| A | B |
|---|
| phylogeny | evolutionary history of a species based on comparative relationships of structures and comparisons of modern life forms with fossils |
| symmetry | the similarity or balance among body structures of organisms |
| radial symmetry | body plan that can be divided along any plane, through a central axis, into roughly equal halves |
| bilateral symmetry | body plan that can be divided into mirror images along only one plane through the central axis |
| anterior | toward the head end of an animal with bilateral symmetry |
| posterior | away from the head end of an animal with bilateral symmetry |
| cephalization | tendency to concentrate sensory organs and nervous tissue at an animal’s anterior end |
| dorsal | backside of an animal with bilateral symmetry |
| ventral | underside or belly of an animal with bilateral symmetry |
| coelom | fluid-filled body cavity completely surrounded by mesoderm |
| pseudocoelom | fluid-filled body cavity between the mesoderm and the endoderm |
| acoelomate | animal with a solid body that lacks a fluid-filled body cavity between the gut and the body wall |
| protostome | coelomate animal whose mouth develops from the opening in the gastrula |
| deuterostome | coelomate animal whose anus develops from the opening in the gastrula |
| plane | an imaginary line that divides a body form into two parts |
