Belongs within: Dolichopodidae.
The Hydrophorinae are a group of dolichopodid flies with pubescent eyes and an often dorsoventrally flattened abdomen (Bickel 2013).
Characters (from Bickel 2013): Male face usually wide; fronto-clypeal suture distinct, at least laterally; clypeus usually produced anteriorly; palps usually large in both sexes, covered with short setae; antennal scape bare; eyes pubescent; pair of large postvertical setae usually present on dorsal postcranium, out of line with postorbital series; posterior mesonotum not strongly flattened; vein M2 absent; crossvein dm–cu equal to or longer than distal section of CuA; abdomen often dorsoventrally flattened; hypopygium encapsulated ventrally near at abdominal apex.
<==Hydrophorinae [Aphrosylinae] B09
|–Paraphrosylus B09
|–Thambemyia B09
|–Liancalus B09
|–Thinophilus Wahlberg 1844 B13
| |–T. eboricoxa Bickel 2013 B13
| |–T. flagellatus B13
| |–T. splendens Grootaert & Meuffels 1984 B13
| `–T. yarraloola Bickel 2013 B13
|–Oedematopus crassitibia B09
|–Diostracus B09
|–Melanderia mandibulata B09, RV81
|–Hypocharassus pruinosus B09
|–Scellus B09
|–Hydatostega viridiflos B09, BW09
|–Hydrophorus Fallén 1823 B13
| |–H. balticus K01
| |–H. intentus RV81
| `–H. praecox (Lehmann 1822) [=Dolichopus praecox] B13
`–Cymatopus B09
|–C. cheesmanae B09
|–C. leopoldi Z94
|–C. tibialis Z94
`–C. wirthi B09
*Type species of generic name indicated
REFERENCES
[B09] Bickel, D. J. 2009. Dolichopodidae (long-legged flies). In: Brown, B. V., A. Borkent, J. M. Cumming, D. M. Wood, N. E. Woodley & M. A. Zumbado (eds) Manual of Central American Diptera vol. 1 pp. 671–694. NRC Research Press: Ottawa.
[B13] Bickel, D. J. 2013. The family Dolichopodidae (Diptera) of the Pilbara region, Western Australia in its Australasian biogeographic context, with the description of 19 new species. Records of the Western Australian Museum Supplement 83: 291–348.
[BW09] Buck, M., N. E. Woodley, A. Borkent, D. M. Wood, T. Pape, J. R. Vockeroth, V. Michelsen & S. A. Marshall. 2009. Key to Diptera families—adults. In: Brown, B. V., A. Borkent, J. M. Cumming, D. M. Wood, N. E. Woodley & M. A. Zumbado (eds) Manual of Central American Diptera vol. 1 pp. 95–156. NRC Research Press: Ottawa.
[K01] Kertész, K. 1901. Legyek [Dipteren]. In: Horváth, G. (ed.) Zichy Jenő Gróf Harmadik Ázsiai Utazása [Dritte Asiatische Forschungsreise des Grafen Eugen Zichy] vol. 2. Zichy Jenő Gróf Harmadik Ázsiai Utazásának Állattani Eredményei [Zoologische Ergebnisse der Dritten Asiatischen Forschungsreise des Grafen Eugen Zichy] pp. 179–201. Victor Hornyánszky: Budapest, and Karl W. Hierseman: Leipzig.
[RV81] Robinson, H., & J. R. Vockeroth. 1981. Dolichopodidae. In: McAlpine, J. F., B. V. Peterson, G. E. Shewell, H. J. Teskey, J. R. Vockeroth & D. S. Wood (eds) Manual of Nearctic Diptera vol. 1 pp. 625–639. Research Branch, Agriculture Canada.
[Z94] Zhang, Z.-Q. 1994. Neothrombiidae (Acari: Trombidioidea) of the world: systematic review with a phylogenetic analysis and descriptions of two new genera. Oriental Insects 28: 205–237.