A snail's shell is secreted by glands in its mantle rim and consists of three layers:
- hypostracum - the innermost layer, closest to the snail's body
- ostracum - middle, shell building layer, consists of prism-shaped calcium carbonate crystals and organic (proteid) molecules
- periostracum - outermost layer, consists of conchin (a mixture of organic compounds), gives the shell color
The snail's shell serves to protect its internal organs, prevent water loss, provide shelter from cold, and protect the snail from predators.