11. Enterocoelous development is the stage of embryological development of deuterostomes in which the coelom forms. 12. The coelom of the body forms from a split of the mesoderm along the somite axis. 13. The second circulatory system derives from the cells of the digestive system that line the coelom . 14. Pedicles of inarticulate species are extensions of the main coelom , which houses the internal organs. 15. This is the part extending from the protocele, ie the uppermost portion of the coelom . 16. Haemal and perihaemal systems are derived from the coelom and form an open and reduced circulatory system. 17. Some of the body cavities degenerate but others become the water vascular system and the visceral coelom . 18. The muscular layers are longitudinal and circular, and part of the fluid-filled coelom within. 19. Some of the ( lesser known ) animals with true coeloms shared both deuterstome and protostome traits. 20. In bilaterally symmetrical organisms there is often a major mesentery separating the two halves of the coelom .
