Slide 54:

The tiny seed shrimp, or ostracods, seem to have the same ideas the clam shrimp. Their bodies are completely surrounded by a pair of shells hinged at the back. The shells gape to allow the appendages to protrude while swimming, or scooting along the bottom. Seed shrimp live by straining bacteria, algae, and other small food particles from water, which is circulated between the shells. Ostracods are usually less than one millimeter long.