Aplysia parvula

Scientific name : Aplysia parvula

Sea hare highly variable in colour, that can be yellow, grren or (like here) black with white borders. The edges of the parapodia (the side expansions of the foot, used to swim) make a tuft over the back. 6 cm
There are many similar Aplysia species, identification is not always easy.
If disturbed secretes a large amount of a purple fluid, probably only to generate confusion in the predator.

Associated organisms
With its food seaweeds.