Oligostraca
Oligostraca is a superclass of crustaceans. It consists of the following classes:
Class Mystacocarida: Minute crustaceans restricted to interstitial marine sediments. Locomotion depends completely on the presence of dorsal and ventral substrates.
Class Ostracoda : Small planktonic, demersal and benthic crustaceans with a cosmopolitan aquatic distribution in both freshwater and marine environments, and a few in damp terrestrial habitats. Often called seed shrimps because their body is enclosed within a small and bivalved carapace, which makes them look like seed.
Class Ichthyostraca:
Class Skaracarida: Long-bodied, marine, likely benthic detritivores. Only contains the genus Skara. Extinct, fossils known from the Cambrian.