Hydrachna
Hydrachna is a genus of mites in the family Hydrachnidae, the sole genus of the family. There are more than 80 described species in Hydrachna. Larvae of this genus are known to be parasites of water beetles such as Eretes griseus by attaching to the back of the thorax and abdomen. These water mite larvae are also hosts of Callicorixa, Corixa, Cymatia and Sigara species, although Sigara falleni has been described as "immune" to these mites, and Cymatia coleoptrata and Sigara striata also gain this "immunity" after a few years of interaction.
Species
These 87 species belong to the genus Hydrachna:Hydrachna analis Viets & K.Hydrachna approximata Halik, 1940Hydrachna baculoscutata Crowell, 1960Hydrachna batorligetiensis Szalay, 1953Hydrachna bilobata Halik, 1940Hydrachna bimaculata KoenikeHydrachna bisignifera Viets & K.Hydrachna brehmi Szalay, 1955Hydrachna bulgarensis K.Viets, 1940Hydrachna canadensis Marshall, 1929Hydrachna comosa Koenike, 1896Hydrachna conjecta Koenike, 1895Hydrachna conjectoides Lundblad, 1947Hydrachna cordataHydrachna crenulata Marshall, 1930Hydrachna cronebergi Koenike, 1897Hydrachna cruenta Muller, 1776Hydrachna curtiscutataHydrachna danubialis Laska, 1964Hydrachna denudata Piersig, 1896Hydrachna distincta Koenike, 1897Hydrachna dorsoscutata Viets & K.Hydrachna eugeni K.H.Viets, 1911Hydrachna extorris Koenike, 1897Hydrachna geographica Muller, 1776Hydrachna georgei Soar, 1908Hydrachna globosa Hydrachna goldfeldi Thor, 1916Hydrachna guanajuatensis CookHydrachna halberti Soar, 1908Hydrachna hamata Lundblad, 1947Hydrachna hesperia Lundblad, 1934Hydrachna heterophthalma Viets & K.Hydrachna hormuzakii Husiatinschi, 1937Hydrachna hungerfordi Lundblad, 1934Hydrachna hutchinsoni Lundblad, 1934Hydrachna incognita Hydrachna inermis Piersig, 1895Hydrachna inversa Walter, 1927Hydrachna juncta Walter, 1926Hydrachna laceriscuta Lundblad, 1941Hydrachna leegei KoenikeHydrachna levigata Koenike, 1897Hydrachna levis Williamson, 1913Hydrachna linderi Lundblad, 1947Hydrachna longiscutataHydrachna lupus Wainstein, 1976Hydrachna magniscutata Marshall, 1927Hydrachna marita Wainstein, 1966Hydrachna marshallae Lundblad, 1934Hydrachna microscutata Marshall, 1929Hydrachna miliaria Berlese, 1888Hydrachna miyazakii Uchida, 1937Hydrachna multipora Cook, 1967Hydrachna mysorensis Cook, 1967Hydrachna mystomirabilis Habeed, 1954Hydrachna neocaledonica Smit, 2002Hydrachna nonlamellata Viets & K.Hydrachna novaehollandicaHydrachna oculoscutata Smit, 2002Hydrachna orientalis Thon, 1905Hydrachna paludosaHydrachna palustris Smit, 1992Hydrachna papilligera K.H.Viets, 1919Hydrachna perpera Koenike, 1908Hydrachna piersigi Koenike, 1897Hydrachna processifera Koenike, 1903Hydrachna queenslandicaHydrachna rectirostris Viets & K.Hydrachna rhopaloidea K.H.Viets, 1942Hydrachna rotunda Marshall, 1930Hydrachna rubicunda K.H.Viets, 1930Hydrachna schneideri Koenike, 1895Hydrachna similans Marshall, 1928Hydrachna simulans Marshall, 1928Hydrachna sistanica Pesic, Smit & Saboori, 2012Hydrachna stipata Lundblad, 1934Hydrachna tasmanica Lundblad, 1947Hydrachna tchadensis Smit, 1994Hydrachna tenuissima Viets, 1935Hydrachna testudinata CookHydrachna trilobata Viets & K.Hydrachna triscutata Lundblad, 1947Hydrachna validaHydrachna ventrifissa Viets & K.Hydrachna vulpes Wainstein, 1976Hydrachna williamsoni Soar, 1908