noun, plural: sea anemones
Any of the animal species belonging to the order Actinaria of class Anthozoa, and characterized mainly by their colorful sessile polyp typically attached at the substrate through a basal disc, and an oral disc surrounded by stinging tentacles (which when expanded, resemble the petals of a flower)
Sea anemones belong to the order Actinaria of the subclass Hexacoralia. Hexacorallia is a subclass of the calss Anthozoa. This subclass includes not only the sea anemones but also stony corals, tube anemones, and zoanthids.
Sea anemones have oral disk surrounded by one or more circles of simple tapering tentacles, which are often very numerous, and when expanded somewhat resemble the petals of flowers, with varied colours. Their name is derived from their resemblance to the terrestrial flower, anemone. The tentacles have cnidocytes that are used for defense and capturing prey (e.g. small fish and shrimp). The opening in the middle of the oral disc serves both as a mouth and an anus. They have an adhesive foot referred to as basal disc, which helps them to attach at the bottom to the surface. Their diameter typically ranges from 1.8 to 3 cm. Few of them though are not attached to the bottom and have a gas chamber within the pedal disc that allows them to float up and down the water column.1
Similar to the stony corals, the sea anemones form symbiosis with algal species, such as zooxanthellae (dinoflagellate endosymbionts) and zoochlorellae (green algal endosymbionts). These algal species live within their cells.
- Kingdom: Animalia
- Phylum: Cnidaria
- Class: Anthozoa
- Subclass: Hexacorallia
- Order: Actiniaria
1 Barnes, R. D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 150–157.