Cladocerans have a single compound eye and often a smaller secondary eye, the ocellus. A carapace covers the body, including the 4 to 6 pairs of thoracic appendages. The carapace is often transparent and opens ventrally and posteriorly. The abdomen and postabdomen are generally bent forward under the thorax. The postabdomen bears two large claws used primarily for cleaning debris out of the carapace.
Swimming is accomplished by downward strokes of the large second antennae.
A few species are predacious but most are herbivores or detritivores, feeding on phytoplankton, attached vegetation or decaying organic material. In most planktonic species complex movements of the thoracic appendages produce a constant current of water between the valves. Small particles in the water are filtered out by fine setae on the thoracic legs and moved along a groove at the base of legs to the mouth. Although there is some evidence that certain types of food, such as particular types of algae, Protozoa, or bacteria may be selected by some species, it is generally believed that all organic particles of suitable size are ingested without any selective mechanism. When undesirable material or large tangled masses are introduced between the mandibles, they are removed by spines on the first legs and then kicked out of the carapace by the postabdomen.