WEBVTT - BrainStuff Classics: How Do Snails Grow Their Shells?

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<v Speaker 1>Welcome to brain Stuff production of I Heart Radio. Hey

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<v Speaker 1>brain Stuff, Lauren vogle bomb here with a classic episode

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<v Speaker 1>for you. This one deals with the exoskeletal science of

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<v Speaker 1>one of my personal favorite animals, snails. I keep some

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<v Speaker 1>aquatic snails as pets and watching them hatch and grow

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<v Speaker 1>is absolutely wild, if not exactly fast going. Here's how

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<v Speaker 1>it works, Hey brain Stuff, Lauren voge bomb here. Snails

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<v Speaker 1>are very attached to their shells. Literally, these slow moving

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<v Speaker 1>mollusks grow protective shells to which they are physically connected.

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<v Speaker 1>Eviction means death. No snail can survive being torn away

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<v Speaker 1>from its private calcified fortress. But how exactly do snails

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<v Speaker 1>shells develop and what sets them apart from other types

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<v Speaker 1>of animal armor. Before we get to that a bit

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<v Speaker 1>of snail one oh one, the total number of snail

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<v Speaker 1>species could be as high as forty three thou. Most

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<v Speaker 1>of us are familiar with the land based varieties or

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<v Speaker 1>those that live in ponds, but marine snails also exist.

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<v Speaker 1>And when it comes to procreation, certain species reproduce sexually,

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<v Speaker 1>while others are self fertilizing hermaphrodites. Whatever gets the job

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<v Speaker 1>done right. They all do have one thing in common,

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<v Speaker 1>though snails all hatch from eggs. Generally, the parents lay

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<v Speaker 1>these eggs in loose soil or affix them to rocks,

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<v Speaker 1>though a few species are over viviparous, meaning their eggs

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<v Speaker 1>hatch inside the mother's body. The newborns then squirm out

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<v Speaker 1>and face the world. But this brings us back to

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<v Speaker 1>that question about the shell. It's during the gestation period

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<v Speaker 1>that a snail's shell begins to form, and here's where

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<v Speaker 1>the mantle comes in. This is a crucial organ possessed

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<v Speaker 1>by molluscs such as snails. Its function is making and

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<v Speaker 1>developing shells. Calcium carbonate is the primary ingredient in snail shells.

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<v Speaker 1>Those small amounts of protein also go into the mix,

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<v Speaker 1>so in order to build these shells, the mantle creates

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<v Speaker 1>an electric current that helps the organism push calcium ions

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<v Speaker 1>into the right places. Before hatching, a baby snail grows

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<v Speaker 1>a protoconch, the first component of its shell. Once our

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<v Speaker 1>little snail leaves the egg, healthy eating becomes a priority.

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<v Speaker 1>The mantle will require additional calcium to strengthen and expand

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<v Speaker 1>the shell. Instinct compels newborn snails to devour what's left

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<v Speaker 1>of the calcium rich egg that they've just escaped, and

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<v Speaker 1>thus begins a lifelong habit. Snails of all ages and

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<v Speaker 1>sizes need to keep eating foods that are high in calcium.

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<v Speaker 1>This is one reason why snails are so often considered pests.

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<v Speaker 1>A few of them like to chow down on spinach, broccoli, turnip,

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<v Speaker 1>and other calcium loaded crops. They can also get their

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<v Speaker 1>calcium fixed by swallowing soil or gnawing on limestone. That

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<v Speaker 1>protoconch comes with a small opening or mouth. The mantle

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<v Speaker 1>organ adds new layers of calcium, carbonate and proteins to

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<v Speaker 1>the mouth from below. As that new material hardens at

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<v Speaker 1>the mouth, the shell grows, Spiraling coils form around the protoconch,

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<v Speaker 1>which gradually spins around and around, becoming the apex, or

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<v Speaker 1>uppermost tip of the snails widening shell. Depending on the species,

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<v Speaker 1>the protoconch will either remain there permanently or break off

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<v Speaker 1>at some point. Snail shells always coiled to the right

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<v Speaker 1>or to the left. That's another thing that varies from

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<v Speaker 1>species to species. Most snails possess right word pointing shells,

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<v Speaker 1>but there are a few whose shells orient towards the left,

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<v Speaker 1>and in some species. These shells can coil in either direction.

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<v Speaker 1>If you were to cut open a snail shell, you've

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<v Speaker 1>noticed several main layers in the cross section. At the surface,

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<v Speaker 1>there's the peiostracum, a thin outer layer usually made with

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<v Speaker 1>organic material. Below that, you've got a layer of hard

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<v Speaker 1>calcium sitting atop a blanket of noker. That's a resilient

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<v Speaker 1>composite material better known as mother of pearl. One thing

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<v Speaker 1>you won't find, however, is a network of nerves or

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<v Speaker 1>blood vessels. Turtle shells, meanwhile, contain both. In most cases,

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<v Speaker 1>the shells we find in these much adored reptiles are

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<v Speaker 1>really networks of modified bones like ribs, vertebra, and pelvic

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<v Speaker 1>elements that have been fused together and covered by hard plates.

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<v Speaker 1>When a turtle shell gets cracked, the body dispatches cells

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<v Speaker 1>to try and repair the damage. Snails have a different

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<v Speaker 1>method for fixing cracks. Calcium and protein secretions from their

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<v Speaker 1>mantles can be used to help strengthen the damaged areas.

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<v Speaker 1>Of course, having a shell, even one that can heal itself,

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<v Speaker 1>does not guarantee safety. Ironically, a lot of nesting birds

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<v Speaker 1>like to eat snails because of their protective shells and

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<v Speaker 1>the calcium that they contain. To keep one step ahead

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<v Speaker 1>of predators, Many snails have seriously up to their self

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<v Speaker 1>defense game. For example, the deep sea species Chrystomalin squareferum

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<v Speaker 1>is covered in iron sulfide, giving the entire animal a

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<v Speaker 1>strange metallic appearance and acting basically like battle armor. In fact,

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<v Speaker 1>researchers have looked into the possibility of using this animal's

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<v Speaker 1>amazing exterior to develop better armor for human soldiers. Today's

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<v Speaker 1>episode is based on the article how does Snails get

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<v Speaker 1>their shells? On how stuff works dot Com, written by

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<v Speaker 1>Mark Mancini. Brain Stuff is production of I Heart Radio

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<v Speaker 1>in partnership with how stuff works dot Com, and it's

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<v Speaker 1>produced by Tyler clay Or. More podcasts my heart Radio,

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