Body oblong. Cephalon subquadrate, with a marked transverse sinuous furrow behind the eyes. Eyes large and bulbous. Antenna 1 hardly extending beyond article 3 of the peduncle of antenna 2; antenna 2 robust, flagellum shorter than peduncle and about 1/6 the length of the body. Maxillipedal palp of four articles. Coxal plates triangular, extending over the whole length of the segment in pereion segments 2 or 3 to 7; segments 5 to 7 sharply produced laterally. Pereiopods all more or less alike. Pleon of two complete segments, and one partial suture in the pleotelson. Pleotelson with the sides and posterior border straight. Uropods uniramous.
Length in males recognizable from about 8 mm, ranging to about 30 mm; females from 9 to 18 mm. Colour is uniformly greyish or brown.
Among floating weed, timber and colonies of Lepas carried by the Gulf Stream and North Atlantic Drift.
This species occasionally reaches the North Sea from the east coast of North America.