Arthropods are a large group of animals distinguished by having a chitinous, segmented exoskeleton (outer skeleton) and jointed appendages. Examples of arthropods found in the Pacific Northwest include:

1. Insects: Characterized by 3 pairs of jointed legs and body divided into 3 major segments. Frequently one may see one pair of antennae on the head and many possess wings. Insects are terrestrial and aerial. Only a handful may be found living by choice in marine habitats.

2. Arachnids: Characterized by 4 pairs of jointed legs and body divided into 2 major sebments. Antennae are lacking from the head and none possess wings.

3. Crustaceans: Characterized by 5 pairs of large jointed legs (one pair may be pincers) or in some cases one pair of legs per body segment. The body is frequently divided into 2 major areas, with the tail divided further into smaller segments. Crustaceans have 2 pairs of antennae. They are largely aquatic, although some are terrestrial. None have wings.

4. Centipedes: Characterized by a small head with similar shaped body segments. One pair of jointed legs is found per body segment. One pair of antennae are found on the head.

5. Millipedes: Characterized by a small head with similar shaped body segments. Two (occasionally one) pair of jointed legs is found per body segment. One pair of antennae are found on the head.