Sea hare

Sea hares are big, soft, shell-less molluscs that look rather like a wet slug with rabbit ears, which is where the name comes from: the two "ears" are rhinophores, chemical sensors, and a second pair of tentacles sits lower on the head. Along the back are two large fleshy flaps, the parapodia, which some species flap to swim in a clumsy, undulating way. Colour ranges from olive and brown to almost black, usually mottled and often edged in a paler line, and the animal takes its shade from the algae it eats. Common Maltese species include Aplysia depilans, Aplysia fasciata and Aplysia punctata; the spotted sea hare Aplysia dactylomela, an Indo-Pacific arrival that reached the Mediterranean in 2002 and Malta by 2008, is marked with black-ringed spots on a paler ground.

They are grazers, working through green and red algae in very shallow water, and around Malta and Gozo you meet them from the surface down to about 10 m, on algae-covered rock, on sand between weed and along the shallow edges of Posidonia meadows. Big Aplysia depilans can reach 40 cm and a solid weight, which is a surprise the first time you find one.

The defence is the memorable part. Handled or attacked, a sea hare releases a cloud of purple ink from one gland and a sticky white opaline secretion from another. The purple comes from pigments in the red algae it has eaten, and the mixture works by jamming a predator's sense of taste and smell rather than by poisoning it.