The largest nudibranch here, and one of the few that swims, by flapping its mantle.
The largest nudibranch in the region and one of the largest anywhere, reaching about 50 cm. Crawling, the mantle is held rolled at the edges and the animal is a red to orange oval with paler mottling; the six gills that give the genus its name sit exposed at the rear. Colour runs from deep blood red through orange to a pale pink in juveniles, and small animals can be nearly white.
Disturbed, or moving between feeding grounds, it lifts off the bottom and swims by unrolling the mantle and flapping it in slow vertical waves — a red sheet turning over in the water, which is what the name describes. Feeds on sponges and lays a distinctive egg mass, a rose-like ribbon of bright red-orange attached on edge to the substrate, which is often found when the animal is not. The commensal shrimp Zenopontonia rex frequently rides on the mantle. Mainly nocturnal; on a night dive it is one of the few animals here that a diver spots from several metres away.
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.
