The phase of larval development characterized by 2 pairs of functional appendages (the 1st and 2nd antennae). The mandibles are reduced and no longer serve as swimming appendages. Buds of the 1st and 2nd maxillae and maxillipeds are present. A carapace covers the anterior portion of the body, and an unsegmented abdomen bears posterior spines. In species which shed their eggs freely into the water there is one metanauplius stage. In species which brood their eggs there is a newly-hatched form, the pseudometanauplius, and the metanauplius form. These forms may be separated by the molt of a thin cuticle soon after hatching (Lebour 1924) or the pseudometanauplius may develop into the metanauplius without molting (Komaki 1967).