Hydrobaenus Fries; Saether 1976: 54; Cranston et al. 1983: 175, 1989: 204; Coffman et al. 1986: 181; Sasa & Kikuchi 1995: 164; Makarchenko & Makarchenko 2006 b: 319, 501, 646; Ashe & O'Connor 2012: 311; Andersen et al. 2013: 226.
Type species: Hydrobaenus lugubris Fries, 1830, by original designation. Senior homonym of Hydrobaenus Fries, 1831.
Generic diagnosis (emended). Based on a new Far-Eastern material and references by Cranston et al. (2007); Makarchenko et al. (2009); Makarchenko & Makarchenko (2010, 2011, 2012); Zerguine & Rossaro (2010), the generic diagnosis given by Saether (1976), Cranston et al. (1983, 1989), Coffman et al. (1986) and Andersen et al. (2013) should be emended as follows:
Adult male. Acrostichals absent or present, when present, then weak and short, not strong decumbent, beginning close to antepronotum or some distance from antepronotum, or situated only in middle part of scutum. Pseudospurs present on tarsomere 1 and often tarsomere 2 of mid and hind legs, occasionally absent. Virga consisting of a cluster of few spines or absent. Oral projections of transverse sternapodeme pointed, rod-shaped or roundish triangular. Gonostylus with one or rarely several megasetae.
Pupa. Tergite II with posterior hooklets or with posterior group of simple spinules with apex pointed orally. Pedes spurii A present on sternites IV–VI or IV–VIII, occasionally absent. Segment I with 1–3 L setae from one side; segment II with 3–4 L setae; segments III–VI each with 4 L setae 0–1 of them taeniate on IV, 0–2 taeniate on V, 0–4 taeniate on VI; segment VII with 3 or usually, 4 L setae, 0–4 of them taeniate; segment VIII usually with 4– 5 taeniate L setae, sometimes with 4 strong simple L setae. Anal lobe usually with 3, occasionally with 6–7 anal macrosetae and with full to reduced fringe of short setae or sometimes without fringe. Male genital sac ending near or extending beyond of anal lobe, with or without of short apical projection or protuberance.
Larva. Antenna with 5–6 segments; if antenna with 6 segments, the sixth segment vestigial. S I plumose or sometimes palmate. Mentum with 1–2 median and 6 pairs of lateral teeth or sometimes with 2 median and 5 pairs of lateral teeth.