sea anemone - Anatomy, Life cycle, Ecology, Gallery

A typically solitary, marine coelenterate with a cylindrical body attached at its base to a substrate, and bearing a circle of tentacles at the top around its mouth; some species form colonies; c.800 species known, from the inter-tidal zone to abyssal depths. (Phylum: Cnidaria. Order: Actiniaria.)

iSea anemone
Sea anemone at the Monterey Bay Aquarium
Scientific classification
Kingdom: Animalia Phylum: Cnidaria Class: Anthozoa Subclass: Hexacorallia Order: Actiniaria
Diversity
46 families
Suborders
Endocoelantheae Nyantheae Protantheae Ptychodacteae

Named after a terrestrial flower, the anemone, sea anemones form a group of water dwelling, filter feeding animals of the order Actinaria. Other close relatives of the sea anemone are the solitary, tube-dwelling anemones and the hydras.

Anatomy

A sea anemone is basically the typical polyp: a small sac, attached to the bottom by an adhesive foot, with a column shaped body ending in an oral disc.

The internal anatomy of anemones is very simple.

The muscles and nerves in anemones are much simpler than those of other animals.

Life cycle

Unlike other cnidarians, anemones (and other anthozoans) entirely lack the free-swimming medusa stage of the life cycle: the polyp produces eggs and sperm, and the fertilized egg develops into a planula that develops directly into another polyp.

A few anemones are parasitic to marine organisms.

The sexes in sea anemones are separate.

Ecology

The sea anemone has a foot which in most species attaches itself to rocks or anchors in the sand. Although not plants and therefore incapable of photosynthesis themselves, many sea anemones form an important symbiosis with certain single-celled green algae species which reside in the animals' gastrodermal cells.

Some sea anemones form symbiotic relationships with crabs, shrimp or with anemone fish, also known as clownfish. In the former situation, anemones will either attach or be attached to the shell of a hermit crab (by the crab's own volition), providing additional protection for the crab and allowing the anemone to eat scraps when the crab feeds. The clownfish benefits from this symbiotic relationship because it is protected by the anemone and in turn the anemone benefits because it gets food scraps from the clownfish.

Gallery

Sea anemones	A closed sea anemone	Deep–sea anemone	Hundreds of young sea anemones at low tide
Sea anemones in a "mini-reef" marine aquarium	Venus flytrap sea anemone