Pure white with a yellow frilled edge, and the mantle ripples the whole time.
A dorid to about 7 cm, translucent white throughout with a broad mantle skirt edged in a band of bright yellow, and with the same yellow on the tips of the rhinophores and around the gill plume. The skirt is thin, deeply undulating and in constant motion, and the name — the genus is from ardea, a heron — records both the white and the movement.
Feeds on sponges. Like the rest of its family it concentrates the sponge’s defensive chemistry in glands around the mantle rim rather than through the body, which is the part a fish would take first. It sits on and beside the food sponge and is generally found on the harder ground at the ends of a muck slope rather than out on silt. Recorded from about 5 to 35 m. A white animal on a dark ground is the classic exposure trap: metered for the sand it burns out, and the yellow border goes with it.
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.
