develops from coelemic cavity lumen The cavity within the body of all animals higher than the coelenterates and certain primitive worms, formed by the splitting of the embryonic mesoderm into two layers. In mammals it forms the peritoneal, pleural, and pericardial cavities. body cavity celom coelom coelome coelomic cavity coelomic cavity lumen hemocoel space of body compartment ventral body cavity anatomical cavity body cavity precursor body cavity or lining