Actiniaria (Anemones)

There are about 1,350 known species of anemones. They are found from deep to shallow waters, attached to hard surfaces or burrowing into the ground.

Most anemones are small, from 1.5-10cm long and 1-5cm in diameter. But some can be 50cm in diameter or more! Unlike hard corals which are colonies of small polyps connected to one another that produce a hard skeleton, anemones are larger solitary polyps that don’t produce a hard skeleton. Like jellyfish and other cnidarians, anemones have tentacles with stingers. The upper side of the oral disk is usually covered with lots of tentacles. The tentacles are armed with stingers that are used for feeding and self-defense.

Most anemones don’t move around a lot. Anemones also have a long smooth body column. ending in a flat muscular pedal disk that attaches to a hard surface. Some anemones can move slowly by gliding on the pedal disk.

In most anemones, the body column can retract towards the base to hide from predators or minimise exposure at low tide. Most can also tuck their tentacles and oral disk into the body column.

Anemones may use their tentacles or mucus to trap small particles, detritus and plankton from the water. Larger anemones can capture and swallow prey such as fish whole.

Many anemones like coral polyps also harbour symbiotic single-celled algae (called zooxanthellae) in their tentacles. The algae undergo photosynthesis to produce food from sunlight, which is shared with the anemone.

Source: Wikipedia