The general consensus has been that the shells of mollusks form outside of cells. Akin to bone formation in vertebrates, an organic matrix is secreted by cells and the inorganic material is deposited within this matrix in an organized way. Andrew Mount, A.P. (Hap) Wheeler, Rajesh Paradkar, and Dennis Snider have now found convincing evidence that blood cells (specifically a class of granulocytic hemocytes) may be directly involved in shell crystal production for oysters.