Hydrochus Brevitarsis

''Hydrochus'' is the only living genus of beetle in the family Hydrochidae, which belongs to the superfamily Hydrophiloidea, and was formerly treated as a subfamily of Hydrophilidae. ''Hydrochus'' includes about 180 species, which are found worldwide.Archangelsky, M., Beutel, R. and Komarek, A. 2016. Hydrophiloidea Latreille, 1802: Coleoptera, Beetles. In: Schmidt-Rhaesa, A. ed. ''Handbook of Zoology Online'' nline Berlin, Boston: De Gruyter. ccessed 2022-10-02/ref> The name "''Hydrochus''" has also been used for a fly genus in the family Dolichopodidae, but this is a junior subjective synonym of the genus ''Rhaphium''.

They are found in slow moving streams or stagnant water bodies, where they are associated with dense vegetation. In adults air is stored in a bubble on the underside of the body, with the antennae used to transfer atmospheric air to the bubble. The larvae live at the bottom of water bodies, indicating that they can breathe underwater. The diet is only known for the larvae of one species, ''H. japonicus,'' which feed on annelid worms belonging the family Naididae. The larvae also burrow into crevices, such as hollow dead grass, including to pupate. The adults are sluggish crawlers along surfaces, and are thought to consume algae and plant detritus. Eggs are laid in silk cases, often attached to (usually plant) substrates.

The club of the seven segmented antennae consists of three segments with a cup-like basal segment. The number of tarsi on the legs are usually 5-5-5 or 4-4-4 (a tiny basal segment can be hard to see). The pronotum narrows towards the rear but is narrower than the base of the elytra. An African species was formerly described under the genus ''Kiransus'', but along with several other African species, it is now placed in ''Hydrochus''. Hydrochids are considered to be an older branch of the Hydrophiloidea. Hydrochids have been suggested as a sister group of the Spercheidae and Hydrophilidae, but the relationships are unclear. Molecular phylogenetic comparisons suggest that they are related as a sister group to '' Helophorus'' and '' Georissus''.

The oldest fossil of the modern genus is ''Hydrochus relictus'' from the Green River Formation of North America, dating to the Eocene. An extinct genus of the family, '' Ponohydrochus'', is known from the Early Cretaceous (Hauterivian) Khasurty locality in Russia.

Selected species

More than 180 species have been described in the genus. The following list includes some of the species in the genus:

