Anthozoa is a class of marine invertebrates which includes the sea anemones, stony corals, soft corals and gorgonians. Adult anthozoans are almost all attached to the seabed, while their larvae can disperse as part of the plankton.

The basic unit of the adult is the polyp; this consists of a cylindrical column topped by a disc with a central mouth surrounded by tentacles.

Sea anemones are mostly solitary, but the majority of corals are colonial, being formed by the budding of new polyps from an original, founding individual. Colonies are strengthened by calcium carbonate and other materials and take various massive, plate-like, bushy or leafy forms.

Unlike other members of this phylum, anthozoans do not have a medusa stage in their development. Instead, they release sperm and eggs into the water. After fertilisation, the planula larvae form part of the plankton. When fully developed, the larvae settle on the seabed and attach to the substrate, undergoing metamorphosis into polyps. Some anthozoans can also reproduce asexually through budding or by breaking in pieces. More than 16,000 species have been described.

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