Body very robust; pereion and pleosome segments distinctly carinate; development of carinae variable, increasing in size posteriorly; urosome segment 1 with a rounded dorsal carina. Coxal plates moderately large, increasing in size from 1 to 4, plate 1 with anterior angle subacute. Epimeral plate 3 posterior margin convex, distal angle subacute. Head with lateral lobes broadly truncated, eyes large but occupying less than half lateral surface of head and widely separated dorsally, eyes rounded in small specimens becoming oval-kidney-shaped in large specimens. Antennae robust; antenna 1 about one-third body length, flagellum multiarticulate, with tufts of short setae, calceolate in male; accessory flagellum about 5 to 7-articulate. Antenna 2 peduncle article 5 slightly shorter than 4, flagellum multiarticulate; calceolate in male and female. Gnathopod 1 slightly smaller than 2, carpus with broad setose posterior lobe, propodus narrowly oval, palm strongly oblique, palmar margin setose and with 3 or 4 major spines. Gnathopod 2 generally similar to 1. Pereiopods 3 and 4 slender; pereiopods 5 to 7 robust; pereiopod 7 spinose, basis with posterior margin weakly crenate and irregularly rounded. Uropods 1 and 2 spinose, outer ramus little shorter than inner; uropod 3 outer ramus slightly longer than inner, rami lanceolate with inner margins setose. Telson longer than broad, apex weakly emarginate, with few small apical and lateral spinules; telson more elongate in larger specimens.
Up to 35 mm, female larger than male.
Variable olive-green or yellowish, mottled with brown.
Subtidal, occasionally intertidally at extreme low water.
North Atlantic and Arctic Ocean, widespread; American and European coasts; Baltic and North Sea, west France.