The diverse appearance of animals is mostly superficial; the bewildering variety of known forms, some truly bizarre, can be assorted among a mere half-dozen basic body plans. These plans are established during the embryonic stages of development and limit the size and complexity of the animals. Symmetry, number and relative development of tissue layers, presence and nature of body cavities, and several aspects of early development define these fundamental modes of organization.
In this lesson, we embark on a tour of the animal kingdom that will continue for the rest of this quarter. Here we will consider the characteristics that all animals share, as well as the evolutionary history of this kingdom of consumers.
