Echinoderm Larvae and Phylogeny

Abstract

New robust phylogenies for echinoderms, based on congruent patterns derived from multiple data sets, provide a sound foundation for plotting the evolution of life-history strategies and comparing rates and patterns of larval and adult morphological change. This approach demonstrates that larval morphology has been evolving independently of adult morphology, that larval morphology displays more homoplasy than adult morphology, and that early developmental patterns are remarkably flexible. Larval morphology on its own can mislead phylogenetic analysis, not because of lateral gene transfer among distantly related taxa, but because of massive convergence in the form of nonfeeding larvae brought about by the loss of complex structures and the strong functional constraints on feeding larvae. The degree to which larval tissue is resorbed at metamorphosis is believed to be important in determining adult body plan. Although the correspondence is not precise, it does provide a model for understanding skeletal homologies among the classes.