(Quatrefages, 1845)
Description:
This delicate species with an oval body may reaches a length of up to 22 mm and a width of 13 mm. The colour is whitish or yellowish, especially along the margins, or brown blending at margins into a band of bluish-grey; the mid-dorsal line and the lateral branches are brownish or carmine. The marginal tentacles are well developed. Each of the tentacles is speckled with about 50 eyes; the cerebral eye clusters contain about 20-30 eyes each and they may be confluent anteriorly. The mouth is situated anteriorly to or beneath the cerebral organ. The intestinal trunk opens posteriorly through a median pore and possesses three or four pairs of lateral branches, which ramify without anastomosing (O. sanguinolentus-diagrammatic). The hinder end of the intestinal trunk ends in a dorsal anus.
The male and female copulatory organs are ventral to the pharynx. The uterine canals separate posteriorly, each with one to four uterine vesicles.
Habitat:
Under stones in the intertidal zone, among red algae and Laminaria holdfasts, dredged on shells and sandy mud in depths to 60 m.
Distribution:
Ranges from Scandinavia to western Mediterranean. Reported also from Wales and Firth of Clyde, Channel Islands, Plymouth Sound, Isle of Man and various Irish localities.