Sea anemone

Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria. They are named for the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Hexacorallia. Anthozoa often have large polyps that allow for digestion of larger prey and also lack a medusa stage. As cnidarians, sea anemones are related to corals, jellyfish, tube-dwelling anemones, and Hydra.

Many sea anemones form symbiotic relationships with single-celled dinoflagellates, whether zooxanthellae or zoochlorellae, that live within their cells.

The global trade in marine ornamentals for aquariums is rapidly expanding, and threatens sea anemone populations as the trade depends on collection from the wild, and the animals grow and reproduce relatively slowly.

Anatomy

A sea anemone is a sessile polyp attached at the bottom to the surface beneath it by an adhesive foot, called a basal disc, with a column-shaped body ending in an oral disc. Most are from 1.8 to 3 cm (0.71 to 1.18 in) in diameter, but anemones as small as 4 mm (0.16 in) or as large as nearly 2 m (6.6 ft) are known. They can have from a few tens to a few hundred tentacles.