Answer:
Corals belong to the phylum Cnidaria and class Anthozoa. They are marine invertebrates. They live in colonies and excrete calcium carbonate which forms a hard exoskeleton. Thus over many generations, the colony creates a large exoskeleton.
Each coral group is a colony of identical polyps. A polyp is a cylindrical animal with sac like structure. It is around few centimeters in length and few millimeters in diameter. The mouth opening is surrounded by a set of tentacles. It obtains nutrition by eating photosynthetic unicellular dinoflagellates. Sometimes it can also catch small fish and plankton by using stinging cells present on tentacles. It can produce both asexually and sexually.