Anthozoa

Sea anemones and corals belong to the class Anthozoa within the phylum Cnidaria. Unlike other cnidarians, anthozoans do not have a medusa stage in their development. Instead, they release sperm and eggs that form a planula, which attaches to some substrate. Some anthozoans 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 dinoflagellates called zooxanthellae. While there is some dispute over whether this is a commensalistic or mutualistic relationship, it does appear mutualistic. The zooxanthellae are provided with protection by the anthozoan; it takes up wastes and carbon dioxide and provide their host (anemone or coral) with carbohydrates and oxygen. It's these zooxanthellae that give anemones and corals their color.