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The nauplius larva of a prawn

A nauplius (plural nauplii) is the first larval stage of animals classified as crustaceans (subphylum of Arthropoda). It consists of a head and a telson. The thorax and abdomen, characteristic of adult crustaceans, have not yet developed.

A prominent characteristic of nauplii is that they have only a single (not faceted) eye (naupliar eye). This eye, located on top of the head, may have a lens and senses the direction of light but does not see images. In later stages, two compound eyes with more visual ability develop at the sides, but the initial eye may also remain, becoming the "third eye" of the creature. Nauplii may prefer to swim towards the light.

Nauplii have three pairs of cephalic appendages with which they swim; in the adult these become the antennules, the antennae, and the mandibles. The name nauplii properly refers to crustacean larvae that use appendages that stem from the head (antennules and antennae) as their main means of swimming.

The naupliar stage is the defining link among crustaceans, as they all pass through this larval stage. Some are nauplii as part of their embryonic development (as is the case for the American lobster), or as the first swimming larvae that hatch out of the egg (as is the case for most common shrimp). Nauplii larvae do not feed, but utilize their internal yolk reserves from the egg for energy. Nauplii of marine crustaceans are important components of zooplankton, providing food for many marine organisms.

[edit] See also

Other developmental stages of crustaceans are:

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