P3.88 Friday, Jan. 6 Modification of velar lobe morphology across different developmental modes in Calpytraeid gastropods HOFSTEE, J.C.*; COLLIN, R.; Smithsonian Tropical Research Institute email@example.com
Mode of development in marine invertebrates can include planktotrophic larvae, lechithotrophic larvae, direct development from large eggs and direct development with nurse eggs. It is generally believed that evolutionary changes in development are more likely to result in the loss of feeding larvae than in the re-evolution of feeding larvae from direct developers. A transition from planktonic larvae to direct development can lead to the loss of complex feeding structures which are essential in planktonic larvae for particle capture. In gastropods this often includes the reduction in the size of the velum and reduction or loss of the velar cilia (the prototroch, metatroch, and food groove). Direct developing species that lose these feeding structures are thought to be un-likely to re-evolve planktotrophic larvae. Phylogenetic analysis of calyptraeid gastropods, however, suggest that feeding larvae have re-evolved in this group. Therefore we used SEM to examine a variety of developmental stages of 13 calyptraeids including planktotrophs, lecithotrophs and direct developers both with and without nurse eggs, to determine the extent of the reduction of the velum and its ciliation species lacking feeding larvae. We found typical velar lobe ciliation in embryos of planktotrophs as well as embryos with direct development with nurse eggs. This was true for most direct developers as well, although two, Bostrycapulus aculeatus and Crepidula ustulatulina, lacked metatrochal cilia. These results suggest that most species may have the potential to re-evolve planktotrophic larvae but, for the species with lost or modified ciliation, reacquisition of feeding larvae is not likely.