[SciShow kids intro plays]

Jessi: When you think of a shark, what do you picture in your mind? Do you think of a big fin sticking out of the water? Or maybe a set of huge, sharp teeth? Sharks are some of the most famous animals in the ocean. But do you know what makes a shark... a shark?

Well, for one thing, all sharks are fish. That might not surprise you, since they live and swim in the water. But sharks are a special kind of fish. One of the things that makes them different from other fish, like goldfish, is that sharks have a special skeleton! Our skeletons are made of bone, and so are the skeletons of most kinds of fish.

But a shark’s skeleton isn’t made of bone, it’s made of cartilage. And you have cartilage in your body, too! You can feel it right now! Touch the tip of your nose. Wiggle it around. How does it feel? What about your ear? Can you bend it? You sure can, because the tip of your nose and your ear aren’t filled with bone. They’re filled with cartilage! Cartilage is a lot lighter than bone, and it bends easily, so having a skeleton made of this stuff helps sharks swim farther, and faster, than if their skeletons were made of bone!

Now let’s look at another body part that sharks are famous for: their teeth! Have you ever lost a baby tooth? And then an adult tooth grew in? Well, sharks lose their teeth all the time throughout their entire lives... and they just keep growing new ones! How can they do that? You and I have just one row of teeth in our mouths. But sharks have lots of rows of teeth, on the top and the bottom. So when a shark looses a tooth, another tooth that’s right behind it can just move on up to take its place! Because they always have new teeth to replace the old ones, some sharks can lose thousands of teeth during their lives!

Alright, the next cool thing about sharks? Their skin! If you could rub the skin of shark, you’d find that it would feel smooth if you ran your hand in one direction. But if you rubbed your hand the other way, it would feel rough, like a cat’s tongue. That’s because a shark’s skin is covered in tough, bony scales that actually look a little like tiny teeth! These little scales are stacked on top of each other like tiles on a roof. This helps sharks swim through the water quickly and quietly.

So, those are some of the things that all sharks have. But, there are over 450 types of sharks in the world, and that means a lot of differences, too! Take a look at this one. It’s called a whale shark, and it’s the biggest shark there is -- in fact, it’s the largest fish in the whole world! Whale sharks can grow to be as long as a school bus! But even though they’re so big, they eat tiny plants, and super small animals called plankton, that float in the water.

But not all sharks are as big as the whale shark-- some can also be tiny! Meet the dwarf lantern shark. It's so small it could fit in my hand! This shark lives in the deep ocean, where there’s very little light, so it has big eyes to help see in the dark. Plus, it has a really neat feature -- it has special organs on its belly, fins, and tail that actually glow! Scientists think this might help the lantern shark lure in prey for it to eat. Plus, when it’s in shallower water where there’s more light, these glowing lights can help it blend in, to avoid predators.

Finally, I’d like you to meet a very special shark. Say hello to the Greenland shark! This big shark spends most of its time swimming in very cold water, hanging out near the seafloor, looking for an easy snack. But scientists have recently discovered something amazing about these animals: Greenland sharks can live to be up to 400 years old! Of all the animals in the world with backbones, known as vertebrates, Greenland sharks live the longest -- at least, that we of. But scientists are still discovering new kinds of sharks all the time! So, who knows what kinds of super sharks are still out there waiting to be found?

What’s your favorite animal? Do you want to learn more about it? Just ask a grownup to help you, and leave a comment below, or send us an email to kids@thescishow. com! We’re excited to hear from you! Oh! And we're also really excited because we’re making some changes to the fort. So stay tuned, and we'll share a few surprises with you in the upcoming weeks! Thanks, and we’ll see you next time, here at the fort!