Water penny beetles. Adults are terrestrial and found on riparian vegetation and rocks; occasionally are found underwater where the females lay their eggs. Adults are soft-bodied, oval to ovate; body size ranges from 3-7 mm; coloration black or brown, but some taxa have red or yellow spots; antennae 11-segmented; antennae may be moniliform (bead-like) or serrate or flabellate (segments much wider than long).

Larvae found in riffles or at stream margins; body flattened, disk-like, hence the name water penny; legs 4-segmented, but not visible from above; abdomen may have an operculum and retractile gills (Acneus) or no operculum, with 4-5 pairs of multi-branched tracheal gills (Eubrianax and Psephenus).