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American Zoologist 1994 34(4):562-569; doi:10.1093/icb/34.4.562
© 1994 by The Society for Integrative and Comparative Biology
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The Nauplius Larva of Crustaceans: Functional Diversity and the Phylotypic Stage1

TERRI A. WILLIAMS2
Department of Biology, Macalester College 1600 Grand Ave., St. Paul, Minnesota 55105

SYNOPSIS. The crustacean nauplius larva is a development stage characterized by the presence of three pairs of head appendages. All crustaceans pass through the naupliar stage whether embryonically or as freeliving larvae. The nauplius is thought to be the phylotypic stage and represent a fundamental developmental constraint in crustaceans. However, free-living nauplii are primitive and I present evidence that this form is functionally plastic, e.g., locomotory modes are diverse even in closely related species. I argue that this functional plasticity allowed the persistence of nauplii in the early evolution of crustaceans and, as a consequence, naupliar development became a deep-seated feature of crustaceans. Thus, we see nauplii as phylotypic. This suggests that, in spite of the presence of phylotypic stages in various phyla, phylotypy itself may not represent a similar, underlying developmental constraint in every case.


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