A large sea hare with dark rings on a pale body, grazing algae in shallow water. It releases purple ink when handled.
Between about 25 and 41 cm; sea hares are soft and stretch, so a maximum length is inherently loose. A big soft humped slug with prominent ear-like rhinophores and large flaps along the sides. The ground colour runs from pale grey through olive to dark brown, with a network of fine black lines and, as the identification, large discrete black rings over the body and flaps. The internal shell is thin, hatchet-shaped and pale.
Other Caribbean sea hares are separated by those bold black rings. There is also an identical-looking Indo-Pacific animal, and the honest answer is that the two can be separated only by where they are and by genetics.
It grazes seaweed in seagrass beds, tide pools and shallow rubble, usually between the surface and 15 m though it has been recorded to 40. When disturbed it releases purple ink. Its skin is leathery and chemically defended, so almost nothing eats it, and it is often out in the open in daylight in the shallows. Mating chains occur.
The Australia record has been removed. Genetic work split this species: the Indo-Pacific animals, including all the Australian ones, are a different species described in 1830, and this one is confined to the Atlantic. It has invaded the Mediterranean, first recorded there in 2002.
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.
