The Biological Bulletin, Vol 182, Issue 2 177-187, Copyright © 1992 by Marine Biological Laboratory

DEVELOPMENT AND REPRODUCTION

Morphology and Development of a Unique Type of Pelagic Larva in the Starfish Pteraster tesselatus (Echinodermata: Asteroidea)

L. R. McEdward
Department of Zoology, University of Florida, Gainesville, Florida 32611

Several unusual features characterize the morphology of the pelagic larva of the starfish Pteraster tesselatus and its metamorphosis into the juvenile stage: (1) morphogenesis of the supradorsal membrane during metamorphosis by fusion of 15 lobes on the aboral region of the body; (2) absence of brachiolar arms and attachment disk; (3) heterochronic acceleration of development in the water vascular system, and use of podia for attachment to the substratum at settlement; (4) radial (rather than bilateral) symmetry of the larva; and (5) congruent larval and adult axes of symmetry, and a transverse orientation of the adult rudiment within the larva. Collectively, these features demonstrate that P. tesselatus has a highly derived mode of development and a larva that is unique among the asteroid echinoderms. In contrast to the current interpretation of this larva as a modified pelagic brachiolaria, I suggest that the unusual larva of Pteraster represents an example of an apparently rare evolutionary transition in animal development: the re-evolution of pelagic larval development from benthic brooding.

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