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The shape and function of animals differ. Every organism, from a sponge to a worm to a goat,
has a unique body plan that restricts its size and shape. Whether they live in the deep sea, a rainforest
canopy, or the desert, animals' bodies are made to interact with their environments. As a result,
studying an organism's environment can teach us a lot about the anatomy and physiology of that
organism's body as well as how its cells, tissues, and organs work.
Body Plans
Animal body plans follow set patterns related to symmetry. They are asymmetrical, radial, or
bilateral in form as illustrated in Figure 123.
Asymmetrical
animals are animals with no pattern or
symmetry; an example of an asymmetrical animal is a sponge. When an animal is up-and-down
oriented, as shown in Figure 123, a plane cut through the organism along its longitudinal axis will
result in equal halves, but not a clear right or left side. This strategy is primarily used by aquatic
animals, particularly by organisms that attach themselves to a base (such as a rock or a boat) and draw
their food from the water that flows around them. In the same drawing, a goat serves as an example
of bilateral symmetry. The goat also has an upper and lower portion, but a plane cut from front to
back clearly distinguishes the right and left sides of the animal. The terms anterior (toward the front),
posterior (toward the back), dorsal (toward the back), and ventral are also used to describe positions
in the body (toward the stomach). Animals with bilateral symmetry are able to move very quickly
and are found in both aquatic and terrestrial environments.
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