• Like oysters, mussels, and scallops, clams are bivalve mollusks – aquatic invertebrates encased by a shell made of two valves.
  • Inside their shell, you’ll find some truly bizarre anatomy. They have a retractable foot, for example, which they use to bury themselves underground.
  • Research has shown that razor clams can use their foot to liquefy the ground around them, essentially turning it into quicksand.
  • Giant clams farm microalgae. In exchange for a place to live, the algae provide the clams with byproducts of photosynthesis, such as sugars, allowing them to grow into giants.
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What’s inside a clam? A retractable foot, a siphon for sucking up water, powerful muscles, and, sometimes, a pearl. And you thought oysters were fancy.

Following is the transcript of the video.

Narrator: What you’re looking at is a clam’s foot. That’s right, clams have a foot. And some species can extend it several inches. But as it turns out, a foot is just one of the many bizarre features you’ll find inside a clam. Like oysters and mussels, clams are bivalves, a kind of mollusk that’s encased in a shell made of two valves, or hinging parts. And that shell comes in all different sizes.

There are small clams, like these, which are often used for cooking. And then there are giant clams, which can grow more than a meter long and weigh as much as 250 kilograms. But no matter their size, clams have some truly bizarre stuff going on inside. And to get a closer look, we went clamming.

Benji Jones: Oh, God. [laughing]

Narrator: That's marine biologist Soren Dahl, who took us clamming on Long Island. At first, we didn't have much luck.

Benji: I got one, but it looks like it's dead.

Soren Dahl: Old shell.

Benji: Oh, I got a crab.

Narrator: Then we stumbled upon what's known as a honey hole. It's basically a clammer's code word for jackpot.

Benji: Hey! I got two! [laughing]

Soren: All right!

Narrator: And in the end, we found about a dozen hard clams.

Benji: This right here is my recently collected, my recently collected clams, and I have a lot of them.

Narrator: Now, to see what's inside, you can't exactly pry one open with your bare hands. And that's thanks to these two muscles. They run from the inside of one shell to the other, and when clams sense a threat or find themselves out of water, they contract, causing the clam to, you know, [snapping] clam up. So, to get one open, you need to cut through those muscles.

Soren: Now, you have your, this is your hard-shell clam.

Benji: Both of, so those two muscles together create a muscle that goes from here to here?

Soren: Yep, this goes from this side to that side.

Narrator: And what about that strange foot?

Soren: This is the foot, right here.

Narrator: So, it might not be as impressive as this, but that's just because here the foot is retracted. Soren: And they'll extend this out of the clam, and they can push themselves along the bottom and use it to dig a hole to help bring themselves into, like, a burrow.

Narrator: And some clams are particularly dexterous with their foot. The razor clam, for example, can bury itself 70 centimeters underground. It uses rapid movements of its foot to fluidize the ground around it, essentially turning it into quicksand. But if you think clam feet are bizarre, check out this thing: the siphon. Siphons are essentially two connected straws that clams stick out of their shells. One pulls in water, which contains food particles and oxygen, and the other expels waste. And none is more impressive than the one belonging to the geoduck clam.

It's so big the clam can't even close its shell. While siphons allow clams to eat and breathe, some clams have another, more advanced tactic for getting nutrients. Instead of just sucking food out of the water, giant clams farm it themselves. Like coral, they have a symbiotic relationship with microalgae.

The clams provide algae with a place to live and photosynthesize, and in exchange, algae gives the clam byproducts of photosynthesis, such as sugars, which enables the giant clams to grow, you know, giant. Now, on rare occasions, there's something else you might find inside a clam: a pearl. That's right, oysters aren't the only pearl producers out there. Clams, too, will form these shimmering clumps to trap irritants that enter their shells. In fact, a fisherman once found a 34-kilogram pearl inside a giant clam.

So, yeah, clams aren't just fascinating; they might also be precious. Plus, they actually play an important role in their environment. By sucking up particles to eat, they function like natural water filters, making marshes, lakes, and other habitats more livable. And, on top of that, they're delicious to eat. Not to mention, really fun to collect.