Body broad, dorsoventrally flattened , posterior margins of segments setose; pleon segment 3 produced dorsally into long curved process. especially large in male, with two smaller lateral processes. Coxal plates small, reducing in length from 1 to 7. Head very broad and rounded, rostrum absent, bases of antennae widely separated; eyes well developed, oval. Antenna 1 small, slender, setose, flagellum about 6-articulate; accessory flagellum minute, 2-articulate. Antenna 2 large, robust, very densely setose, larger and more densely setose in male than female, flagellum club-shaped comprising 1 large and 1 or 2 minute terminal articles. Gnathopod 1 small, merus-propodus with setae and pectinate spines, propodus weakly chelate. Gnathopod 2 elongate, more slender than 1, margins with plumose setae, weakly chelate. Pereiopods 3 and 4 sparsely setose, setae simple; pereiopods 5 to 7 broad, posterior margins densely fringed with long plumose setae.
Uropods very dissimilar: uropod 1 biramous, peduncle elongate, rami short; uropod 2 peduncle foliaceous and densely setose, rami flattened and setose in male; uropod 3 extremely large, inner ramus minute and obscured, outer ramus flattened, spinose, in male extremely elongate, in female shorter and more oval. Telson small, triangular.
Up to 6 mm.
Depth range from about low-water to a few metres. These amphipods burrow into submerged and waterlogged timber which has already been attacked by the wood-boring isopod Limnoria .
North Atlantic, American and European coasts; North Sea; Mediterranean; Black Sea; very widespread. Also from southern hemisphere, South Africa, Australia, New Zealand.