Onchidoris sparsa

(Alder & Hancock, 1846)

This flattened onchidorid rarely reaches 8 mm in length; most records have been of animals which did not exceed 5 mm. It adopts a rounded shape when at rest, resembling a small bryozoan colony. The mantle colour is usually pale brown with pink-red blotching. The back bears numerous small rounded spiculose tubercles which sometimes have a basal ring of black pigment together with a terminal black speck. The pigmentation of the mantle around the rhinophores is usually different from the remainder, sometimes darker, sometimes paler, and conspicuous pallial tubercles arise from these areas. Up to ten simple pinnate gills may be present.

This species feeds upon the bryozoans Cellepora pumicosa and Porella concinna .

Scandinavian records of O. sparsa have come from the Swedish Gullmarfjord and the Skagerrak. The most northerly records are, however, from the Orkneys, while collections have been made from scattered localities all around the British Isles. Southwards it reaches its limit on the Spanish Biscay coast (Distr. O. sparsa).