The three-lined blue phyllidiid, and the one varicosa is most often confused with.
A firm-bodied phyllidiid to about 5 cm, blue-grey to nearly white, with three black longitudinal lines — one down the midline and one along each side — that break and rejoin along the length of the back. Low rounded tubercles stand between the lines and are tipped yellow, and the rhinophores are yellow to orange. There is no gill plume; the family breathes through folds beneath the mantle margin, which places any animal of this shape at once. Phyllidia varicosa is the usual confusion and grows to about twice the size, with the tubercles fused into continuous yellow-topped ridges and the black confined to the troughs between them rather than drawn as flat lines. Phyllidia elegans carries pink-based tubercles on a darker ground.
Feeds on sponges and secretes the terpenes taken from them through the skin, which is why an animal this conspicuous grazes in the open in daylight with nothing following it. The compounds are potent enough that phyllidiids confined with fish in a small volume of water have killed them, and the family has a distinct smell out of the water.
Recorded from about 3 to 30 m on sponge-covered rubble and rock. Worn animals in which the black lines have fused into a single broad band are the ones that take time, and the tubercle tips are usually a better guide than the lines.
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.
