A. Body Symmetry

1. Radial symmetry: body can be cut in any plane to produce mirror images. Examples: jellyfish, starfish.

2. Bilateral symmetry: body can only be cut in one plane to produce mirror images. Usually allows for a more motile lifestyle. Examples: earthworms, insects.

B. Cell layers and Organization

1. Endoderm: inner cell layer

2. Mesoderm: middle cell layer

3. Ectoderm: outer cell layer

4. Tissue: group of cells with a common function

5. Organ: group of tissues with a common function

6. Organ system: group of organs with a common function

C. Directional Terms

1. Anterior: toward the head

2. Posterior: toward the tail

3. Ventral: toward the stomach

4. Dorsal: toward the back

D. Body Cavities

1. Coelom: true body cavity surrounded by mesoderm.

2. Acoelomate: animal with no true body cavity. Example: flatworms.

3. Pseudocoelomate: animal with a false body cavity. Example: round worms.

4. Coelomate: animal with a true body cavity. Example: segmented worms.

E. Support Structures

1. Spicules: support structures of sponges that do not aid in movement.

2. Hydrostatic pressure: muscles contract against water pressure in the body.

3. Segmentation: division of body into repeating units (metameres). Allows for specialization of body parts.

4. Exoskeleton: outer support structures of insects. Muscles attach to the inside of the skeleton.

5. Endoskeleton: inner support structures of chordates and some invertebrates. Muscles attach to the outside of bones.

6. Appendages: structures that are attached to the skeleton.

F. Body Temperature Regulation

1. Ectotherms: rely on external factors to maintain body temperature. Use behavior to change body temperature (lying in the sun or shade). Example: reptiles and amphibia.

2. Endotherms: rely on internal mechanisms to maintain body temperature. Example: birds and mammals.

G. Body Coverings

1. Skin: outer covering made of waterproof protein (keratin).

2. Scales: cornified skin cells used to prevent dehydration.

3. Feathers: keratinized appendages of the skin that make flight possible.

4. Hair: cornified appendages of skin that aid in maintaining body temperature.

H. Digestive Tracts

1. Gastrovascular cavity: food enters and leaves through the same opening.

2. Tube-within-a-tube: one way digestive tract with two openings.

I. Nervous Systems

1. Nerve net: nervous tissue equally distributed all over the body for an all-or-nothing response.

2. Cephalization: concentration of the nervous tissue in the head region

J. Reproduction

1. Internal fertilization: male generally places sperm inside female to allow fertilization of the egg inside the body, away from predators.

2. Amniote egg: a waterproof covering with a food and water supply for the embryo.

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