Coxal plate 2 short and rather angular, posterior angle prolonged especially in male; coxal plate 5 anterior lobe very elongate. Epimeral plate 3 posterodistal angle with minute tooth.
Head, lateral lobe small, angular; eyes moderately large and rounded. Antenna 1 article 3 almost as long as 2, flagellar articles poorly defined, peduncle and flagellum with numerous long setae on posterior margin; accessory flagellum very small. Antenna 2 only little longer than 1, especially robust in male, peduncle article 5 longer than 4, flagellum very short, robust, flagellar articles poorly defined, flagellum and peduncle article 5 often with dense tufts of short setae. Gnathopod 1 propodus oval, narrowing distally, palm strongly oblique, straight, delimited by 2-3 small spines, dactylus with inner margin serrate. Female gnathopod 2 much larger than 1, basis with several long setae on anterior margin, propodus large and oval, palm delimited by 2-3 small spines, palmar margin concave with large angular distal process. Male gnathopod 2 very large, basis short with several long setae on anterior margin, propodus oval in small specimens with small proximal process, in larger specimens propodus elongate with enormous proximal process. Pereopods 3-4 basis, anterior margin with long setae, merus broad with numerous long setae, anterodistal angle produced and overlapping small carpus. Pereopod 5 basis expanded. Pereopods 6-7 robust, basis moderately expanded, posterodistal angle strongly produced and narrowly rounded. Uropods 1-2 outer ramus little shorter than inner; uropod 3 inner ramus straight, outer ramus with hooked apical spine and 2-3 reverted denticles.
Up to 10 mm.
Greyish with distinct reddish brown markings.
Depth range from to metres, found amongst algae, ascidians, hydroid growths, and on rafts, buoys and other fixed and floating objects.
North Atlantic; not previously distinguished from Jassa falcata.