Rostrum straight, apex occasionally bifid; four to six dorsal teeth (rarely one to three, seven or eight), two ventral teeth (rarely none, one, three or four); one of the dorsal teeth behind the posterior edge of the orbit.
Carapace with antennal and branchiostegal spines. Antennules triramous; shorter ramus of outer flagellum about 0.8 x length of peduncle and fused for about 0.75 of its length to the longer ramus. Outer edge of stylocerite slightly convex, anterior border straight, apical spine short and stout.
Scaphocerite extends into proximal half of propus of pereiopod 2 (or to 0.5 of length of dactyl in juveniles), apical spine not exceeding lamellar portion. Third maxilliped extends to little over half length of scaphocerite; exopod present.
Mandible with incisor and molar process, but without palp. Dactyl of pereiopod 2 little over 0.33 x length of propus; carpus about 1.2 x length of merus, but occasionally up to 1.7 x merus length.
Telson with two pairs of lateral spines.
Length up to 50 mm, usually less.
Almost transparent and consequently difficult to see in the field. Under magnification, small brownish-black pigment spots are visible.
Shallow water; hyperbenthic species, may swim up at night. A brackish water species, often found in shallow saltmarsh pools. Other brackish ponds and lagoons that have indirect communication with the sea. Never found in fully marine conditions.
Distribution in the North Sea:
All North Sea.
Ranges from the west Baltic and British isles southwards to the W Mediterranean.