Corals produce specialised tentacles such as sweeper tentacles which are armed with powerful stinging cells known as nematocysts. These nematocysts are capable of digesting the tissue of their neighbour if they come in contact. An aggression hierarchy has been identified among corals, and often the slower growing species are the most aggressive.

The false coral (corallimorph) Discosoma is attacking a colony of lettuce coral Agaricia agaricites.