Idotea are relatively large, conspicuous and common marine isopods with oval or oblong bodies. Although they often have striking colours and patterns, these are not particularly useful for distinguishing between the various species. Rather, identification should be based on characteristics of the antennae, the coxal plates and the pleotelson.
Males of I. chelipes grow up to 15 mm in length, whilst females reach 10 mm. The antennules extend well beyond the third segment of the peduncle of the antennae, whilst the coxal plates are narrow, with only those of pereonites 5 to 7 extending to the rear margin. The pleotelson has subparallel sides, obtuse lateral corners, is slightly keeled towards the rear, and has a single rather rounded medial tip. Mostly greenish or brownish in colour.
Distribution and Habitat
I. chelipes is a species of brackish water, being found in algae in estuaries and stream mouths and in brackish pools. It has been recorded on eastern British shores from the Humber southwards, and on southern and western coasts as far north as Shetland, but appears to be absent from the north-east. It has occasionally been recorded on Irish coasts.
Naylor, E. & A. Brandt. 2015. Intertidal Marine Isopods. Synopses of the British Fauna (New Series), No. 3. Field Studies Council, for The Linnean Society of London.