Is coral a plant or an animal?

Both. Coral is made up of two living organisms, an animal and a plant that lives inside of the animal. The animal portion is a simple creature called a polyp, a miniature sea anemone that looks a little like a flower. Single cells of algae live inside the cells of the polyp. The polyp needs the algae to provide energy and recycle nutrients. Like most animals, coral has a skeleton, but unlike mammals and fish, its skeleton is formed by the outer skin and is external to the polyp. This “exoskeleton” is made up of limestone, a hard, white chalky material that acts as the animal’s protective covering and gives coral its unique shape. The polyps build massive, intricate structures called coral reefs, which can be found in warm waters of more than 100 countries.