Hydrachnidia Krantz, 1978 - water mites Superfamily Arrenuroidea Thor, 1900 Family Mideopsidae Koenike, 1910 1 Subfamily Mideopsinae Koenike, 1910 2 Subfamily Gretacarinae Viets, 1978 [monotypic] 3 Subfamily Guineaxonopsinae Imamura, 1983 4 Subfamily Plaumanniinae Lundblad, 1936 [monotypic]