What exactly is a coral reef?
These beautiful marine invertebrates are among the most primitive of multicellular animals and possess a simple nerve network and digestive system. They belong to a group of animals, the coelenterates, which includes sea firs, jellyfish, sea fans, soft corals, anemones, and true corals. Unlike jellyfish, corals and their nearest relatives have developed the polyp stage to the exclusion of a free-swimming stage, spending most of their life permanently fixed to the seafloor. The sea anemones consist of solitary polyps and , although devoid of a calcareous or horny skeleton, may reach up to two feet in diameter. Sea pens and sea fans have a horny skeleton, which gives them a passing resemblance to true coral, however, the skeleton of coral is calcareous rather than horny. The calcareous coral skeleton consists of calcium carbonate crystals which are extracted from the sea and laid down by the epithelial cells of the base and lower body wall of the coral animal, which is known as a polyp.
