A white aeolid the colour of the coral it eats, sitting in the shaded parts of a Porites head.
A soft aeolid to about 3 cm, white to pale cream or tan with rows of short blunt cerata along the back, the whole animal close in colour and texture to the surface of the coral it sits on. There are no bright markings and no contrast to work with, so it is found by shape rather than by colour: a smooth pale lobe on a surface that is otherwise a regular grid of polyps.
It feeds on massive Porites, taking the polyps and the tissue between them, and it does not occur away from the host. A colony that carries the slug usually shows the evidence first, in bare white patches of skeleton and in the egg masses, which are laid as low white ribbons directly onto the dead area. Several animals often share one coral head, and the same head can hold them for months.
Searching the coral is the whole method, and the productive parts are the shaded undersides and the lower flanks of a head rather than the sunlit top. The related Phestilla melanobrachia is a different proposition entirely, being orange to black and living on cup corals. Recorded from about 2 to 25 m wherever massive Porites grows.
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.
