Coelomata

n. body cavity of an embryo

By the broadest definition, a body cavity is any fluid filled space in a multicellular organism. However, the term usually refers to the space, located between an animal’s outer covering (epidermis) and the outer lining of the gut cavity, where internal organs develop. "The body cavity" of human body cavities normally refers to the ventral body cavity, because it is by far the largest one in area.
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(Cnidaria): A phylum in the Animal Kingdom. They are invertebrate aquatic animals showing radial or biradial symmetry. Examples are corals, sea anemones, jelly fish.