1. Bilaterally symmetrical

2. Segmented

3. Open Circulatory System

4. Exoskeleton

5. Ventral Nerve Cord

6. Dorsal Artery 

Class: Trilobita 

(crabs, shrimp, pill bugs)

1. two pairs of antennae

2. Appendages on most segments (mostly aquatic) 

true insects;

a) 1 pair of antennae

b) 3 major body regions- Head, Thorax, Abdomen

c) 3 pairs of walking legs

d) most have wings 

"inside out";

1. Multilayered external shell that varies dynamically with time and location;

2. Outer layers of integument protects animal from water loss (wax, cement on outside)

3. Exocuticle and Endocutical are composed of microfibers of chitin surrounded by a matrix of protein that becomes rigid when scelrotization occurs. 

a) efficient at small size

b) tubular design is stronger than rod for less weight

c) flexible enough and light enough for flight

d) provides good protection for soft internal structures 

a) growth must occur in discrete steps; expansion to new size occurs immediately after molting

b) size limiting factors and the surface area to volume problem 

sensory, ingestion, houses brain;

1. antennae, compound eyes, mouthparts 

1. locomotion (legs, wings)

2. three segments (pro-,meso-,metathorax), wings on last two 

1. typically jointed, many pairs, maybe as many as one pair per body segment

2. appendages that are modified into antennae, mouthparts, legs (NOT wings) 

labrum, mandibles, maxillae, labium;

1. various modifications of mouthparts illustrate how insects can vary the same basic plan to different, specialized structures

2.examples: grasshopper, sucking bug, mosquito, bee, butterfly