Favorinus branchialis

(Rathke, 1806)

This is an unusually variable but always slender and fragile species which may reach 25 mm in overall length. The body is white, frosted superficially by opaque white surface pigment. The cerata are usually pale, with the yellow or pale brown digestive gland lobule showing through the white epidermis, which is interrupted subapically; this distal ring often has an olive-green or brown tinge. The most conspicuous feature is the presence on the dark brown rhinophores of a pale tip which is dilated. Sometimes each rhinophore bears only one bulb, whereas in other specimens there may be two. One individual has been described in which the rhinophore of one side possessed two bulbs while that of the other side had none. Gracefully curved oral and propodial tentacles are present. The colour of the prey affects that of the digestive gland. Both bodily coloration and rhinophoral bulbs may be lacking in the juveniles.

Like Favorinus blianus, this species is known to eat both cnidarians and the eggs of other opisthobranch molluscs (such as Aplysia, Tylodina, Polycera and Archidoris ).

There are not many British records, and these are scattered around the British coasts (Distr. F. branchialis). Further records range from Murmansk and Norway to the Mediterranean Sea, to 20 m.