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The penaeids are unique amongst the decapods in having a free- swimming naupliar stage. The nauplius is pyriform, larger at the anterior end, with three pairs of natatory cephalic appendages: a pair of antennules, a pair of antennae and mandibles. Swimming, with oarlike sweeps of the cephalic appendages, is intermittent with almost equal amounts of time spent motionless, during which the nauplii slowly sink. There is a median naupliar eye. The number of substages reported varies from three to eight. In the early substages the appendages and the body region behind the mandibles are unsegmented. With subsequent moults the appendages become annulated or segmented, a rudimentary carapace appears, the body elongates and rudiments of new body segments and appendage buds of the two maxillae and first two maxillipeds appear. The posterior margin becomes bilobed and the number of caudal spines increases. The mandibles develop swelled masticatory surfaces (gnathobases), but the gut is incomplete and the nonfeeding larva lives on yolk reserves until the protozoeal stage (Dall et al, 1990). |
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