Hydrachnidia Krantz, 1978 - water mites Superfamily Hygrobatoidea Koch, 1842 Family Unionicolidae Oudemans, 1909 1 Subfamily Encentridophorinae Viets, 1935 [monotypic] 2 Subfamily Omanohydracarinae Gerecke, 2004 [monotypic] 3 Subfamily Pionatacinae Viets, 1916 4 Subfamily Pollicipalpinae Viets, 1924 [monotypic] 5 Subfamily Unionicolinae Oudemans, 1909