Belongs within: Staphylinoidea.
The Hydraenidae are a group of small beetles generally characterised by maxillary palps as long as or longer than their antennae with the antennae usually bearing a five-segmented club. Adults and larvae mostly graze on micro-algae and other organic matter on wet surfaces. The venter of adults is usually covered with hydrofuge pubescence that helps hold a respiratory bubble of air in place when the beetle is submerged (Perkins 2001).
Characters (from Lawrence & Britton 1991): Small with relatively inconspicuous antennae, often concealed within grooves beneath head and cavities between prostemum and pronotal hypomera, and well-developed maxillary palps which may be as long as or longer than antennae; antennae eight- or nine-segmented with five- or six-segmented club, segment preceding club usually forming cupule; fore coxae transverse or globular, trochantins exposed, fore coxal cavities externally and internally open or closed; mid coxal cavities narrowly to moderately separated, laterally open; tarsi pentamerous or tetramerous; abdomen with six or seven ventrites, none connate. Larvae usually elongate, campodeiform, with well-developed legs, articulated urogomphi, and pair of hooks on segment 10.
Hydraenidae [Limnebiidae]
| i. s.: OchtebiitesLC20
| |--O. altusLC20
| `--O. minor Ponomarenko 1985RJ93
| NucleotopsMF15
| ParhydraenaMF15
|--ProsthetopinaeMF15
`--HydraeninaeB14
|--LimnebiiniP01
| |--Laeliaena Sahlberg 1900P01
| `--Limnebius Leach 1915MF15, P01
| |--L. atomusLC20
| |--L. discolorP01
| |--L. furcatusBP00
| |--L. mesatlanticusLC20
| `--L. piceusP01
`--+--HydraeniniP01
| |--+--Orchymontia [Orchymontiinae]LC20
| | `--+--Adelphydraena orchymontiLC20
| | `--Meropathus zealandicus Ordish 1984LC20, E02
| `--Hydraena Kugelann 1794MF15, P01
| | i. s.: H. acutipennis Fairm. 1879M96
| | H. anisonycha Perkins 1980B14
| | H. luridipennisLB91
| | H. reidianaLC20
| | H. ripariaL02
| | H. torrensi Blackb. 1888M96
| | H. (Hydraena)F05
| | |--H. (H.) gavarrensis Jäch, Díaz & Martinoy 2005F05
| | `--H. (H.) marinae Castro 2004F05
| |--H. pulchellaLC20
| `--+--H. californicaLC20
| `--H. castanescensLC20
`--OchthebiinaeB14
| i. s.: TympanogasterLB91
| Hughleechia giulianiiLB91
`--OchthebiiniP01
| i. s.: Neochthebius Orchymont 1932P01
| `--N. vandykeiP01
| Enicocerus Stephens 1829P01
| `--E. benefossusP01
|--+--AulacochthebiusLC20
| `--Gymnochthebius Orchymont 1943LC20, P01
| |--G. laevipennisP01
| |--G. maureenaeP01
| `--G. nitidusP01
`--Ochthebius Leach 1815LC20, P01
| i. s.: O. arenicolusP01
| O. australis Blackb. 1888M96
| O. aztecus Sharp 1887B14
| O. bisinuatusP01
| O. californicusP01
| O. discretusP01
| O. gruwelliP01
| O. lejolisiPP64
| O. lineatusP01
| O. marinus [=Elophorus marinus]G89
| O. nitidulusLC20
| O. puncticollisP01
| O. pygmeusR26
| O. subintegerPP64
|--O. minimusLC20
`--+--O. quadrifoveolatusLC20
`--O. tivelunusLC20
*Type species of generic name indicated
References
[BP00] Bellini, R., F. Pederzani, R. Pilani, R. Veronesi & S. Maini. 2000. Hydroglyphus pusillus (Fabricius) (Coleoptera Dytiscidae): its role as a mosquito larvae predator in rice fields. Boll. Ist. Ent. “G. Grandi” Univ. Bologna 54: 155–163.
[B14] Bouchard, P. (ed.) 2014. The Book of Beetles: A lifesize guide to six hundred of nature’s gems. Ivy Press: Lewes (United Kingdom).
[E02] Emberson, R. M. 2002. The beetle (Coleoptera) fauna of the Chatham Islands: additions and corrections. New Zealand Entomologist 25: 69–77.
[F05] Fernández, J. 2005. Noticia de nuevos táxones para la ciencia en el ámbito Íbero-Balear y Macaronésico. Nuevos táxones animales descritos en la península Ibérica y Macaronesia desde 1994 (IX). Graellsia 61 (2): 261–282.
[G89] Gestro, R. 1889. Viaggio ab Assab nel Mar Rosso dei signori G. Doria ed O. Beccari con il R. Avviso “Esploratore” dal 16 Novembre 1879 al 26 Febbraio 1880.—IV. Coleotteri. Annali del Museo Civico di Storia Naturale di Genova, Serie 2a, 7: 5–72.
[L02] Latreille, P. A. 1802. Histoire Naturelle, générale et particulière des crustacés et des insectes vol. 3. Familles naturelles des genres. F. Dufart: Paris.
[LB91] Lawrence, J. F., & E. B. Britton. 1991. Coleoptera (beetles). In: CSIRO. The Insects of Australia: A textbook for students and research workers 2nd ed. vol. 2 pp. 543–683. Melbourne University Press: Carlton (Victoria).
[LC20] Lü, L., C.-Y. Cai, X. Zhang, A. F. Newton, M. K. Thayer & H.-Z. Zhou. 2020. Linking evolutionary mode to palaeoclimate change reveals rapid radiations of staphylinoid beetles in low-energy conditions. Current Zoology 66 (4): 435–444.
[M96] Masters, G. 1896. Catalogue of the described Coleoptera of Australia. Supplement, part II. Dytiscidae, Gyrinidae, Hydrophyllidae, Staphylinidae, Pselaphidae, Paussidae, Silphidae, Scaphididae, Histeridae, Phalacridae, Nitidulidae, Trogositidae, Colydiidae, Cucujidae, Cryptophagidae, Lathridiidae, Mycetophagidae, Dermestidae, Byrrhidae, Parnidae, Heteroceridae. Proceedings of the Linnean Society of New South Wales 21 (Suppl.): 695–754.
[MF15] McKenna, D. D., B. D. Farrell, M. S. Caterino, C. W. Farnum, D. C. Hawks, D. R. Maddison, A. E. Seago, A. E. Z. Short, A. F. Newton & M. K. Thayer. 2015. Phylogeny and evolution of Staphyliniformia and Scarabaeiformia: forest litter as a stepping stone for diversification of nonphytophagous beetles. Systematic Entomology 40: 35–60.
[PP64] Peres, J. M., & J. Picard. 1964. Nouveau manuel de bionomie benthique de la mer Mediterranee. Recueil des Travaux de la Station Marine d’Endoume, Bulletin 31 (27): 5–137.
[P01] Perkins, P. D. 2001. Hydraenidae Mulsant, 1844. In: Arnett, R. H., Jr & M. C. Thomas (eds) American Beetles vol. 1. Archostemata, Myxophaga, Adephaga, Polyphaga: Staphyliniformia pp. 228–232. CRC Press: Boca Raton.
[R26] Risso, A. 1826. Histoire naturelle des principales productions de l’Europe méridionale et particulièrement de celles des environs de Nice et des Alpes maritimes vol. 5. F.-G. Levrault: Paris.
[RJ93] Ross, A. J., & E. A. Jarzembowski. 1993. Arthropoda (Hexapoda; Insecta). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 363–426. Chapman & Hall: London.