Animals may be asymmetrical, radial, or bilateral in form (Figure 15.4). Asymmetrical animals are animals with no pattern or symmetry; an example of an asymmetrical animal is a sponge (Figure 15.4 a). An organism with radial symmetry (Figure 15.4 b) has a longitudinal (up-and-down) orientation: Any plane cut along this up–down axis produces roughly mirror-image halves. An example of an organism with radial symmetry is a sea anemone.
Bilateral symmetry is illustrated in Figure 15.4 c using a goat. The goat also has upper and lower sides to it, but they are not symmetrical. A vertical plane cut from front to back separates the animal into roughly mirror-image right and left sides. Animals with bilateral symmetry also have a “head” and “tail” (anterior versus posterior) and a back and underside (dorsal versus ventral).
Watch this video (http://openstaxcollege.org/l/symmetry2) to see a quick sketch of the different types of body symmetry.