Hydrachnidia Krantz, 1978 - water mites 1 Superfamily Hydrovolzioidea Thor, 1905 2 Superfamily Eylaoidea Leach, 1815 3 Superfamily Hydrachnoidea Leach, 1815 [monotypic] 4 Superfamily Hydryphantoidea Piersig, 1896 - water mites 5 Superfamily Lebertioidea Thor, 1900 6 Superfamily Hygrobatoidea Koch, 1842 7 Superfamily Arrenuroidea Thor, 1900