Body robust, smooth; coxal plates moderately large, plate 1 rounded anteriorly. Epimeral plate 3 quadrate, posterior margin weakly crenulate. Head with broadly rounded lateral lobes; eyes large, oval. Antenna 1 robust, half the body length, peduncle articles 1 and 2 about equal in length, article 3 half the length of article 2, flagellum setose, shorter than the peduncle in female, little longer in male; accessory flagellum small, 2-articulate. Antenna 2 much shorter than antenna 1, slender, peduncle articles 4 and 5 about equal. Basis of gnathopod 1 robust, propodus oval, little longer than the carpus, both strongly setose, palm oblique, convex, delimited by 2 small spines. Female gnathopod 2 much larger than gnathopod 1, carpus with the posterior margin very densely setose, propodus oval, setose, palm oblique delimited by a small spine, palmar margin spinulose. Male gnathopod 2 very large and robust, basis broad and angular, carpus short with a slender setose posterior lobe, propodus elongate oval, strongly setose, palm longitudinal with 2 small marginal teeth and a large truncated lobe close to the base of the dactylus, dactylus short and strongly curved. Pereiopods 5 to 7 broad and robust, basis with a large posterior lobe, posterior margin setose, dactylus small. Uropods 1 and 2 spinose; rami of uropod 3 broad, truncated distally, spinose, outer ramus slightly longer than the inner one. Telson deeply cleft, each lobe rounded apically with a small group of submarginal spines.
Up to about 10 mm.
Variable, yellowish, sometimes speckled with violet, or violet with white patches.
Depth range from about 0 to 100 metres; often amongst algae in shallow subtidal habitats; locally common.
Widespread; North and South Atlantic; Indian Ocean; Pacific Ocean; Red Sea; Mediterranean; North Sea and around British Isles; Atlantic coast of Europe to Skagerrak.