Ancula gibbosa

(Risso, 1818)

The body is white, elongated and slender, up to 33 mm in length. At the level of the gills the mantle is produced on either side into strong, dorsally directed, pallial tubercles (up to seven on each side). A pair of similar but more slender tubercles project forward from each rhinophore stem and the sides of the head are produced into short, finger-like oral tentacles. All these processes are usually tipped with yellow or orange. Occasional all-white individuals have been reported. The rhinophores each bear up to twelve lamellae. The gills are tripinnate, three in number, protected by the defensive pallial papillae.

This species is of sporadic occurrence on shores and in shallow waters all around the British Isles, feeding upon tunicates such as Botrylloides leachi, Botryllus schlosseri andDiplosoma listerianum. It may be on the decline in Britain, since the mid-nineteenth century, when Alder & Hancock reported that it was one of the most abundant nudibranchs of the Northumberland coast.

A. gibbose has one of the widest geographical ranges of any nudibranch of the north Atlantic (Distr. A. gibbosa). Recorded first from the western Mediterranean near Nice, it also occurs along the European Atlantic coast from the Bay of Biscay to the White Sea and Murmansk. There are also reliable reports from the Faeroes, Iceland and west Greenland, and from the New England American coast. The deepest records are from 110 m.