Body smooth and laterally flattened ; coxal plate 1 not produced forwards, plates 2 to 5 rounded, posterodistal margins with a few long setae; epimeral plates 1 to 3 rounded. Lateral lobes of head broadly rounded; eyes moderately large, rounded. Antenna 1 much longer than antenna 2, about half the body length, peduncle short with article 1 robust and slightly longer than article 2, article 3 very small, flagellum long and slender, up to 30-articulate. Antenna 2 peduncle articles 4 and 5 about equal in length, flagellum quite short, setose, up to 15-articulate. Gnathopod 1 small, basis with a small anterodistal lobe, propodus rectangular, setose, palm transverse, convex, dactylus much longer than the palm. Female gnathopod 2 similar to gnathopod 1 except that it is slightly larger and with the carpal lobe more slender. Male gnathopod 2 extremely large, carpus very short, propodus massive, elongate, palm extending the entire posterior margin, sparsely setose, with a large tubercle close to the base of the dactylus, palmar margin minutely crenulate, dactylus massive reaching the entire length of the propodus, with the inner margin sinuous and setulose. Pereiopods 3 and 4 merus expanded; pereiopod 5 basis very broadly expanded; pereiopods 6 and 7 basis with only a narrow posterior lobe, propodus only weakly expanded distally. Uropods 1 and 2 spinose, outer ramus slightly longer than the inner one; uropod 3 outer ramus with the dorsal margin finely toothed and with two strong apical hooks, inner ramus with one or two apical spines and several setae; uropod 3 peduncle inner distal margin with four or five short spines, outer distal margin with a group of long setae. Telson short, broad, apex truncated between lateral cusps.
Up to 10 mm.
Greenish yellow, or yellowish with red markings.
Intertidal and in the shallow subtidal on algae; also described as epipelagic since it is often cast up with Sargassum along parts of the American coastline.
North Atlantic, American and European coasts; a southerly species ranging from the Sargasso Sea to western Norway.