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Speaker 1: Welcome to brain stuff from how stuff works, Hey, brain stuff,

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Speaker 1: Lauren Vogel bomb Here. Snails are very attached to their shells. Literally,

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Speaker 1: these slow moving mollusks grow protective shells to which they

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Speaker 1: are physically connected. Eviction means death. No snail can survive

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Speaker 1: being torn away from its private calcified fortress. But how

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Speaker 1: exactly do snails shells develop and what sets them apart

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Speaker 1: from other types of animal armor? Before we get to

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Speaker 1: that A bit of snail one oh one. The total

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Speaker 1: number of snail species could be as high as forty

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Speaker 1: three thousand. Most of us are familiar with land based

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Speaker 1: varieties or those that live in ponds, but marine snails

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Speaker 1: also exist, and when it comes to procreation, certain species

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Speaker 1: reproduce sexually, while others are self fertilizing hermaphrodites. Whatever gets

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Speaker 1: the job done right. They all do have one thing

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Speaker 1: in common, though. Snails all hatch from eggs. Generally, the

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Speaker 1: parents lay these eggs in loo soil or affix them

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Speaker 1: to rocks, though a few species are over viviporous, meaning

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Speaker 1: their eggs hatch inside the mother's body. The newborns then

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Speaker 1: squirm out and face the world, but this brings us

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Speaker 1: back to that question about the shell. It's during the

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Speaker 1: gestation period that a snail's shell begins to form, and

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Speaker 1: here's where the mantle comes in. This is a crucial

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Speaker 1: organ possessed by mollusks such as snails. Its function is

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Speaker 1: making and developing shells. Calcium carbonate is the primary ingredient

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Speaker 1: in snail shells. Those small amounts of protein also go

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Speaker 1: into the mix, so in order to build these shells,

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Speaker 1: the mantle creates an electric current that helps the organism

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Speaker 1: push calcium ions into the right places. Before hatching, a

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Speaker 1: baby snail grows a protoconch, the first component of its shell.

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Speaker 1: Once our little snail leaves the egg, healthy eating becomes

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Speaker 1: a priority. The mantle will require additional calcium to strengthen

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Speaker 1: and expand the shell. Instinct compels newborn snails to devour

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Speaker 1: what's left of the calcium rich egg that they've just escaped,

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Speaker 1: and thus begins a lifelong habit. Snails of all ages

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Speaker 1: and sizes need to keep eating foods that are high

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Speaker 1: in calcium. This is one reason why snails are so

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Speaker 1: often considered pests. A few of them like to chow

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Speaker 1: down on spinach, broccoli, turnip, and other calcium loaded crops.

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Speaker 1: They can also get their calcium fixed by swallowing soil

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Speaker 1: or gnawing on limestone. That protoconch comes with a small

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Speaker 1: opening or mouth. The mantle organ adds new layers of calcium,

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Speaker 1: carbonate and proteins to the mouth from below. As that

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Speaker 1: new material hardens at the mouth, the shell grows, Spiraling

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Speaker 1: coils form around the protoconch, which gradually spins around and around,

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Speaker 1: becoming the apex, or uppermost tip of the snails widening shell.

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Speaker 1: Depending on the species, the protoconch will either remain there

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Speaker 1: permanently or break off at some point. Snail shells always

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Speaker 1: coiled to the right or to the left. That's another

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Speaker 1: thing that varies from species to species. Most snails possess

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Speaker 1: right word pointing shells, but there are a few you

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Speaker 1: whose shells orient towards the left, and in some species

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Speaker 1: these shells can coil in either direction. If you were

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Speaker 1: to cut open a snail shell, you've noticed several main

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Speaker 1: layers in the cross section. At the surface, there's the pereostracum,

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Speaker 1: a thin outer layer usually made with organic material. Below that,

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Speaker 1: you've got a layer of hard calcium sitting atop a

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Speaker 1: blanket of noker that's a resilient composite material better known

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Speaker 1: as mother of pearl. One thing you won't find, however,

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Speaker 1: is a network of nerves or blood vessels. Turtle shells, meanwhile,

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Speaker 1: contain both. In most cases, the shells we find in

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Speaker 1: these much adored reptiles are really networks of modified bones

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Speaker 1: like ribs, vertebra, and pelvic elements that have been fused

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Speaker 1: together and covered by hard plates. When a turtle's shell

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Speaker 1: gets cracked, the body dispatches cells to try and repair

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Speaker 1: the damage. Snails have a different method for fixing cracks.

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Speaker 1: Calcium and protein secretions from their mantles can be used

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Speaker 1: to help strengthen the damaged areas. Of course, having a shell,

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Speaker 1: even one that can heal it self, does not guarantee safety. Ironically,

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Speaker 1: a lot of nesting birds like to eat snails because

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Speaker 1: of their protective shells and the calcium that they contain.

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Speaker 1: To keep one step ahead of predators, many snails have

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Speaker 1: seriously up to their self defense game. For example, the

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Speaker 1: deep sea species Chrystomalin squire if um is covered in

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Speaker 1: iron sulfide, giving the entire animal a strange metallic appearance

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Speaker 1: and acting basically like battle armor. In fact, researchers have

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Speaker 1: looked into the possibility of using this animal's amazing exterior

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Speaker 1: to develop better armor for human soldiers. Today's episode was

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Speaker 1: written by Mark Vansheny and produced by Tyler Clang with

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Speaker 1: the kind engineering assistance of Ramsay youngt. For more on

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Speaker 1: this and lots of other perhaps slimy but battle ready topics,

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Speaker 1: visit our home planet, how stuff works dot com.