Mollusc shells are diverse in shape and size. They are created by a shell epithelium which secretes a chitinous periostracum membrane at the growing edge of the shell, and then coordinates biomineral deposition on the underside of this membrane. Although mollusc shells are important for studying the evolution of morphology, the molecular basis of the shell development is poorly understood. In this paper, we investigate genes involved in the shell development of the gastropod mollusc Tritia (previously known as Ilyanassa). We characterize the contributions of the 2d micromere to the shell and other non-shell structures. We identify eight shell-specific genes and five non-shell specific genes by comparing the transcriptomes of wild-type and 2d ablated embryos. Morpholino knockdown of one of the shell-specific genes, ToChitin-binding domain-containing (ToChitin BD), results in shell defects. The chitinous periostracal membranes in ToChitin BD morpholino knockdown embryos lose their well-defined edge and peroxidase gradient.