(M. Sars, 1858)
Body markedly tumid, extremely robust and rugose; anterior pereion strongly arched; posterior pereion and pleon carinate; pereion segment 7 and pleon segments 1 to 3 each with a prominent backwardly directed dorsal keel and a pair of lesser dorsolateral ridges; pleon segment 4 with a distinct mid-dorsal notch and a pointed keel. Coxal plates 1 to 3 narrow, pointed distally; plate 4 strongly developed and much longer than plate 5, distal angle and posterior angle acute; plate 6 with a tooth on the posterior margin. Epimeral plate 3 with one big tooth on the posteriodistal corner. Head with an elongate rostrum, weakly curved; eyes very large, pear-shaped. Antenna 1 peduncle article 1 equal to 2 and 3 combined, flagellum about twice as long as the peduncle, about 20-articulate. Antenna 2 little longer than antenna 1, flagellum twice as long as the peduncle, multi-articulate. Gnathopods slender, subchelate; carpus as long as the propodus. Pereiopods 3 and 4 slender. Basis of pereiopods 5 and 6 robust, scarcely expanded. Basis of pereiopod 7 twice as long as broad, with a small posterodistal tooth. Uropod 3 rami lanceolate, spinose. Telson longer than wide, apex notched.
Up to about 9 mm.
Parasitic on the echinoderms Parastichopus tremulus and Porania pulvillus .
North Norway, North Sea, Oslofjord, Skagerrak down to Bay of Biscay.