Pleon segments 1 to 4 each with a dorsal tooth; in male and small female dorsal teeth quite small on segments 2 and 3 and almost or absent on segment 1. Head with weakly angular lateral lobes; eyes moderately large, rounded-oval, larger in male than in female. Antennae about equal in length in female, antenna 2 much longer than antenna 1 in male; antenna 1 peduncle article 1 without a distal tooth; antenna 2 peduncle articles 4 and 5 in male with tufts of short fine setules. Propodus of female gnathopod 1 almost as broad as long with groups of strong setae on the anterodistal margin, palm almost transverse, minutely toothed, delimited by a pair of slender spines. Male gnathopod 1 similar to female except for the anterior margin of the propodus with a deep cleft. Gnathopod 2 little longer and more slender than gnathopod 1, propodus narrow proximally, sparsely setose, palm oblique, minutely toothed. Basis of pereiopod 5 with a narrow posterior lobe; basis of pereiopod 6 broadly expanded; basis of pereiopod 7 slender, not expanded; pereiopods 5 to 7 strongly spinose. Coxal gills weakly pleated. Rami of uropod 3 a little longer than the peduncle, spinose and with few setae. Telson elongate, cleft almost to the base, each lobe with a few dorsolateral spinules.
Up to about 5 mm.
Variable, often greenish yellow speckled with white.
Depth range from the intertidal to about 30 metres, locally abundant; usually amongst algae. hydroids, sponges, or beneath stones and rocks.
Boreal North Atlantic, American and European coasts; Iceland, Faroes; from Norway to north west France; also recorded from the western Mediterranean.