One British genus, Helophorus, with 20 species.  Small (2-7mm) elongate beetles, with the body outline constricted between the elytra and pronotum, they have long palps, similar in size to their antennae and 7 longitudinal grooves on the coarsely-granulate pronotum.  The genus is characteristic of impermanent ponds, often ephemeral pools on grassland, although a few species are associated with dry ground.  Dissection of males is very useful for reliable ID.