What is a seashell?

0:46 Welcome to Sciences Not Boring by kidopoly.com. I'm Mira. And I'm Finn. Before we dive in, we have some huge shout-outs today. A big hello to Elliot, who is four and turning five, and excited to start school. Elliot asked how baby snails grow their shells and whether they ever shed them. This one is for you, Elliot.

1:08 And a very happy 8th birthday to Everly, who is celebrating with her sister Palmer at Disneyland. Have the most magical birthday adventure, Evelie. If you haven't already, tap follow wherever you're listening so you never miss an episode. Now, close your eyes, picture you're walking on the beach, you hear the waves crashing on the shore, you feel the warm sand between your toes, and you bend down to pick up a beautiful, swirly seashell.

1:36 I love finding shells. I have a whole collection of them, but I always make sure nobody is home first. Good idea, because that shell wasn't just a rock shaped by the ocean. It was built, molecule by molecule, layer by layer, by a squishy sea creature. Wait. Built? Like with tiny underwater tools? No tools required.

2:01 Today we're talking about how sea creatures build their own armour, including a giant clam that weighs up to 550 pounds. 550 pounds? That's heavier than a grizzly bear. Exactly! It's called Tridacna Gigus, and it lives in the shallow coral reefs of the South Pacific. Get ready to learn the secrets of the shell builders.

2:24 Okay, so if shells aren't rocks, what exactly are they? They are the outer skeletons of animals called molluscs. That includes snails, clams, oysters, and those ancient-looking nautiluses with the striped shells. But when I touch a snail in the garden, it feels so slimy and soft. How do they make something so rock hard?

2:46 It all starts with a special organ called the mantle. It's like a fleshy, magical 3D printer wrapping around the animal's body. A 3D printer made of animal parts? That sounds a little weird. It is weird, but it's brilliant. The mantle acts like a tiny chemistry lab. It pulls in ingredients from the ocean water and the food the mollusk eats.

3:10 What kind of ingredients? Like salt and sand? Mostly calcium and carbonate ions. The ocean is full of dissolved minerals. When the mantle mixes these specific ingredients together, it secretes a special liquid that crystallises into solid calcium carbonate. Whoa, so they basically sweat out liquid rock and it hardens into armour.

3:34 That is a perfect way to describe it. First, the mantle creates a microscopic protein scaffolding, kind of like the steel beams construction workers use inside a skyscraper. Oh, to give it shape and strength. Exactly. Then it fills the gaps in that scaffolding with liquid crystals that harden layer by layer, building the shell from the inside out.

3:58 Where does this happen? Just in the ocean? Everywhere, in freezing deep ocean trenches, boiling hydrothermal vents, shallow coral reefs, freshwater lakes, and even your own backyard. Mollusks have conquered almost every habitat on Earth thanks to this incredible shell-building trick. This brings us to Elliot's amazing question.

4:22 Elliot wants to know how baby snails grow their shells and whether they shed them. Yeah, like how a snake sheds its skin, or a tarantula malts its exoskeleton. I bet baby snails just pop out, leave their old shell behind, and find a new house when they get too big. Actually, no! This is the most mind-blowing part.

4:45 A snail is born already wearing its tiny, almost transparent baby shell. Wait, really? It hatches out of the egg carrying its house? Yes, and they never ever shed them. A snail's shell is permanently attached to its body by strong muscles and tissue. Oh no, so if someone tries to pull a snail out of its shell to help it.

5:07 Exactly, Finn. You should never try to pull a snail out. You can't take a snail out of its shell without hurting it badly. The shell is literally part of their body. Oh, phew, good to know. But wait, if they never leave it, how do they get bigger? They can't just squeeze into a tiny baby shell forever.

5:27 That's where the magical mantle comes in again. As the snail grows, the mantle pushes out new calcium carbonate liquid right at the opening of the shell. You mean the lip, where the snail's little head pokes out? Yep, it adds new material to the edge. The shell grows in a spiral shape, wrapping around itself as it gets longer and wider.

5:48 If you look closely at a snail shell, you'll see tiny lines or ridges spiralling all the way up to the point. Oh, the growth rings, like the rings inside a tree trunk. Exactly like a tree. Every one of those rings is a new layer the snail added as it grew. They just keep building the doorway wider and wider for their whole lives, expanding their house room by room.

6:12 Okay, so a garden snail builds a small house. But what about the really big ones? Oh, you mean like the tridacnogigus? The giant clam. How giant is giant? Because giant to a bug is very different than giant to me. Try over four feet wide, and they can weigh up to 550 pounds. 550 pounds? You weren't kidding about the grizzly bear.

