Hydrachnidia Krantz, 1978 - water mites Superfamily Hydryphantoidea Piersig, 1896 - water mites Family Hydryphantidae Piersig, 1896 Subfamily Euthyadinae Viets, 1931 Genus Placothyas Lundblad, 1926 1 Subgenus Placothyas (Placothyas) Lundblad, 1926 2 Subgenus Placothyas (Octothyas) Lundblad, 1945