The actual animal that makes up the physical coral is called a polyp. It is column shaped and attaches itself to the floor of the reef. The top end extends into the water and is free to move about. Thousands of individual polyps form a colony, which in turn forms a reef. Each individual polyp is responsible for each bump in the reef.
Polyps are active at night.
During the daytime, they retreat into their skeleton, so divers usually only see their skeletons. Because of warm water and abundant food supply, coral reef communities are bustling with life. Reefs with their bush like shape offer many nooks and crannies for fish to hide in. Small fish can hide from big predators inside a coral reef. Because of this, many small tropical fish are found in coral reefs.