Water flea (Cyclops sp.) nauplius larva, light microscopy. This freshwater crustacean has a single large simple eye, which led to it being named after the Greek mythical creature Cyclops. A nauplius is the first larval stage of a crustacean in which the thorax and abdomen have not developed yet. Nauplii larvae do not feed, but use internal yolk reserves from the egg for energy.