Anthozoa

Sea anemones and corals belong to the class Anthozoa within the phylum Cnidaria. Unlike other cnidarians, anthozoans do not have a medussa stage in their development. Instead, they release sperm and eggs that form a planula, which attaches to some substrate. Some anthozoa can also reproduce asexually through budding.

Although sea anemones can catch fish and other prey items and corals can catch plankton, anthozoans also rely on a symbiotic relationship with the dinoflagellate, zooxanthellae. While there is some dispute over whether this is a commensalistic or mutualistic relationship, it does appear mutualistic. The zooxanthellae is provided with protection from the anthozoan; it takes up wastes and carbon dioxide and provides its host (anemone or coral) with carbohydrates and oxygen. It's these zooxanthellae that give anemones and corals their color.