Formation of the shell The gastropod shell has three major layers secreted by the mantle. The body of the snail contacts the innermost smooth layer that may be composed of mother-of-pearl or shell nacre, a dense horizontally packed form of conchiolin, which is layered upon the periostracum as the snail grows.Click to see full answer. Hereof, what are gastropods shells composed of?In land snails the shell is an essential protection against the sun, and against drying out. The gastropod shell has several layers, and is typically made of calcium carbonate precipitated out into an organic matrix. It is secreted by a part of the molluscan body known as the mantle.Additionally, how do snails build their shells? A baby snail usually begins its calcium-rich diet by eating the shell of the egg it hatched from, a convenient source of nutrients. As the snail continues to grow, its shell grows with it. The snail produces new shell material, like the soft material of its protoconch, that expands its shell and then hardens. Simply so, how many shells do gastropods have? Most shelled gastropods have a one piece shell, typically coiled or spiraled, at least in the larval stage.What is the oldest part of the shell in gastropods?In anatomy, an apex (adjectival form: apical) is part of the shell of a mollusk. The apex is the pointed tip (the oldest part) of the shell of a gastropod, scaphopod, or cephalopod.