Hydrachnidia Krantz, 1978 - water mites
   Superfamily Hydryphantoidea Piersig, 1896 - water mites
     1 Family Ctenothyadidae Lundblad, 1936
     2 Family Hydrodromidae Viets, 1936
     3 Family Hydryphantidae Piersig, 1896
     4 Family Rhynchohydracaridae Lundblad, 1936
     5 Family Teratothyadidae Viets, 1929
     6 Family Thermacaridae Sokolow, 1927 [monotypic]
     7 Family Zelandothyadidae Cook, 1983