The grey sea slug can be found around the British Isles and into the colder northern waters of Europe, and despite its name, can be found in a range of colours, including yellow, brown or purple at the base. It has a pair of rhinophores on the head and somewhat longer protruding oral tentacles, which help to sense their surroundings and provide protection. Even though this species is only a quaint 12cm long when fully grown, it can lay up to 400,000 eggs on the underside of a rock, in a pretty ribbon pattern, usually between January and August. The larvae then disperse in plankton once hatched and are usually found in deeper depths until they reach adulthood.