G.O. Sars, 1897
Body oblong oval. Antenna 1 more or less reaching the distal end of article 3 of the peduncle of antenna 2; antenna 2 flagellum longer than peduncle, 1/4 to 1/5 of the body length. Cephalon subquadrate, eyes dorsolateral, prominent. Maxillipedal palp of four articles. Coxal plates wide, extending the whole length of each segment from pereional segment 2 or 3 to 7. Pereiopods all more or less alike. Pleon of two complete segments, and one partial suture in the pleotelson. Pleotelson with the sides fairly straight and converging posteriorly; posterior border characterised by a median obtuse tooth, and obtusely rounded lateral shoulders; keeled. Uropods uniramous.
Males recognizable from about 8 mm, ranging to nearly 30 mm; adult females range from 10 to 16 mm. Colour often uniformly brownish, sometimes with white longitudinal lateral markings, and occasionally with white marbling over the whole dorsal surface; adult females mostly darker than males.
Generally sublittoral on accumulations of detached algae or fish waste, but also between tidemarks, usually in company with Idotea baltica and Idotea emarginata among cast up drift weed.
On fully marine European coasts from Norway to France.