Nauplii are primary larvae of many crustacean groups, and are characterized by having three pairs of limbs and a single eye. They lead an independent life which is often very different from that of the adult. The morphology, development, movement and feeding of Nauplius larvae are shown using examples from various systematic groups. As a comparison, the marine water flea, with its direct development, and the Zoea and Megalopa, as the larval stages of a crab, are shown. Slow-motion sequences.