The general structure of an animal, the arrangement of its organ systems, and the integrated functioning of its parts are referred to as its body plan. As Chapter 19 described, the regulatory and signaling genes that govern the development of body symmetry, body cavities, segmentation, and appendages are widely shared among the different animal groups. Thus we might expect animals to share body plans.
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Bilateral symmetry is strongly associated with cephalization.
The body plans of triploblastic animals can be divided into three types based on the presence and structure of an internal body cavity.
Segmentation facilitates specialization of different body regions.
Appendages that project from the body greatly enhance an animal’s ability to move around.
Nervous systems are important for sensing the environment, processing information, and coordinating movement.
Although animal body plans vary tremendously, they can be seen as variations on five key features:
The symmetry of the body
The structure of the body cavity
The segmentation of the body
External appendages that are used for sensing, chewing, locomotion, mating, and other functions
The development of the nervous system
Each of these features affects how an animal moves and interacts with its environment.