Carries its poison in a raised horn and holds it out where a fish will bite first.
A large dorid to about 15 cm, orange to pink with a scatter of purple-red spots ringed in white, and a mantle drawn out into lobes along each side and into a single raised horn behind the gill. The rhinophores and gill are the same orange as the body. Ceratosoma tenue is the species most often confused with it and has a broader, more flared mantle skirt and a differently proportioned horn.
The horn is the interesting part. The animal concentrates defensive compounds taken from its sponge food in the mantle margin and particularly in that horn, and it positions the horn towards a source of disturbance — so the part a predator is most likely to bite is the part loaded with the deterrent, and the loss of a piece of mantle costs the animal little. Feeds on sponges and is often found on or beside the one it is eating. Recorded from about 3 to 30 m. Large, slow and conspicuous, and one of the more straightforward nudibranchs to photograph well.
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.
