1. 2.
6
Single-celled animal ancestor
Using the figure as your guide, put each item listed below in the order in which animals
developed body plan traits-from the single-celled animal ancestor to the chordates.
1. Radial symmetry
B. As adults, radial symmetry and no cephalization
C. Mouth-first development
D. Multicellularity
E. Initial segmentation
F. Chordate segmentation
G. Tissues: 2 germ layers
H. Backbone development
1. Anus first development
J. Organs: 3 germ layers; bilateral symmetry; cephalization
3
106 Chapter 9 Animal Evolution, Diversity, and Behavior
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