The objective is a new understanding of the origin of the earliest Mollusca and related invertebrates. Recent advances in the study of sclerite-bearing animals from the Cambrian provide an opportunity to investigate the relationship between primitive spiculose molluscs (aplacophorans and chitons) and related soft- bodied phyla (annelids, nemertines, sipunculans). These Cambrian fossils appear to bridge some of the morphological gaps between living phyla and to suggest how mineral skeletons might have first evolved within the Mollusca. We intend to obtain 18S rRNA sequences from living spiculose molluscs in order to test whether aplacophorans are the most primitive living molluscs or are secondarily simplified. Furthermore, we plan to investigate the crystallography of polyplacophoran plates to test the hypothesis that chiton crossed-lamellar aragonite is different from and therefore not homologous to the crossed-lamellar structure of the shelled (conchiferan) molluscs. At the same time we intended to compare the microstructures of molluscan spicules with a variety of sclerites extracted from Cambrian limestones. This work is expected to provide new insights into the early history of the Mollusca and the evolution of the Metazoa as a whole.
