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 (with one exception) carapace, which makes them look like seed.

Class Ichthyostraca:
:Subclass Branchiura (fish lice): Ectoparasitic crustaceans on marine and freshwater fish, ranging in size from a few millimeters to 30 mm. A carapace is covering most of their body, which is dorsoventrally flattened.