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).
Subclass Cirripedia (Barnacles)
Barnacles start out as a shield-shaped nauplius. This stage is followed by the settling stage known as a cyprid, the cyprid of gooseneck and acorn barnacles being very similar forms. The cyprid is considered planktonic until it has settled into the substrate. Once the cyprid finds a suitable spot in the intertidal to settle it attaches itself into the substrate and begins its life as a sessile (non-motile) organism. Barnacle molts are also found in plankton samples and can be quite common, especially anywhere where adult barnacles are present in large quantities.