They're born with tissue that is "pre-determined" to become the shell. Then they build them up, using calcium from what they eat
How do snails get their shells?
Hi, Puneter hunter Snail shell is part of its body it gives it the shape and security as it mover around. The snail would be slug if it didn't have an external shell. The shell is the equivalent of our skeleton. A snail is an invertabrate and has traded it spine or back bone for the shell. The shell also provides the animal with security once inside the shell it is safe from predation by birds for example. They feel hurt when their shell is crushed so please don't step on them a beer trap is a kinder way of killing them off. In France they eat snail with a sauce.