The phylum Cnidaria includes anemones, corals, jellyfish, and hydras. There is only one opening into this cavity, the mouth, through which everything passes in and out. Anthozoa, along with hard and soft corals, are benthic , which means they are attached to rocks or the sea floor.
Most anemones survive in a symbiotic relation with with a marine algae called zooxanthellae .
The zooxanthellae are photosynthetic organisms whose waste products are used by the anemone for food. Since the zooxanthellae require light to carry on photosynthesis, anemones in turn require bright light to thrive in the aquarium. The zooxanthellae are generally a light brown color, the same color as the light brown leather corals that also harbor zooxanthellae. The loss of zooxanthellae, apparent by a whitening of the anemone, usually means the anemone will slowly grow smaller and smaller until it dies. Both of these authors believe that carpet anemones should not be removed from the oceans for the aquarium trade.