Class Anthozoa includes coral polyps and sea anemones. They are called "flower animals" due to their flower-like appearance, with tentacles radiating from their bodies like petals and often being brightly colored. Coral polyps secrete cups of limestone for protection, which grow together over large colonies to form coral stone reefs that harbor tremendous biodiversity, comparable to tropical rainforests. Coral polyps photosynthesize through symbiotic algae called zooxanthellae and require warm, clear, shallow water for the algae to survive, providing 90% of the corals' diet.