* '' Hydrochus aljibensis'' Castro & Delgado, 1999 ^g
* '' Hydrochus angusi'' Valladares, 1988 ^g
* '' Hydrochus angustatus'' Germar, 1824 ^g
* '' Hydrochus argutissimus''
* '' Hydrochus aschnaae
* '' Hydrochus basilaris''
* '' Hydrochus bicarinatus''
* '' Hydrochus bituberculatus''
* '' Hydrochus brevis'' ( Herbst, 1793) ^g
* '' Hydrochus brevitarsis'' Knisch, 1922 ^{i c g}
* '' Hydrochus brianbrowni'' Makhan, 2005 ^{i c g}
* '' Hydrochus callosus'' LeConte, 1855 ^{i c g}
* '' Hydrochus collaris''
* '' Hydrochus conjunctus''
* '' Hydrochus corruscans''
* '' Hydrochus crenatus'' (Fabricius, 1792) ^g
* '' Hydrochus currani'' Brown, 1929 ^{i c g b}
* '' Hydrochus debilis'' Sharp, 1882 ^{i c g}
* '' Hydrochus denarius''
* '' Hydrochus drakei'' Knisch, 1921 ^g
* '' Hydrochus elongatus'' (Schaller, 1783) ^g
* '' Hydrochus ensifer''
* '' Hydrochus excavatus'' LeConte, 1855 ^{i c g b}
* '' Hydrochus falsus'' Hellman in Worthington, Hellman, and Lago 2016
* '' Hydrochus farsicus'' ^g
* '' Hydrochus flavipennis'' Küster, 1852 ^g
* '' Hydrochus formosus''
* '' Hydrochus foveatus'' Haldeman, 1852 ^{i c g}
* '' Hydrochus grandicollis'' Kiesenwetter, 1870 ^g
* '' Hydrochus granulatus'' Blatchley, 1910 ^{i c g b}
* '' Hydrochus hellmani''
* '' Hydrochus ibericus'' Valladares, Diaz & Delgado, 1999 ^g
* '' Hydrochus ignicollis'' Motschulsky, 1860 ^g
* '' Hydrochus inaequalis'' LeConte, 1855
* '' Hydrochus jaechi'' Makhan, 1995 ^{i c g}
* '' Hydrochus japonicus'' Sharp, 1873 ^g
* '' Hydrochus jiawanae'' Makhan, 1996 ^{i c g}
* '' Hydrochus kellymilleri''
* '' Hydrochus kirgisicus'' Motschulsky, 1860 ^g
* '' Hydrochus lachmoni''
* '' Hydrochus leei''
* '' Hydrochus lobatus''
* '' Hydrochus mauriciogarciai''
* '' Hydrochus megaphallus'' van Berge Henegouwen, 1988 ^g
* '' Hydrochus minimus'' Blatchley, 1919 ^{i c g}
* '' Hydrochus neosquamifer'' Smetana, 1988 ^{i c g}
* '' Hydrochus nigeriensis''
* '' Hydrochus niloticus''
* '' Hydrochus nitidicollis'' Mulsant, 1844 ^g
* '' Hydrochus nodulifer''
* '' Hydrochus nooreinus'' Berge Henegouwen & Sainz-Cantero, 1992 ^g
* '' Hydrochus obscurus'' Sharp, 1882 ^{i c g}
* '' Hydrochus octocarinatus'' Hochhuth, 1871 ^g
* '' Hydrochus pajnii'' Makhan, 2000 ^{i c g}
* '' Hydrochus pallipes'' Chevrolat, 1863 ^{i c g}
* '' Hydrochus pictus''
* '' Hydrochus pseudosecretus''
* '' Hydrochus pseudosquamifer'' Miller, 1965 ^{i c g b}
* '' Hydrochus pupillus'' Orchymont, 1939 ^g
* '' Hydrochus ramcharani''
* '' Hydrochus roomylae'' Makhan, 2001 ^{i c g}
* '' Hydrochus rishwani''
* '' Hydrochus rufipes'' Melsheimer, 1844 ^{i c g b}
* '' Hydrochus rugosus'' Mulsant, 1844 ^{i c g b}
* '' Hydrochus sagittarius''
* '' Hydrochus scabratus'' Mulsant, 1844 ^{i c g b}
* '' Hydrochus schereri'' Makhan, 1995 ^{i c g}
* '' Hydrochus setosus'' Leech, 1948 ^{i c g}
* '' Hydrochus shorti''
* '' Hydrochus simplex'' Leconte, 1851 ^{i c g b}
* '' Hydrochus soekhnandanae''
* '' Hydrochus smaragdineus'' Fairmaire, 1879 ^g
* '' Hydrochus spangleri'' Hellman in Steiner, Staines, McCann and Hellman, 2003 ^{i c g}
* '' Hydrochus squamifer'' LeConte, 1855 ^{i c g b}
* '' Hydrochus subcupreus'' Randall, 1838 ^{i c g b}
* '' Hydrochus tariqi'' Ribera, Hernando & Aguilera, 1999 ^g
* '' Hydrochus tarsalis'' Chevrolat, 1863 ^{i c g}
* '' Hydrochus vagus'' LeConte, 1852 ^{i c g}
* '' Hydrochus tuberculatus''
* '' Hydrochus variabiloides''
* '' Hydrochus variolatus'' LeConte, 1851 ^{i c g}
* '' Hydrochus yadavi'' Makhan, 2000 ^{i c g}

Data sources: i = ITIS, c = Catalogue of Life, g = GBIF, b = Bugguide.net

References

{{Taxonbar, from=Q10770073, from2=Q1219695

Hydrophiloidea
Staphyliniformia genera