Key Terms/Ideas
- Symmetry
- Bilateral Symmetry - Only a single imaginary plane can divide the body into two equal halves
- Radial Symmetry - Body parts that repeat around the center of the body. Any number of imaginary planes can be drawn through the center, each dividing the body into equal halves
- Direction
- Dorsal - Top, Upper side
- Ventral - Bottom, Lower side
- Anterior - Front
- Posterior - Back
- Tissues
- Ectoderm - Outermost layer. Develops into sense organs, nerves, and outer layer of skin
- Mesoderm - Middle layer. Develops into muscles, much of circulatory system, reproductive and excretory organ systems
- Endoderm - Innermost germ layer. Develops into the linings of the digestive tract and much of the respiratory system
- Body Cavities
- Coelom (Ucoelomate) - Fluid-filled body cavity lined with the mesoderm
- Pseudocoelom - Body cavity between the endoderm and mesoderm tissue that is partially lined with mesoderm tissue
- Acoelomates - Animal lacking a coelom or body cavity
- Exoskeleton v.s. Endoskeleton
- Exoskeleton - External skeleton, tough external covering that protects and supports the body of many invertebrates
- Endoskeleton - Structural support located inside the body of an animal
- Cephalization - concentration of sense organs and nerve cells at the front of an animal's body