[1] Formerly a much larger genus, many species have been transferred to segregate genera such as Monocorophium and Crassicorophium.

Corophium contains 12 species,[2] after the genus was divided into a number of new genera in 1997:[3] C. arenarium may reach 7 mm long and looks very similar to C. volutator.

[4] C. multisetosum may grow to 9 mm and builds mud burrows in clay or sand in fresh or weakly brackish habitats.

[5] C. volutator inhabits the upper layers of sand on the coasts of the Netherlands, Germany, the United Kingdom and France, as well as in the Bay of Fundy, New Brunswick, Canada.

They grow to 10 mm, and can occur in huge quantities: up to 40,000 per square metre have been observed.