Body especially slender in male. Coxal plates 1 to 4 about equal in length in male, in female slightly increasing in length from plate 1 to 4. Lateral lobes of the head broadly produced, apex acute; eyes moderately large, rounded-oval. Antenna 1 about one-third of the body length, peduncle article 3 much longer than article 1 and slightly shorter than article 2, flagellum about 7-articulate; accessory flagellum small, distinct, 2-articulate. Antenna 2 in male much longer than antenna 1, peduncle elongate, robust, flagellum about 5-articulate; in female antenna 2 much less robust and only little longer than antenna 1. Gnathopod 1 basis with a small anterodistal lobe, carpal lobe broad, propodus oval, palm strongly oblique, convex, margin finely crenulate, delimited by one or two slender spines.
Male gnathopod 2 basis long with a large distal lobe. ischium also lobed, propodus extremely large, elongate, often weakly curved, palm straight or concave, longitudinal, densely setose, parallel with anterior margin, distal margin of the palm with a small truncated process, dactylus short and very robust. Female gnathopod 2 generally similar to gnathopod 1, slightly larger, carpal lobe narrow. palmar margin weakly sinuous. Pereiopods 3 to 7 relatively much longer in male than in female. Uropods 1 and 2 spinose, outer ramus little shorter than inner one; uropod 3 peduncle very elongate, outer ramus with the distal margin with group of minute reverted denticles. Telson triangular, apex acute.
Length about 5 to 10 mm, occasionally up to 15 mm.
Variable, yellowish green, speckled with dark pigment, or whitish, with brown transverse bands.
Depth range from the low-tide level to 200 metres, constructs tubes amongst algae or hydroid; occasionally found intertidally in low-level rock pools. May be locally common; often as fouling organism on pilings, buoys, etc.
Circumpolar; widely distributed in the Arctic Ocean, North Atlantic and adjoining seas. South Baltic to Iceland.