Hydrochus is the only living genus of beetle in the familyHydrochidae, which belongs to the superfamilyHydrophiloidea, and was formerly treated as a subfamily ofHydrophilidae.Hydrochus includes about 180 species, which are found worldwide.[1] The name "Hydrochus" has also been used for a fly genus in the familyDolichopodidae, but this is a junior subjective synonym of the genusRhaphium.[2]
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.[3] 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 onannelid worms belonging the familyNaididae. The larvae also burrow into crevices, such as hollow dead grass, including to pupate.[4] 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.[1]
Theclub of the seven segmented antennae consists of three segments with a cup-like basal segment. The number oftarsi on the legs are usually 5-5-5 or 4-4-4 (a tiny basal segment can be hard to see). Thepronotum narrows towards the rear but is narrower than the base of theelytra. An African species was formerly described under the genusKiransus, but along with several other African species, it is now placed inHydrochus.[5] Hydrochids are considered to be an older branch of the Hydrophiloidea. Hydrochids have been suggested as a sister group of theSpercheidae and Hydrophilidae, but the relationships are unclear. Molecular phylogenetic comparisons suggest that they are related as a sister group toHelophorus andGeorissus.[6]
^abArchangelsky, M., Beutel, R. and Komarek, A. 2016. Hydrophiloidea Latreille, 1802: Coleoptera, Beetles. In: Schmidt-Rhaesa, A. ed.Handbook of Zoology Online [online]. Berlin, Boston: De Gruyter. [Accessed 2022-10-02]
^Hansen, M. (1998). "The systematic status of Kiransus Makhan, 1994, with the description of three new species of Hydrochus Leach, 1817 (Coleoptera: Hydrochidae)".Insect Systematics & Evolution.29 (2):223–232.doi:10.1163/187631298x00302.
^Short, Andrew Edward Z.; Fikáček, Martin (2013). "Molecular phylogeny, evolution and classification of the Hydrophilidae (Coleoptera): Classification of the Hydrophilidae".Systematic Entomology.38 (4):723–752.doi:10.1111/syen.12024.S2CID83050858.
^Hidalgo-Galiana, A.; Ribera, I. (2011). "Late Miocene diversification of the genus Hydrochus (Coleoptera, Hydrochidae) in the west Mediterranean area".Molecular Phylogenetics and Evolution.59 (2):377–385.doi:10.1016/j.ympev.2011.01.018.PMID21354316.
