Idotea chelipes

(Pallas, 1766)

Body slender. Antenna 1 extending well beyond article 3 of the peduncle of antenna 2; there is a single large aesthetasc, not a pair, at the distal end of the aesthetasc series on the antenna 1. Antenna 2 flagellum longer than the peduncle, about a quarter of the body length. Cephalon subquadrate, eyes dorsolateral, prominent. Coxal plates narrow, only those of pereion segments 5, 6 and 7 reaching the posterior border. Pereiopods all more or less alike. Pleon of two complete segments, and one partial suture in the pleotelson. Pleotelson with the sides subparallel, slightly keeled posteriorly in the mid-dorsal line; posterior border with a single, median tooth, hardly acute, and with obtuse lateral corners. Uropods uniramous.
Males recognizable from about 5 mm body length, ranging to 15 mm; adult females from 6 to 10 mm. Colour mostly uniformly green or brown sometimes with white markings; females often darker than males.

A brackish water species, among intertidal algae in sheltered estuaries or where streams flow over the shore, and also in sheltered brackish pools at or above high water mark.

Recorded from Norway to the Mediterranean, including the Gulfs of Bothnia and Finland.