Actinaria

What are they?

Sea anemones are soft bodied animals, classified under the group Actinaria. Actinarians usually have column shaped bodies - with a mouth at one end, and a pedal disk at the other end. The mouth is situated on the oral disk - a ringed row of tentacles. They can reproduce sexually, or asexually.

How do they live?

The anemones are found on the rocky stones and coral reefs around the world. Some can be found at a low depth. Most live a stationary life for the most part - they are attached to rocks or other substrates - and do not move, or do so slowly, by contraction of the disk. Some burrow into the sand, other move by bending the bodies or flapping their tentacles. There are more than 900 species of such animals. They sometimes move like the hydra.

They have soft bodies, and cover themselves with a mucus like secretion. They may also use a coating of sand grains, but there are not many fossils.

These animals lack a medusa stage, they live as polyps. Some may retain their stinging cells, though, for a healthy diet , other make their balanced diet by growing some symbiotic algae on themselves. Reef building algae, owe their success to the algae living in them ( the dinoglagellate algae ). They live in their tissue. Coral use their tentacles to feed, though the algae may produce most of it's food. That's why coral building polyps live near the surface ( the algae can't live without sunlight ). The other polyps ( ones without algae in them ) go to the inner realms of the water.

You might want to read more on Coral.