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the larval stage of crustaceans that follows the nauplius. Crayfish in the metanauplius stage have their first three pairs of appendages, which perform the function of loco-motion. These appendages are converted into antennules and antennae, which perform a tactile function, and into mandibles, which serve to grind food. The metanauplius moves by means of new appendages. In Ostracoda a rudimentary shell appears in the metanauplius stage.