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. metallica grow up to 30 mm in length, whilst females reach 18 mm. The species is an oblong shape, with a squarish pleotelson. There is a transverse furrow on the head, the antennae are short, and the antennules just extend beyond their third segment. The coxal plates are distinctive, being triangular in shape and extending from the front to the back of pereonites 2 or 3 to 7. The body colour is grey or brownish.
Distribution and Habitat
This north-west Atlantic species is occasionally recorded on western British and Irish shores in material carried across the ocean, such as Goose Barnacles, driftwood and bait boxes.
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.