Endoscope view of ostracods moving about on a sandy pond bottom. Ostracods are small crustaceans whose bodies are enclosed within a bivalve-like shell, which is hinged at the top and opened to allow their antennae to protrude. The antennae are used for locomotion. Ostracods are common in freshwater and marine habitats worldwide, usually living on the substrate and feeding on bacteria, algae and detritus.