Sea anemones also breed asexually, by breaking in half or into smaller pieces which regenerate into polyps. The resulting fertilized eggs develop into planula larvae which, after being planktonic for a while, settle on the seabed and develop directly into juvenile polyps. Sea anemones breed by liberating sperm and eggs through the mouth into the sea. Some species of sea anemone live in association with hermit crabs, small fish, or other animals to their mutual benefit. In many species, additional nourishment comes from a symbiotic relationship with single-celled dinoflagellates, with zooxanthellae, or with green algae, zoochlorellae, that live within the cells. They are armed with cnidocytes (stinging cells). The tentacles can be retracted inside the body cavity or expanded to catch passing prey. The polyp has a columnar trunk topped by an oral disc with a ring of tentacles and a central mouth. Unlike jellyfish, sea anemones do not have a medusa stage in their life cycle.Ī typical sea anemone is a single polyp attached to a hard surface by its base, but some species live in soft sediment, and a few float near the surface of the water. As cnidarians, sea anemones are related to corals, jellyfish, tube-dwelling anemones, and Hydra. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Hexacorallia. Because of their colourful appearance, they are named after the anemone, a terrestrial flowering plant. Sea anemones are a group of predatory marine animals of the order Actiniaria.
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