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a family of crustaceans of the subclass Copepoda. The animals measure 1–5.5 mm in length. They have a single median eye (hence the name). The antennules are short, and the antennas are single-branched and are used for swimming. The abdomen is longer than the cephalothorax. The females have two egg sacs. The heart is absent. The family includes approximately 250 species distributed throughout the world.
Cyclopidae live mostly in freshwater. Benthopelagic or, sometimes, pelagic organisms, the animals are predators that feed on protozoans, rotifers, and small crustaceans. In turn, Cyclopidae serve as food for fish and fry. They are intermediate hosts for parasitic worms, such as the guinea worm and the broad tapeworm.