Okenia quadricornis

(Montagu, 1815)

The body of this species reaches 22 mm in length, red or yellow in colour, speckled with orange and brown. There are two pairs of long, tapering, anteriorly directed pallial papillae in front of the rhinophores and up to four pairs of shorter processes alongside the gills. The rhinophores each bear numerous (up to 35) fine lamellae. There are up to twelve simple pinnate gills, forming a circle around the anal papilla.

The diet consists of ascidians such as Molgula occulta and perhaps Ascidiella aspersa .

The species has been recorded from the Shetlands, the North Sea and the Celtic Sea, as well as in the western English Channel, to 60m (Distr. O. quadricornis). Elsewhere it is known from Norway to the French Biscay Coast (as far south as Arcachon).