Large colonies are found in some warm, shallow waters, where colonies of millions of coral polyps form vast coral reefs. It settles on a hard support and will never move again. The soft body of a coral polyp is about the size of a pencil eraser. The polyp of hard corals makes a hard, protective shell out of calcium carbonate. When the polyp dies, the chalky skeleton remains, and another polyp will grow on top of the old one.
Coral colonies grow in many shapes and come in many colors.
Many corals have symbiotic algae that live inside them.