Formerly part of Dytiscidae, this group has only two representatives in the British Isles.  Both species are found mainly in stagnant water in association with floating rafts of vegetation, often burrowing through mud at the bottom of the pond.  Unusually, members of this family pupate in cocoons attached to the roots of water plants.  The predatory adults can be recognised by the presence of a ‘noterid platform’, a plate between the second and third pairs of legs.