Coral polyps, the organisms responsible for constructing reefs, are related to sea anemones and jellyfish, thus placing them under the kingdom Animalia. The base of the coral polyp features its protective limestone skeleton, which forms coral reefs.
The reef is expanded when the coral polyp attaches to a rock on the sea floor and clones itself, producing thousands of buds that connect to each other and form a colony. The colonies expand over centuries and eventually join with foreign colonies, becoming reefs. Although coral polyps are translucent animals, the color of the reefs they form is due to the presence of algae housed within the structure.