Nauplius \Nau"pli*us\, n.; pl. {Nauplii}. [L., a kind of shellfish, fr. Gr. nay^s ship + ? to sail.] (Zool.) A crustacean larva having three pairs of locomotive organs (corresponding to the antennules, antennae, and mandibles), a median eye, and little or no segmentation of the body. [1913 Webster]