This is a long fish with a short, pointed tail. The dorsal papilla are united in groups of between three and nine and emerge from short lateral appendages (6 - 9 each side). The head has a pair of long smooth tentacles. The rhinopores are similar but have easily seen rings (17 - 22). Violet flabellina are usually purple and are darker at the front. In transparence the digestive system and the large reddish hepatic gland that extends to the dorsal papilla can be seen.
This species feeds exclusively on the hydroid Eudendriumdieta and may easily be found amongst the colonies. They have developed an amazing technique whereby they can eat the hydroids without triggering the stinging cells, which remain intact and migrate through the stomach wall and into colourful projections on the back of the nudibranch. Here the stinging cells become embedded in the skin of the nudibranch and are ready to sting a fish or other predator which may try to eat the nudibranch! So the nudibranch uses the defence mechanism of the hydroid to protect itself from predators. Reproduction takes place between March and September.