; subclass Pterygota, order Coleoptera)
Family of beetles, 1–40 mm long, most of which have a Y-shaped impressed line on the vertex. The maxillary palps are usually longer than the antennae, which, in aquatic forms, have a respiratory function. The aquatic species are dark, convex, and shiny. Females carry eggs beneath the abdomen in a silk cocoon. Adults are usually phytophagous; larvae are carnivorous. Land-living species are associated with damp places and dung, and are often paler than aquatics, with more heavily sculptured elytra. There are 2000 species, and their distribution is more abundant in the tropics.