The mollusk shell mobilizes calcium from environment for skeletal mineralization. This occurs through synthesizing solids in solution in the presence of organic molecules of specific interior regions of the conch shell. The ultrastructure of the Hemifusus tuba conch shell living in the Huang/Bo sea area is investigated in the paper. It is shown that the composition and microstructure of the mollusk shell vary in different positions. The prodissoconch shell consists only of aragonite with the crossed-lamellar microstructure. While the spiral shell and the body shell of the Hemifusus tuba conch shell are composed of one calcite layer and several aragonite layers. The calcite layer consists of cylindrical grains, but the aragonite layers are crossed-lamellar ultrastructure. The margin of shell aperture is only composed of calcite with cylindrical grains. This natural optimization of the shell microstructure is intimately due to the growth of the organic matrix. The process of growth allows a constant renewal of the material, thus enabling the functional adaptation of the shells.