Nauplius, the name of one of the principal of larval forms of Crustacea. Unlike the adults, the body of the larva is not divided into a series of divisions or segments; it has, moreover, only three pairs of appendages, which correspond to the two pairs of feelers or antennae and the mandibles or jaws. Another difference from the adult is the possession of only a single eye in the middle line of the head instead of a pair placed one on either side. The name was given to this larva under the impression that it was a distinct animal, before its life-history was discovered. This form of larva is typical of the subdivision of the Crustacea known as the Entomostraca (q.v.); it occurs, however, in two members of the other group - the Malacostraca (q.v.), viz. the genera Euphausia and Pentcus, while in a third genus, Lucifer, there is an allied form known as the Meta-Nauplius, which differs from the nauplius by the presence of two additional pairs of limbs.