A key question in the field of developmental biology is what fundamental mechanisms are responsible for specifying different cell fates during embryogenesis? A related question in the field of evolutionary biology is how have these mechanisms been deployed to generate the tremendous array of animal phyla and their distinctive body plans? Large gaps in our knowledge are due to the fact that only a small number of animal models have been chosen for such studies. This research focuses attention on representatives of a poorly studied group of organisms, the spiralian lophotrochozoans, which encompass nearly one-third of all living animal phyla (including molluscs, annelids, etc.). The proposed studies deploy a powerful combination of modern cell and molecular biology approaches to reveal fundamental information about basic mechanisms that ultimately control the differentiation of embryonic cell fates and axial properties, using an ideal spiralian model system, the snail Crepidula. More specifically, this research will uncover key embryonic cell signaling events and the underlying molecular pathways that ultimately specify the fates of cells during development. Other studies suggest that many of these processes have been conserved across the animal kingdom, including in humans. The findings of this study will be compared with those gained from other animal systems to understand the degree to which these events have changed over the course of evolutionary history. This research has a broader impact not only in terms of the science, but also in education. NSF funding allows the continued training of future generations of scientists and teachers, which include undergraduate and graduate students, who will work on these projects.