... H. liberiensis

- Genital field with more than 35 pairs of acetabula per plate; idiosoma and its plates larger. ................ 5

5 (4) II-L-5 with two posterior swimming setae............................................................................................. 6

- II-L-5 with one posterior swimming seta............................................................................................... 7

6 (5) Integument papillae elongate ( Fig. 5 B ); genital field ( Fig. 5 G ) with fewer than 65 acetabula and 30 pairs of medial setae per plate............................................................................................... H. capensis

- Integument papillae more flattened; genital field with 65-120 acetabula and 45-140 medial setae per plate. ....................................................................................................................................... H. zhokovi

7 (5) Number of swimming setae: III-L-4 posterior 2-5, IV-L-4 anterior 2-6. ............................. H. reinhardi

- Number of swimming setae: III-L-4 posterior> 9, IV-L-4 anterior> 9. ........................... H. despiciens

8 (3) Number of swimming setae: II-L-5 posterior> 4, IV-L-5 posterior> 10; leg claws relatively small (L ratio claw/segment 5, 7-12 %); integument papillae of one type, distinctly separate, slender and sharply pointed ( Fig. 6 D-E). ................................................................................................... H. pilosa

- Number of swimming setae: II-L-5 posterior 1, IV-L-5 posterior <10; leg claws relatively large (L ratio claw/segment 5, 11-18 %); integument papillae heterogenous (for H. trigonometrica not well described), not pointed ( Figs 3 C-B, 5 F). ............................................................................................. 9

9 (8) Genital field with less than 30 acetabula per plate, genital plates short (L <200) ( Fig. 5 G ); body size small (idiosoma L <1000).......................................................................................... H. trigonometrica

- Genital field with more than 45 acetabula per plate, genital plates longer (L> 220), body larger in size (idiosoma L> 1200). ....................................................................................................... H. torrenticola

Figures

Figure 3. Hydrodroma torrenticola, Germany, Heiligenrode. A-C. male, integument papillae; A, C, in top view, B in tangential view; D. male, anterior coxal plate.

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.

Figure 5. A-E. Hydrodroma capensis, male, SMF 43882. A. anterior coxal plate; B. integument papillae in tangential view; C. integument papillae in top view (magnification as in B.); D. ejaculatory complex, anterior view; E. chelicera; F-G; H. trigonometrica; F. Male from Algeria, integument tangential; G. female holotype, genital field.

Figure 6. Hydrodroma pilosa, Germany, Mindelsee. A. male, anterior coxal plate; B. male genital field; C. male, ejaculatory complex lateral; D. Integument in tangential view; E. integument in top view.

Figure 7. A-B. Hydrodroma liberiensis, integument papillae in tangential and top view. A. holotype male; B. paratype female. C.-H. H. rheophila, female from Lesbos (photographs and drawings: Vladimir Pešić). C. integument in tangential view; D. integument in top view (magnification as in C.); E. palp; F. II-L-4-5; G. III-L-4-6; H. IV-L-4-6.