Nauplius(redirected from Nauplios)
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the plankton larva of numerous species of the family Crustacea. The body is unsegmented and has three pairs of appendages. In front of the mouth there are uniramous sensory antennules; in back there are biramous antennae and mandibles for swimming. The nauplius has a median eye. Between the mandibles and the anal opening there is a growth zone, where, as development progresses, the postnauplial segments with appendages develop.