mu·tu·al·ism 
(mych-ə-lĭz′əm)
(mych-ə-lĭz′əm)n.
An association between two organisms of different species in which each member benefits.
mutu·al·ist n.
mu′tu·al·istic adj.
mutualisma clownfish is protected by a sea anemone, which stings the fish's predators; in turn, the clownfish removes parasites from the sea anemone