Unlike other cnidarians, the sea anemones and corals do not have a medusa stage in their life cycle. Their eggs form larvae which attach to some surface and start developing a new animal or colony. Each animal or polyp have a cylindrical body and one or more rings of tentacles around the mouth. Some anthozoans have the ability of both sexual and asexual reproduction.
The anthozoans are divided into two subclasses. The members of Hexacorallia, like sea anemones, tube anemones and stony corals, have a sixfold radial symmetry. The number of tentacles, for instance, often come in a plural of six. The other subclass, Octocorallia, include species like soft corals and sea pens, with an eightfold symmetry.