An order of Entomostraca, including many minute Crustacea, both fresh-water and marine.

A subclass of crustaceans with about 4,500 species, including several specialized parasitic orders. The free-living species are small (one to several mm.) and have cylindrical bodies, one median eye, and two long antennae. One order is planktonic (Calanoida), one is benthic (Harpacticoida), and one has both planktonic and benthic species (Cyclopoida). In most species, the head appendages form a complex apparatus used to sweep in and possibly filter prey (especially algae). Thoracic appendages are used for swimming or crawling on the bottom. One of the most abundant group of animals on earth, they are a major link in aquatic food webs.

minute planktonic or parasitic crustaceans