Cladocerans Cladocerans, or water fleas, are small (0.2-6 mm) aquatic crustaceans forming one of the orders of the Branchiopoda. Most inhabit quiet fresh waters. Along with the rotifers and copepods they account for most of the freshwater zooplankton yet most of them are benthic. Most cladocerans are filter feeders that consume phytoplankton which they remove from the water using their setose thoracic appendages. A few are carnivores preying on other cladocerans. In most the body is almost entirely enclosed in a large bivalved caparace from which the head extends anteriorly. The body is laterally compressed. The enlarged second antennae serve as locomotory