A big soft orange slug with a single gill down its right side, and acid in its skin.
A large, soft-bodied slug to about 20 cm, orange to red-brown, the back covered in low polygonal tubercles arranged in a mosaic, with two rolled rhinophores at the front and an oral veil below them. It is not a nudibranch: pleurobranchs carry a single feathery gill on the right side of the body between the mantle and the foot, and many retain a thin internal shell.
Nocturnal, and one of the larger animals to appear on rubble and silt after dark, where it feeds on colonial ascidians. Several species in the genus secrete mucus with a very low pH — sulphuric acid has been measured in some — as a defence against fish and against being handled, which is why they are left alone by almost everything. Disturbed animals can swim briefly by flapping the mantle. Recorded from about 3 to 30 m, and one of the finds that makes a night dive over apparently empty ground worth making.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
