Sea Anemone

Lore & Background

A 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. The polyp has a columnar trunk topped by an oral disc with a ring of tentacles and a central mouth. The tentacles can be retracted inside the body cavity or expanded to catch prey. They are armed with cnidocytes (stinging cells). Many species gain additional nourishment from a symbiotic relationship with single-celled dinoflagellates, zooxanthellae, or green algae (zoochlorellae) that live within their cells. Some species live in association with clownfish, hermit crabs, small fish, or other animals to their mutual benefit.

Reader's Guide

Sea anemones breed by liberating sperm and eggs through the mouth into the sea. Fertilized eggs develop into planula larvae that are planktonic for a while before settling on the seabed and developing directly into juvenile polyps. They also breed asexually by breaking in half or into smaller pieces that regenerate into polyps. Sea anemones are sometimes kept in reef aquariums; the global trade in marine ornamentals for this purpose is expanding and threatens sea anemone populations in some localities, as the trade depends on collection from the wild.

Did You Know?

• Some sea anemones can exceed 1 meter in diameter, such as Urticina columbiana and Stichodactyla mertensii.
• Clownfish are not affected by their host anemone's sting and shelter among its tentacles.