Mutually beneficial friendship

In nature, there is often a mutually beneficial friendship. Here is one example: clown fish and actinia.

This fish lay in the actinia for about an hour.

It's reported that an actinia does not sting a clown fish because of its special mucus. Scientists even created a cream based on this mucus. And what is the use of an actinia from a fish clown? Fish clowns attract other fish to actinia, which become lunch for actinia.

Thank you @juliank @photocontests for the contest.