Underwater image of live coral Montastraea annularis. Note polyp tissue (green) around the mouth and base of the tentacles and zooxanthellae (red fluorescence from chlorophyll) in the tissue between polyps. Tentacles also are visible.
The mushroom coral uses its colorful mouth to feast on adult jellyfish. Unlike reef-building corals, mushroom corals—among the world’s biggest polyps at up to 12 inches centimeters) wide—live as individuals.