Soft corals come in shapes that look like whips, plumes, or fans and have only eight tentacles.
Stony corals build a hard skeleton out of calcium carbonate and have tentacles arranged in multiples of six. Zooxanthellae take carbon dioxide and ammonia waste from the coral and in return the coral receives amino acids and oxygen from the plants. They work together in a type of beneficial relationship called mutualism. Zooxanthellae need sunlight to produce food since they are plants. Corals also need warm water with moderate wave action to carry in oxygen and tiny bits of food, high salinity levels, plus low levels of carbon dioxide, nitrogen,and phosphate to survive.