Deep blue-black with electric blue lines, and it is on somebody else's menu.
A polycerid to about 7 cm, very dark blue to black, marked with fine iridescent blue lines along the sides and around the mantle edge and with blue-green rhinophores and gill. The body is firm and the profile is high-shouldered. The colour is subtle enough that the animal reads as plain black until a light is put on it from the side.
Feeds on bryozoans — moss animals — from which it takes tambjamines, a group of pigmented alkaloids that are both its colour and its defence. Those compounds are the reason it is eaten by very little, and the reason it is eaten by Roboastra, which specialises in slugs that carry them and is unaffected. A Tambja attacked by a Roboastra will release a cloud of the pigment and try to escape, which for a sea slug is a fast business. Recorded from about 5 to 35 m on hard ground.
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.
