Mature female more or less asymmetrically pyriform; with distinct segments on the pereion and pleon. The postero-lateral border of the maxillipede has two short processes, and the posterior process of oostegite 1 is rounded and incurved. Pereional lateral plates present but often small; not contiguous. Sides of the pleon segments prominent and rounded; five pairs of pleopods, which are biramous and lanceolate; pleopods tuberculate projecting laterally when seen from above. Uropodal segment very small, uropods lanceolate. Oostegites completely enclosing the brood chamber. Males with the pleon of unfused segments.
Females about 10 mm long, males 2 mm.
Parasitic in the branchial cavity of the hermit crab Pagurus bernhardus .
Records from the Kattegat, Norwegian coast and south-west coasts of the British Isles.