How Do Snails Get Their Shells?

[upbeat music] A snail starts making its shell before it even hatches.

So when a tiny snail comes out of its egg, it already has a teeny-tiny shell on its back.

You know how a snail shell looks like a spiral? Well, the oldest part of a snail shell is way up near the tiny tip of the spiral.

That part was there when the snail was much, much smaller, right from the beginning.

But snails are hard, right? So how does the shell get bigger? Does the shell stretch as the snail grows? [snail stretching] Nope.

The snail actually adds new shell to the shell it already has.

[gentle music] And there is one particular part of the snail's body that does most of that work.

It's called the mantle.

Can you say the mantle? The mantle is soft tissue that sits underneath the shell.

As the snail grows, the mantle releases the materials needed to build more shell.

[snail eating] One of the most important of those materials is something called calcium carbonate.

Can you say calcium carbonate? Now, you might not have realized it, but you've probably seen calcium carbonate before.

It's the main material in things like limestone and eggshells.

[eggshells cracking] A snail gets the calcium it needs from its food and from materials in its environment.

Its mantle uses that calcium to help build those hard layers of shell.

[snail eating] So how does the mantle add new shell to the body? Well, most of the shell's growth happens around the opening.

And by opening, I mean where the snail's body comes out of the shell.

The mantle adds new material along that edge, and little by little, the opening gets larger and the shell grows outward.

Isn't that cool? And that's what creates those bigger and bigger curves in a spiral shell.

[gentle music] So if you could somehow watch a snail shell growing in really, really, really fast motion, [shell whooshing] the little spiral at the top would never actually disappear.

It would stay there while newer and larger sections were added around the opening.

The mantle can also add shell material to the inside, making parts of the shell thicker and stronger, and sometimes it can even help repair damage.

If a shell gets a small crack or chip, the mantle may be able to [snail eating] lay down new material underneath the damaged area.

Now, how well that works depends on where the damage is and how bad it is.

[chuckles] A snail's body is firmly attached to the inside of its shell by muscle, and some of its organs are actually inside the coiled part of the shell.