Australian water mites of the genus Hydrachna Müller, with the description of five new species (Acari: Hydrachnidia: Hydrachnidae) Author Smit, Harry text Zootaxa 2014 3827 2 170 186 journal article 45299 10.11646/zootaxa.3827.2.3 afea86b1-c1b9-4707-8972-61fcb1246bf3 1175-5326 225232 F7FB55C7-DAA7-47DA-A04D-27B98D6D09AF Key for adults of the Australian Hydrachna species 1. Dorsum with large frontal plate(s) ( Figs. 7A , 8A )........................................................... 2 - Dorsum with only very small sclerites ( Fig. 3a )............................................................. 12 2. Dorsum with a pair of frontal sclerites ( Fig. 7A )............................................................. 3 - Dorsum with one large frontal plate ( Fig. 8A )............................................................... 5 3. Dorsal frontal sclerites relatively slender, curved, posteriorly not narrowed ( Fig. 7A )............... 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. 1A )...................................... 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. 2C, E )..................................................................................................... H. cordata n. sp. - Male genital field wider than long, bilobate; fourth coxae of female posteromedially narrow ( Figs. 8C, 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. 2A 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. 3A )................................................ 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. 5A )..... 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. 10B )....................................... 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. 3D Lundblad 1947 )............................................................................ H. australica - Male genital field less indentated, capitulum not elongated............................................. H. linderi 19. Genital field deeply indented anteriorly, capitulum elongated ( Fig. 3C 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