Nauplius larvae are the larval stages of some crustaceans (such as copepods and barnacles) and this larval stage distinguishes crustaceans from other arthropods. They have three pairs of jointed appendages and usually a single compound eye, known as a naupliar eye. The larval stage is numbered according to how many molts or stages the larva has passed through (eg. nauplius I and nauplius II).