Nembrotha lineolata with its head inside an ascidian. According to Bill Rudman at the Sea Slug Forum, solitary ascidians like this, often known as 'sea squirts', have an outer sac which protects the delicate sieve-like basket which filters their food out of the sea water and encloses the rest of the body. It looks like species of Nembrotha feed on solitary ascidians by inserting their extensible oral tube through one of the siphons to get to the fleshier parts of the body.
