Photo by Scott HeckmanThis coral is non-photosynthetic and does not require much light. Place this coral under an overhang or into a cave out of direct light. Ensure that there is moderately strong flow across this coral.This is a very interesting specimen for the reef aquarium.Polyp extension is best seen after the lights are out and in moonlighting.This coral takes its nutrients from the water column. Marine snow and plankton are recommended.Corals are part of a biological group known as Cnidaria. Most Cnidaria have a mouth,or mouths, that opens into one big body cavity. Due to the lack of a true digestivesystem, this cavity acts in its place and after the food is broken down thenutrients are then sent through the rest of the body as food. There is also noexcretory system; therefore the waste is sent back through the mouth or secretedinto the surrounding water.Tentacles of varying size will usually surround the mouth of Cnidaria. Most Cnidariahave tentacles with stinging cells that can shoot tiny poison darts into their preyor can even be used as a defense mechanism. Some corals lack tentacles and insteadcover themselves with a thin layer of mucus and use that to collect bacteria andplankton as food. Some corals even use both of these methods. Cnidaria can either bean individual animal or members of a complex colony. These "Colony Corals" share thefood and nutrients taken in by each individual.Corals have tiny living organisms that actually live in their tissue. These arecalled zooxanthellae and they are the reason why such strong lighting is needed inthe saltwater aquarium. These algae-like creatures provide the coral with oxygen andother nutrients that are produced during photosynthesis. During this process, thezooxanthellae take up carbon dioxide and provide nutrients to the coral.Corals can use two different types of defense mechanisms. One of which is a sweepertentacle wherein the coral reaches its tentacles out to try to damage another coralwith nematocysts. The other is when the coral releases a minute amount of toxin intothe water to poison another coral within certain proximity.