Dark and finely lined, feeding with the mouth everted into a sea squirt colony.
A polycerid to about 8 cm, the body dark brown to black and carrying many fine cream to yellow lines running the length of the animal, close enough together that from a metre away it reads as dull olive rather than as lined. The rhinophores and the gill plume are dark red-brown to maroon. That colour is the quickest separation from the other Nembrotha on the same ground: N. kubaryana carries orange gills and an orange foot margin, N. cristata green ones, and N. chamberlaini is spotted rather than lined. The one genuinely close is N. purpureolineata, which inverts the scheme — purple lines on a pale ground rather than pale lines on a dark one — so the question to settle is which of the two, ground or line, is the darker.
Feeds on colonial ascidians, and is usually found on or immediately beside a colony with the oral tube everted into it rather than crossing open ground. It takes up the ascidian’s defensive compounds and secretes them in its mucus, which is the usual explanation for a soft animal this size grazing in the open in daylight. Recorded from about 5 to 30 m on the harder ground of a muck site.
The lines are the part of the animal a photograph is likely to lose. They are fine, low in contrast against the dark ground, and a strobe fired straight down the lens tends to flatten them into a black slug; light from the side holds them. Mating pairs and white spiral egg ribbons turn up on the same colonies.
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.
