- A taxonomic purchase inside the superorder Peracarida — very many shrimplike crustaceans.
- A numerous group of fourteen -- footed Crustacea, inhabiting both fresh and sodium liquid. The human body is usually squeezed laterally, while the anterior sets or feet are directed downward and ahead, nevertheless posterior legs are usually switched up and backwards. The beach flea is an illustration. See tetradecapoda and arthrostraca.
- In zoology, an order of sessile-eyed (edriophthalmous) crustacean arthropods: occasionally, as by Dana, united with Isopoda in an order Choristopoda.
- small flat-bodied semiterrestrial crustaceans: whale lice; sand-hoppers; skeleton shrimp