Entitled: "Nauplius - Youth form of six Crab fish.", plate X from "The History of Creation" by Ernst Heinrich Philipp August Haeckel, 1884. The genus name Nauplius was published posthumously by Otto Friedrich M羹ller in 1785 for animals now known to be the larvae of copepods. The nauplius stage (plural: nauplii) is characterized by the use of the appendages of the head (the antennae) for swimming. The nauplius is also the stage at which a simple, unpaired eye first appears. The eye is known for that reason as the naupliar eye, and is often absent in later developmental stages, although it is retained into the adult form in some groups, such as the Notostraca.