Radial Symmetry and Cephalization Evolved Together in the Acoelomate Animals

Question

Radial symmetry and cephalization evolved together in the acoelomate animals.

Accepted Answer

Radial symmetry is characteristic of many simple, sessile, or free-floating animals such as cnidarians (e.g., jellyfish), which do not exhibit cephalization. Cephalization, the development of a head region where sensory organs and nerve cells are concentrated, is associated with bilateral symmetry and is seen in more complex, mobile animals, including many acoelomates like flatworms. These two traits did not evolve together; rather, cephalization is associated with bilateral symmetry, not radial symmetry.