It is not the hard coral skeleton that provides nourishment, but the soft bodied structures coral polyps that grow on the surface of the skeleton. The polyps look like miniature sea anemones, except that most live connected together in colonies contain ing hundreds of individuals. Living in coral polyp cells are single-celled algae known as zooxanthellae. Any coral skeletal material that is swallowed is crushed by the grinding action of special teet h found in the parrotfish's throat called the pharyngeal mill. This makes its way through the fish's digestive system and is deposited on the reef as white coral sand.
Some fish return to the same spot to release their waste products which form small hills of sand.
It has been estimated that parrotfish produce as much as one ton of coral sand per acre of reef each year. Classification and Characteristics Early scientists identified over 350 different kinds of parrotfish, but it is now known that there are only 80 members of Family Scaridae. The early confusion came about because these fish have a number of color phases which look quite different. There is still some disagreement, but among Atlantic species most people recognize two major genera, Scarus and Sparisoma. Sparisoma is restricted to the Caribbean, while Scarus is found in all tropical seas and even the Mediterranean Sea.