Body Plan of Animals

The animal body underwent five evolutionary changes:
1. Evolution of Tissues
2. Evolution of Bilateral Symmetry
3. Evolution of a Body Cavity
4. The Evolution of Deuterostome Development
5. The Evolution of Segmentation

        1. Grade of organization of cells
            a. Cellular Level
            b. Tissue Level
            c. Organ Level
        2. Body symmetry
                a. Bilateral
                b. Radial or spherical
                c. Asymmetrical
        3. Number of skin cell layers in early development
            a. Primitive simplest animals lack differentiated dermal layers
            b. More advanced forms
            c. Ectoderm (outer skin)
            d. Mesoderm (middle skin)
            e. Endoderm (inner skin)
        4. Presence or Absence of Coelom (internal fluid-filled cavity in the body, See table 2.1)
            a. Acoelomates
            b. Pseudoacolemates
            c. Eucoelomates
            d. Lophophorates
            e. Schizocoels = protostromes (first mouth)
            f. Enterocoels = deuterostomes (second mouth)
        5. Presence or absence of segmentation: Divisions of the body