The clownfish hides in the stinging tentacles of a sea anemone. The latter gains nothing from the relationship. The former gains a place to hide from predators. There are several theories why the clownfish does not get stung and therefore eaten. One of them is that the clownfish excretes a mucus that protects it. Another points to the fact this coexistence has been that way for millions of years, time enough for adaptations to be made and passed on to future generations such as a strong tolerance to venom, as in certain snakes that prey on venomous snakes.
