Slide 48:

The rest of our arthropods have a pair of mandibles instead of chelicerae. These can be worked together to grasp, or chew food and move it into the mouth. The two major groups of mandibulates are crustaceans, and the insects.

Fairy shrimp are fairly common crustaceans which appear in ponds and sloughs in early spring. They can be seen gliding slowly on their backs, propelled by fanning motions of leaf-like appendages, or darting like minnows. Fairy shrimp disappear in June as the water becomes warm.