any of the crustaceans of the order Anostraca, so called because of their graceful movements and pastel colours. Some grow to 2.5 cm (about 1 inch) or more in length. They occur in freshwater ponds of Europe, Central Asia, western North America, the drier regions of Africa, and Australia. The most common species in Europe is Chirocephalus diaphanus; in North America the most common is Eubranchipus vernalis.