Posterior margins of pleosome segments 1 and 2 with a prominent dorsal tooth. Posterodistal angle of epimeral plate 3 with a small tooth, posterior margin coarsely serrate and deeply emarginate proximally. Head with prominent rostrum, lateral lobes small and angular; eyes large, especially in male, rounded-oval. Antenna 1 about half body length, flagellum up to about 25-articulate, inner margin setose. Antenna 2 in female slightly more than three-quarters body length, peduncle articles 4 and 5 about equal, flagellum very long and slender. Antenna 2 in male as long as body, peduncle very robust, articles 3 to 5 with tufts of short setules on inner margin, flagellum filiform. Gnathopods slender. Gnathopod 1 in female propodus elongate, subrectangular, carpus as long as, or slightly longer than, propodus, palm oblique delimited by 2 or 3 slender spines. Gnathopod 2 in female carpus and propodus of about equal length, propodus oval, palm oblique delimited by slender spine. Gnathopods 1 and 2 in male carpus short, propodus elongate oval, palm almost longitudinal delimited by 2 or 3 slender spines, palmar margin and posterior margin with several small spines. Pereiopods slender; pereiopod 7 especially elongate, basis broad, posterior margin finely serrate. Uropod 3 rami spinose with few short setae, inner ramus expanded proximally, confronted margins minutely toothed. Telson elongate, triangular, apex subacute.
Up to about 7 mm.
Very variable; purplish or whitish, often vividly mottled or marked.
Usually in the shallow subtidal, occasionally intertidal, amongst algae; locally common.
North Atlantic, Arctic Ocean; European coasts from northern Norway and White Sea to the Canary Islands and Black Sea.