Takes its colour from the cup coral it eats, and is found nowhere else.
An aeolid to about 5 cm with a dense cover of soft cerata over the back and smooth rhinophores. Colour follows the food: animals on black-brown Tubastraea colonies are black-brown, animals on orange colonies are orange, and the pigment is taken from the coral rather than made by the slug. Against the closed polyps it is very hard to pick out, and the coiled egg strings laid on bare skeleton between the polyps are often noticed first.
It feeds only on Tubastraea, the non-photosynthetic cup corals that grow under ledges and on wreck plating and jetty pilings, and it does not occur away from them. A heavily worked colony shows bare skeleton where polyps have been eaten out. Other Phestilla feed on Porites and Goniopora and are separated largely on which coral they are sitting on, since the animals themselves are similar in build.
Recorded from about 3 to 30 m wherever the coral grows. As much a night find as a day one, since the polyps are open after dark and the slug is out among them rather than tucked into the base of the colony.
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.
