The phylum coelenterate (or cnidarian), as the image above shows, (hollow body) is a group of animals with a very simple body structure. Their body only contains a mouth, a saclike structure, and tentacles.
There
are two basic
forms of coelenterates: the medusa, or 
swimming
form (jelly fish) and the stationary polyp (the anemone at the right). The difference
between the polyp and the medusa is that the polyp is attached by its pedal
disk to the rocky bottom with its tentacles facing up, and the medusa floats
freely in the ocean with its tentacles hanging down.
The coelenterate mouth (oral disk) is surrounded by a ring of tentacles that contain cells that have small whiplike structures known as nematocysts. These nematocysts are released when the coelenterate senses food or danger. The Portuguese Man-of-War is particularly dangerous to humans.
When potential prey swims into the tentacles, the nematocyst is released. These stinging structures sometimes contain a venom which can paralyse the prey, or the tentacles can simply wrap around the unlucky visitor. When the prey is subdued, it is manuevered to the coelenterate's mouth. Undigested parts are spit back out.
Both polyps and medusa are passive feeders. They do not actively hunt for food. They wait for prey to wander or float into their deadly tentacles.
Anemone colors
and patterns serve chiefly for camouflage in order to 
capture
prey rather than to hide from predators. Their only real predators are sea slugs
and certain snails. An interesting fact is that some nudibranches
(photo on the left) swallow the anemone and their nematocysts work their way
through the slugs' tissue and are used by them as a secondary defense (Cool,
huh!). Click on the photograph of the nudibranch to see its nematocysts up close.
Another interesting fact has to do with the symbiotic relationship that anemones have with certain reef fish. Some fish get food from the tentacles of the anemone, and the fish simply cleans the anemone.
Anemones reproduce by simple division, budding and by releasing eggs and sperm into the water. The aggregating anemone of the California coast is the one anemone that uses simple division to as a regular means of reproduction. It is usually the anemones on the outer edge that reproduce in this manner. It usually takes two days for an anemone to complete this process. Budding (sometimes called brooding) is seen in many types. It is easy to observe when an anemone is attached to an aquarium wall.
Sometimes an anemone can simply be a beautiful thing to see. Click on the word "anemone" below to link to a wonderful underwater photograph of an anemone in its full glory.