Sea anemones are flower-like marine, predatory animals.
They are named after the anemone, a terrestrial flowering plant.
There are more than 1,000 species of sea anemone.
Sea anemones are found from the tidal zone of all oceans to depths of more than 10,000 meters (about 33,000 feet). Some live in brackish water. They are largest, most numerous, and most colorful in warmer seas.
Some species of sea anemone can live more than 50 years.
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 of the water.
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 passing prey. They are armed with cnidocytes (stinging cells).
Sea anemones appear in a remarkable variety of shapes and colors.
Sea anemones vary in size. Most are from 1 to 5 cm (0.4 to 2 in) in diameter and 1.5 to 10 cm (0.6 to 4 in) in length, but they are inflatable.
Stichodactyla mertensii, commonly known as Mertens’ carpet sea anemone, is a species of sea anemones in the family Stichodactylidae. It is regarded as the largest sea anemone with a diameter of over 1 meter (3.3 feet). At their smallest, sea anemones can be around the size of a pinhead.
Sea anemones are typically predators, ensnaring prey of suitable size that comes within reach of their tentacles and immobilizing it with the aid of their nematocysts.
Although sea anemones can catch fish and other prey items, some species obtain much of their nutrients from symbiotic unicellular algae.
Other symbiotic relationships are formed between sea anemones and various fish or crustaceans. They clean the anemone by eating the algae and other food leftovers on them. Some protect the sea anemones by chasing away polyp-eating fish. Such mutually beneficial symbiotic relationships reflect the harmony of creation.
In addition to their ecological values in the marine environment, sea anemones, with their petal-like, often colorful tentacles, provide aesthetic benefit to humans in terms of their beauty of color and form.
While many prefer to stay fixed in one place, some anemones choose to move from one point to another. Some slowly creep along surfaces using the suction of their feet, as slugs would do on land. Other anemones tumble or somersault. And others, still, simply let go of whatever surface to which they cling and allow themselves to float away or “swim” by gently squirming through the water.
Sea anemones have great powers of regeneration.
Anemones reproduce in a variety of ways. They can reproduce asexually, budding off what are essentially identical twins from a single specimen. This can result in the formation of a large colony of identical individuals such as can be observed in the local intertidal with the aggregating anemone. They can also reproduce sexually by broadcast spawning, where fertilization takes place in the water. The resulting larvae then swim around in the plankton until they find a suitable place to settle, at which time they metamorphose into a young anemone.
With their stinging tentacles, sea anemones seem an unlikely meal choice for most ocean-dwelling creatures. However they are eaten by sea slugs, certain starfishes, eels, flounders, and codfish.
Most sea anemones are harmless to humans, but a few highly toxic species (notably Actinodendron arboreum, Phyllodiscus semoni and Stichodactyla spp.) have caused severe injuries and are potentially lethal.
Sea anemones have become very popular inhabitants for both the reef tank and the saltwater aquarium. Watching an anemone living in a cooperative relationship with a colorful Clownfish is a rewarding experience.
Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Hexacorallia.
Unlike jellyfish, sea anemones do not have a medusa stage in their life cycle.