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. linearis grow up to 40 mm in length, whilst females are smaller. The species has an elongated, oblong shape with an emarginate tip to the pleotelson (younger individuals may have a medial tooth). The antennae are long and the antennule extends beyond the second segment of its peduncle. The coxal plates are small and do not extend from the front to the back of any of the pereonites. Green or brown body colouring sometimes with pale marks.
Distribution and Habitat
Recorded all around the shores of Britain and occasionally of Ireland, but it is mainly a sublittoral species and is commonest in the south and west. It may be encountered swimming in shallow water at low tide on sandy shores, and is often associated with Zostera (Eelgrass).
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.