Ploughs through soft sediment after sea pens, and surfaces only to move on.
A sea slug to about 10 cm, the back carrying fine longitudinal ridges of white or cream on a dark grey to black ground, with an orange to yellow band around the mantle margin and along the foot. The body is flattened and firm, the rhinophores short and set at the very front, and there is no gill plume on the back — the gills are hidden under the mantle skirt, which is what separates the arminids from the dorids at a glance.
A burrowing animal, which is unusual for a nudibranch. It spends most of its time under the surface of soft sediment and is generally seen at night, crossing open silt between one patch and the next, leaving a shallow furrow behind it. It feeds on sea pens and soft corals buried in the same sediment. Recorded from about 5 to 30 m. Some Armina are strongly bioluminescent when handled; that is not a reason to handle one. The animals surface and submerge on their own schedule, so a slug found half-buried is best left to finish emerging rather than uncovered.
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.
