Polycera quadrilineata

(Müller O.F., 1776)

This common species may reach a length of 39 mm, coloured white with yellow or orange pigment located in blotches. There is usually a row of ovoid blotches down the midline of the back together with others on the flanks and the dorsal metapodium. Occasionally, streaks and blotches of jet black may be present. On either side of the gill circlet, the mantle rim is produced into a strong, posteriorly directed yellow or orange tipped papilla or tubercle. Similar conspicuous tubercles project from the frontal margin of the head, usually four in number, rarely up to six (P. quadrilineata-drawing). The rhinophores, propodial tentacles, oral lobes and the simple pinnate gills (up to 11 in number) are tipped with yellow.

The preferred diet consists of encrusting bryozoans, especially Membranipora membranacea , but also Electra pilosa , Callopora dumerilii , Celleporella hyalina and Tegella unicornis , usually on the lower shore, or in shallow offshore situations, to 60 m.

It is common all around the British Isles and has also been recorded from Helgoland, Greenland, Iceland, Faeroes, and the European coast from Norway to the Mediterranean Sea (as far as Naples), to 160 m (Distr. P. quadrilineata).