Subclass Ostracoda is a class of small crustaceans commonly known as seed shrimps. Some synonyms for the subclass include the ostracods, ostracodes or ostracopods. Other terms might include bivalved crustaceans, cyprids, and podocopids. Ostracods are found in a wide variety of aquatic habitats, from freshwater to marine environments, and they play important roles in many ecosystems as both predators and prey. The subclass is characterized by their two-valved carapace, or shell, and a pair of antennae used for locomotion and feeding. The ostracods are an ancient lineage of crustaceans with a rich fossil record that dates back over 500 million years.