Hydrachnidia Krantz, 1978 - water mites
Superfamily Hygrobatoidea Koch, 1842
01 Family Astacocrotonidae Thor, 1927 [monotypic]
02 Family Aturidae Thor, 1900
03 Family Feltriidae Viets, 1926 [monotypic]
04 Family Ferradasiidae Cook, 1980 [monotypic]
05 Family Frontipodopsidae Viets, 1931 [monotypic]
06 Family Omartacaridae Cook, 1963
07 Family Hygrobatidae Koch, 1842
08 Family Lethaxonidae Cook, Smith & Harvey, 2000
09 Family Pionidae Thor, 1900
10 Family Pontarachnidae Koenike, 1910
11 Family Wettinidae Cook, 1956
12 Family Unionicolidae Oudemans, 1909