15-P034 Expression of a Coe gene in the developing nervous system of the annelid Platynereis dumerilii

extant limpet. In addition, bivalves also acquired a novel structure, adducter muscle to close the separated shell plate. Because the two novel structures, the separated shell plate and the adducter muscle appear early embryonic stage, their evolution should be understood as a modification of early development. To understand the evolution of bivalve bodyplan, we have traced the cleavage pattern of the Japanese purple mussel, Septifer virgatus. We found that the stereotypic cleavage pattern of shell plate precursor cells were observed in this species, suggesting that the cleavage pattern itself is tightly regulated because it is essential for the development of bivalve bodyplan. We also observed the expression pattern of dpp homolog which is involved in shell formation in gastropod. In addition, we observed the development of novel cell population of adductor muscle by using some molecular markers.