Body Cavity and Coelom - Metazoa
Vacuoles, spaces, lacunae and cavities have been of importance in all organisms, may it a be plant or animal. All animals have cavities. The cavities perform different functions in different animals. But most of these are not usually considered body cavities. Spongocoel for example, a cavity in sponges, is really a system of water canals.
Generally by the term body cavity we mean a large fluid filled spike lying between the body wall and the internal organs. Bilateral animals are classified according to the presence or absence of body cavities. There are two types of body cavities in animals the pseudocoelom and the coelom.