Hydraenidae
Hydraenidae is a family of very small aquatic beetles, sometimes called "Minute moss beetles", with a worldwide distribution. They are around 0.8 to 3.3 mm in length. The adults store air on the underside of the body as well as beneath the elytra which allows them to crawl underwater, often on the underside of the water surface tension, though they cannot swim. Some species have gills that effectively allow them to stay underwater indefinitely. Larvae vary from being fully terrestrial, to being aquatic at least in their earliest instars. The diet of hydraenid larvae and adults is thought to consist of algae, spores and other plant matter. At least some hydraenid adults use stridulation to communicate. There are around 1,300 species in 42 genera.
Genera
These 56 genera belong to the family Hydraenidae:Adelphydraena Perkins, 1989Archaeodraena Jäch & Yamamoto, 2017Aulacochthebius Kuwert, 1887Calobius Wollaston, 1854Cobalius Rey, 1886Coelometopon Janssens, 1972Davidraena Jäch, 1994Decarthrocerus Orchymont, 1948Discozantaena Perkins & Balfour-Browne, 1994Edaphobates Jäch & Díaz, 2003-01Enicocerus Stephens, 1829Ginkgoscia Jäch & Díaz, 2004-01Gondraena Jäch, 1994Gymnanthelius Perkins, 1997Gymnochthebius Orchymont, 1943Haptaenida Perkins, 1997Heptaenida Perkins, 1997Homalaena Ordish, 1984Hughleechia Perkins, 1981Hydraena Kugelann, 1794Hydraenida Germain, 1901Hydroenida Germain, 1901Hymenodes Mulsant, 1844Laeliaena Sahlberg, 1900Limnebius Leach, 1815Madagaster Perkins, 1997Menomadraena Perkins, 2017Meropathus Enderlein, 1901Micragasma Sahlberg, 1900Neochthebius Orchymont, 1932Nucleotops Perkins & Balfour-Browne, 1994Ochtebiites Ponomarenko, 1977Ochthebius Leach, 1815Ochtheosus Perkins, 1997Oomtelecopon Perkins, 2005Orchymontia Broun, 1919Parasthetops Perkins & Balfour-Browne, 1994-31Parhydraena Orchymont, 1937Parhydraenopsis Perkins, 2009-16Phothydraena Kuwert, 1888Pneuminion Perkins, 1997Podaena Ordish, 1984Prionochthebius Kuwert, 1887Prosthetops Waterhouse, 1879Protochthebius Perkins, 1997Protosthetops Perkins, 1994Protozantaena Perkins, 1997Pterosthetops Perkins, 1994Sebasthetops Jäch, 1998-01Sicilicula Balfour-Browne, 1958Spanglerina Perkins, 1980Trinomadraena Perkins, 2017Tympallopatrum Perkins, 1997Mesoceration Janssens, 1967Parhydraenida Balfour-Browne, 1975Tympanogaster Janssens, 1967Extinct genera
- †Archaeodraena Jäch and Yamamoto 2017, Burmese amber, Myanmar, Late Cretaceous
- †Ochtebiites Ponomarenko 1977 Abasheva Formation, Russia, Early Jurassic, Ichetuy Formation, Russia, Karabastau Formation, Kazakhstan, Late Jurassic, Mogotuin Formation, Mongolia, Early Cretaceous