The nervous systems of molluscs show a diversity which surpasses any other phylum, except perhaps the chordates. The brains and behaviours of cephalopods like the octopus were subjects of fascination for Aristotle, while those of sedentary chitons can be described only as rudimentary at best. And yet, we currently know very little about how the molluscan nervous system develops or how such diversity is generated through evolution. Moreover, knowledge of neural development derived from model organisms such as flies, worms and certain vertebrates appears inadequate to resolve this issue. This application proposes two lines of research aim at better understanding neural evolution and development within the molluscs. The first line will investigate the olfactory system and look for the basic units of sensory processing (glomeruli) as described in arthropods and vertebrates but largely unknown outside these two groups. Work on molluscs will not only inform us about how olfaction may have evolved in these animals but may provide insights into our own sense of smell. The second line involves investigation of the larval nervous system, which plays a critical role in early life and provides a scaffold on which the adult nervous system is built. The larval nervous system of molluscs is known to share similarities with larval nervous systems from across the animal kingdom and thus serves as a basis for comparison of animals with otherwise diverse body forms. Our work focuses on identification and morphology of cells which use acetylcholine and histamine as transmitters, and then examines their roles in behaviours that allow larvae to orient to chemicals, light, currents and gravity. Both lines of research will depend upon the use of multiple, combinational staining techniques coupled with high resolution microscopy and 3D reconstruction. As both the most varied and also the largest phylum in the Lophotrochozoa, the molluscs offer an important and unique perspective from current model species. While aimed largely at a better understanding of the diversity of life around us, the work also has implications for understanding larval and adult molluscs as major components of our ocean ecosystems and even as prized foods from aquaculture.