Idotea pelagica

Leach, 1815

Body short and stout. Antenna 1 extending well beyond article 2, but hardly beyond article 3 of the peduncle of antenna 2. Antenna 2 very robust; flagellum shorter than the peduncle, less than 1/6 of the body length and with pads of fine setae in adult males.
Cephalon subquadrate, eyes dorsolateral, prominent. Maxillipedal palp of four articles. Coxal plates fairly broad, widening posteriorly and reaching the posterior border of pereional segments 4 to 7.
Pereiopods all very robust, the terminal claw being relatively larger than that of any other Idotea species; adult males with pereiopods 2-7 fringed with pads of fine setae on their inner surfaces.
Pleon of two complete segments, and one partial suture in the pleotelson.
Pleotelson broadly rounded, apical border having a short, median, obtuse tooth; not keeled.
Uropods uniramous.
Colour merges well with typical background of barnacles, mostly dark purple-brown, with white diamond-shaped patches or elongated stripes down the mid-dorsal line, and with white markings along the edges of the dorsal side; females often darker than males.

Resident on exposed shores among barnacles and stunted fucoid algae. Also (occasionally) free swimming.

Males up to 11 mm; females 7-10 mm.

Depth range

Distribution in the North Sea
All North Sea.

World distribution
Recorded from Norway to the French coast; not in the low salinity waters of the inner Baltic.