Daphnia, commonly known as water fleas, are small, freshwater crustaceans belonging to the order Cladocera. They typically measure between 0.2 to 5 millimeters in length and are characterized by their transparent bodies and large, prominent eyes. Daphnia play a crucial role in aquatic ecosystems, serving as a food source for various fish and other aquatic animals. These organisms reproduce both sexually and asexually, depending on environmental conditions. In favorable conditions, they can produce eggs that develop into new individuals without fertilization, a process known as parthenogenesis. Daphnia are also used in scientific research, particularly in studies related to ecology and toxicology.