Collin, R.*; Chaparro, O. R.: Loss of Feeding Larvae in Crepidula (Gastropoda: Calyptraeidae) is Not Irreversible

It is thought that species of marine invertebrates with planktotrophic development commonly give rise to species with direct development. Direct developers often lose the complex morphological characters necessary for planktotrophic development and therefore cannot give rise to species with planktotrophic larvae. Here we show that, contrary to expectation, planktotrophic development in Crepidula fecunda appears to be derived from a direct developing ancestor, C. dilatata. Phylogenetic analysis of 640 basepairs of cytochrome oxidase subunit I mtDNA show that C. fecunda nests within a paraphyletic C. dilatata and that the three successive sister groups are all species with direct development. The direct developing embryos of C. dilatata retain a velum with a functional oposed band ciliary mechanism and a complete gut. These morphological and phylogenetic data both support the scenario in which the planktotrophic C. fecunda arose from the direct developing C. dilatata.