Animal body plans can be classified as having no symmetry, radial symmetry, or bilateral symmetry.
Bilateral symmetry is the most common animal body plan.
Animal body plan is closely related to lifestyle and habitat. All animals with radial symmetry live in water. One division of the animal phyla into two separate lineages depends on cell events occurring very early in embryonic development. In protostomes, the earliest cells of the embryo move in a spiral pattern and the divisions are determinate. The first opening in the embryo becomes the mouth.