Clownfish and the Anemone
The Clownfish is a tropical reef fish that is primarily know for its role in the Disney movie Finding Nemo.
The Anemone is a very diverse species of coral, some being carnivores, herbivores, or omnivores.
Both organisms benefit from their relationship. The anemone "stings" any organisms that comes within reach, however the clownfish coats itself in a mucus making it invulnerable to the attempts of the coral to consume it, while the anemone benefits because of the clownfish's feeding habits which involve the anemone receiving food that otherwise wouldn't have drifted into its grasp.