Hydrachna

Smit, Harry, 2014, Australian water mites of the genus Hydrachna Müller, with the description of five new species (Acari: Hydrachnidia: Hydrachnidae), Zootaxa 3827 (2), pp. 170-186 : 185-186

Key for adults of the Australian Hydrachna species

1. Dorsum with large frontal plate(s) ( Figs. 7 A, 8 A)........................................................... 2

- Dorsum with only very small sclerites ( Fig. 3 a)............................................................. 12

2. Dorsum with a pair of frontal sclerites ( Fig. 7 A)............................................................. 3

- Dorsum with one large frontal plate ( Fig. 8 A)............................................................... 5

3. Dorsal frontal sclerites relatively slender, curved, posteriorly not narrowed ( Fig. 7 A)............... H. longiscutata n. sp.

- Dorsal frontal sclerites relatively wide.................................................................... 4

4. Dorsal frontal plates very wide, pointed posteriorly (see Fig. 5 Smit 1992)......................... H. palustris female

- Dorsal frontal plates less wide, posteriorly narrowed ( Fig. 1 A)...................................... H. conjectoides

5. Dorsum with a simple large frontal plate, without lateral extensions, not surrounding the eyes........................ 6

- Dorsal frontal plate surrounding the eyes or extending laterally or to posterior idiosoma margin....................... 9

6. Posterior margin of frontal plate with a wide indentation (see Table I, fig. 4 Lundblad 1947).......... H. triscutatus female

- Posterior margin of frontal plate straight or only slightly concave................................................ 7

7. Dorsal frontal plate with 2–3 pairs of setae in posterior half (see Fig. 22 Cook 1967)............... H. mysorensis female

- Dorsal frontal plate with one pair of setae in posterior half.................................................... 8

8. Male genital field heart-shaped, longer than wide; fourth coxae of female posteromedially wide ( Figs. 2 C, E)..................................................................................................... H. cordata n. sp.

- Male genital field wider than long, bilobate; fourth coxae of female posteromedially narrow ( Figs. 8 C, E................................................................................................. H. novaehollandica n. sp.

9. Dorsal frontal plate surrounding the eyes, with lateral extensions but not extending to posterior idiosoma margin ( Fig. 1 Smit 1992; fig. 6 Cook 1986).................................................. Male: H. palustris , female: H. bilobata

- Dorsal plates either surrounding the eyes or eyes free, but frontal plate extending to posterior idiosoma margin......... 10

10. Besides the frontal plate also a lateral sclerite present ( Fig. 2 A Lundblad 1947)....................... H. triscutata male

- Only frontal plate present.............................................................................. 11

11. Frontal plate very large, extending onto lateral sides of idiosoma, genital field not bilobate (Fig. 26 Cook 1967)................................................................................................ H. mysorensis male

- Frontal plates only covering dorsum, genital field bilobate ( Figs. 2, 7 Cook 1986)...................... H. bilobata male

12. Small frontal sclerites rod-shaped ( Fig. 3 A)................................................ H. curtiscutata n. sp.

- Small frontal sclerites not rod-shaped.................................................................... 13

13. Palp very stocky, L/H PIII <2.5 ......................................................................... 14

- Palp not very stocky, L/H PIII > 2.6 ...................................................................... 15

14. Fourth coxal plates almost without posteromedial extensions, acetabula small and very numerous ( Fig. 5 A)..... H. hamata

- Fourth coxal with narrow posteromedial extensions, acetabula larger and less numerous ( Fig. 1 Halík 1940). H. approximata

15. Palp very slender, L/H PIII > 4.0............................................................... H. tasmanica

- Palp less slender, L/H PIII <3.9 ....................................................................... 16

16. Males (genital field longer than wide).................................................................... 17

- Females (genital field wider than long).................................................................... 19

17. Male genital field not intended anteriorly ( Fig. 10 B)....................................... H. queenslandica n. sp.

- Male genital field indented anteriorly..................................................................... 18

18. Male genital field deeply indented anteriorly, indentation reaching almost middle of genital field; capitulum elongated ( Fig. 3 D Lundblad 1947)............................................................................ H. australica

- Male genital field less indentated, capitulum not elongated............................................. H. linderi

19. Genital field deeply indented anteriorly, capitulum elongated ( Fig. 3 C Lundblad 1947).............. H. australica female

- Genital field only slightly indented anteriorly, capitulum not elongated ( Fig. 5 D Lundblad 1947)..................... 20

20. PIII more than 280 µm long, genital field more than 400 µm wide.................................. H. linderi female

- PIII less than 200 µm long, genital field less than 300 µm wide........................ H. queenslandica n. sp. female