The large branchiopods are an ancient group of crustaceans which most likely originated in marine waters. Long ago, most probably due to predatory bone fish in the Devonian, they were forced to make their home in the chemically more variable inland waters of the world. Usually they can be found in ephemeral pools or saline lakes. Anostracans, fairy and brine shrimps, differ from other large branchiopods in having stalked compound eyes and in not having any shield covering the body. Their external morphology has not changed since the Jurassic.
Fairy shrimps are backstrokers, their ventral side is oriented to the light.
Setae of the ventral groove transport the nutritive pulp to the mouth. Adult females have an ovisac where the mature eggs are continuously moved to be supplied with oxygene. Adult males show prominent antennar appendages used for clasping the females during pairing. Tadpole shrimps usually live near the ground of astatic pools, where they move with their ventral side down. Notostracans sometimes even cannibalize freshly moulted members of the same species.