Body oval in outline, readily rolling into a ball. Antenna 1 with 2 to 8 aesthetascs. Maxillipedal palp with prominent lobes fringed with smooth setae on articles 2 to 4. Five anterior pleon segments all fused; sixth pleon segment fused with the telson as a pleotelson which articulates freely with the pleon. Coxal plates of pereion segments 2 to 7 fused with the segments. Pereiopod 1 ischium with up to 30 smooth setae, merus with up to about 20, and propus distal row with 2 (occasionally 1). Pleotelson rounded or only slightly acute at the apex, without a mid-ventral respiratory channel and posterior border not notched. Pleotelson dorsal surface covered with very small tubercles; extending beyond uropods in adult males. Uropods lateral, with the expod and endopod subequal in length, endopod rounded at the apex. Uropod with the outer edge of the exopod almost smooth. No sexual dimorphism.
Sexes recognizable at 3 to 3.5 mm body length, males reaching 10.0 mm and females 7.5 mm.
In sheltered estuarine situations, usually in salt marsh pools, often burrowing but also in crevices or under stones and driftwood between HWS-MTL near the limits of tidal influence.
Apart from a single record in Morocco the range of this species is from the Bay of Biscay northwards to northern Scotland and then eastwards into the southern Baltic as far as southeast Sweden.