 They have only four pairs of legs, compared to five or six pairs in Ctenopoda and Anomopoda.Unusually among branchiopod crustaceans, Onychopoda share with Haplopoda the presence of segmented appendages, which are used for grasping prey.Most species of Onychopoda live in the waters of the Ponto-Caspian basin (Caspian Sea, Aral Sea, Black Sea including Sea of Azov), in remnants of the ancient Paratethys ocean.