An animal that has body parts that extend outward from its center show radial symmetry. The body plans of echinoderms, ctenophores, cnidarians, and many sponges and sea anemones show radial symmetry. A coelom is a body cavity completely lined with mesoderm. The coelom exists in multicellular organisms.It is a fluid-filled body cavity that is completely lined by tissue created from the mesoderm.