The ability of a biological system to drive the formation of a microstructure as complex and ordered as the molluscan shell is of immense interest to the fields of nanotechnology and biomedicine. Although recent studies have greatly expanded our knowledge of the genes involved in shell formation, the mechanism by which matrix proteins are regulated and directed to the appropriate region of the shell, a process critical for microstructure control, is still obscure. The formation of microstructure-specific compartments within the extrapallial cavity may be the outcome of precise regulation of the vesicle trafficking of shell components within secretory cells at the mineralization front and/or the overall organization and morphology of the mantle itself. Here, we investigate the ultrastructure of the mantle of the gastropod Haliotis asinina as current models put forward to describe molluscan shell formation are primarily based on observations from bivalves despite crystallographic and molecular studies indicating large differences between molluscan classes. We find that the H. asinina mantle is structurally complex and comprised of novel cells packed with a diversity of vesicle types consistent with a complex system to control the secretion of the shell matrix and associated factors.