6:38 How does a clam make that much shell? It must eat so much calcium. It uses time, patience, and a little help from the sun. Giant clams can live for over a hundred years. They sit on the flat coral sand, opening their beautiful brightly coloured mantles to the sunlight. Wait, they sunbathe? Yes. They have tiny algae living inside their tissue that make food from the sun, sharing the energy with the clam.

7:04 The clam uses that energy to filter ocean water, absorbing calcium and slowly building that massive shell for a century. I am definitely not picking one of those up on the beach. But wait, if all these molluscs make their own shells, what about hermit crabs? Ah, hermit crabs are the rule breakers of the beach.

7:23 They belong to an entirely different family. They are crustaceans, related to shrimp and lobsters. So they don't have a mantle. They can't 3D print their own shell. Nope. They have very soft, squishy abdomens that need protection from predators and the hot sun. So they have to scavenge for empty snail shells to live in.

7:43 They're real estate agents. They just find an abandoned house and move in. Yes, but here's the wild part. When a hermit crab outgrows its shell, it has to find a bigger one. Sometimes they form what marine biologists call a vacancy chain. What's a vacancy chain? When a big, perfect shell washes up, crabs of all sizes will gather around it.

8:05 They literally line up from biggest to smallest, carefully inspecting each other's shells. Wait, they actually stand in line like they're waiting for a roller coaster. Yes. When the biggest crab decides to move into the new empty shell, the next crab takes the one they just left. And so on down the line, in a massive, rapid-fire shell swapping party.

8:26 That is the coolest thing ever. A huge crab swap me. Everyone gets a brand new house. It really is. But building these original shells takes a lot of hard work for the molluscs. And sadly, the ocean environment is changing. How so? Is the water getting too hot? The temperature is rising, but there's another problem called ocean acidification.

8:49 Because of extra carbon dioxide pollution in the air, the ocean is absorbing huge amounts of that gas. And that changes the water. Right, it changes the ocean's chemistry. The water becomes slightly more acidic, which makes it much harder for molluscs to pull those precious calcium and carbonate ingredients out of the water.

9:09 Oh no! So it's like they're trying to build a strong brick house, but someone hid all the bricks. Exactly! In some places, shells are even becoming thinner and more fragile. That's why scientists are working so hard to protect our oceans and reduce pollution. So these amazing creatures can keep building.

9:28 I really hope they figure it out. The giant clams need to keep making those 550 pound armour plates. Me too! Now, are you ready for some mind-blowing fun facts to wrap up the story? Always! Hit me with the facts! Did you know the inside of many shells, like oysters and abalone, is lined with a smooth, glowing material called Naker or Mother of Pearl.

9:52 Is that the shiny rainbow stuff that looks like liquid pearl? Yes, it's actually made of microscopic hexagonal plates stacked like bricks, glued together with elastic proteins. It's so incredibly strong that scientists are studying it to try and invent better armour and building materials for humans.

10:10 Wow, so a squishy oyster is basically a master engineer. We're copying their homework. Totally! And here's another one. A scientist named Professor Derek Moulton at the University of Oxford studies the mathematical forces of shells. Wait, people study the math of shells. Yes, he found that just a few simple mathematical rules control how almost every shell in the world twists, flares, and coils as it grows.

10:38 Nature is full of math. Alright, Finn, quiz time. Are you ready? Okay, I'm ready. Let's see if my brain absorbed all these facts. First question. What is the name of the special organ in a mollusk that acts like a 3D printer to build its shell? Next one. Do baby snails ever shed their shells when they grow bigger?

11:07 Question three. We talked about the Tridacne gigus, the giant clam. What is the maximum weight it can reach? Here's number four. Why do hermit crabs need to steal empty snail shells instead of growing their own? Last question. What do scientists call it when hermit crabs line up from biggest to smallest to trade shells?

11:40 Great job! Let's see how you did and go through the answers. The first answer is the mantle. It's the squishy tissue that secretes liquid calcium carbonate. For question two, no way. Snails never shed their shells. They just add layers to the opening and the shell grows with them. Number three, the answer is up to 550 pounds, which is as heavy as a grizzly bear.

12:10 Question four. Because hermit crabs are crustaceans with soft bodies, and they don't have a mantle to 3D print their own shell. And the final answer is a vacancy chain. Phew! I think I did pretty well on that quiz. I'll never look at a seashell the same way again. Me neither. It's amazing to think that every single empty shell you find, washed up on the beach, was once carefully built by a brilliant little architect.

12:38 I'm just going to be super careful where I step. I definitely don't want to trip over a 550-pound giant clam. Haha, I think you'd spot that one coming, Finn. Hey, if you love discovering amazing facts with us, please leave a five-star review. Yeah. Tell us what you think is the coolest shell builder in the ocean.

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13:20 Keep exploring and keep wondering. See you next time on Science is Not Boring. Bye everyone!