The Order Cladocera comprises small, mostly freshwater crustaceans commonly known as water fleas. They are an important component of aquatic ecosystems, serving as primary consumers that feed on algae, bacteria, and detritus, and in turn, provide a vital food source for fish and other predators. Cladocerans are characterized by a bivalve-like carapace, a pair of large antennae used for swimming, and simple, often transparent bodies. Many species reproduce by cyclical parthenogenesis, alternating between asexual and sexual reproduction depending on environmental conditions. Their rapid reproduction and sensitivity to water quality make them important indicators in ecological studies and freshwater monitoring.