Meeting Abstract

70.4  Sunday, Jan. 6  Larval Development of a Neritimorph Gastropod Identifies Derived Traits Among Feeding Gastropod Larvae PAGE, L.R.*; LESOWAY, M.P.; University of Victoria lpage@uvic.ca

Mapping of gastropod life histories onto recent phylogenetic hypotheses predicts that larval feeding (planktotrophy) is a derived trait among gastropods. Feeding larvae are present in three clades: caenogastropods, heterobranchs, and neritimorphs. To date, detailed information on larval growth and morphogenesis is available only for caenogastropods and heterobranchs, which are sister groups. The Neritimorpha is the most basal clade among these three, yet minimal information on larval neritimorphs makes it difficult to predict polarity of evolutionary change for characters of planktotrophic gastropod larvae. Our study on Nerita atramentosa from Sydney Harbour, Australia revealed some unusual patterns of growth and development relative to other feeding gastropod larvae. The larval shells of N. atramentosa arrested growth during delay of metamorphosis, but the radula continued to elongate. This pattern is more similar to that described for non-feeding larvae of vetigastropods, than to patterns described for feeding larvae of either heterobranchs or caenogastropods. Furthermore, our results suggest that continued larval shell growth during delayed metamorphosis, which occurs in some species of caenogastropods, is a derived feature among planktotrophic gastropod larvae. Large larval size and continued growth following onset of metamorphic competence correlates with evolution of predatory feeding habits within the post-metamorphic stage of some caenogastropods, where a complex adult foregut and incipient proboscis achieve advanced differentiation in the larva prior to metamorphosis. We hypothesize that differences in growth potential of gastropod larval shells, and thus size of soft tissue mass, facilitated the evolutionary emergence of predatory feeding among post-metamorphic gastropods.