Coral polyps, stimulated by a near UV light. Initially believed to be a plant, coral is in fact an a

Coral polyps, stimulated by a near UV light. Initially believed to be a plant, coral is in fact an animal. While a coral head appears to be a single organism, it is actually a group of many individual, yet genetically identical, polyps. The polyps are multicellular organisms. Polyps are usually a few millimeters in diameter, and are formed by a layer of outer epithelium and inner jellylike tissue known as the mesoglea. They are radially symmetrical, with tentacles surrounding a central mouth, the only opening to the stomach or coelenteron, through which food is ingested and waste expelled. (Photograph: Mick Gulson)