Wondernose: What animal has no head and no legs, yet weighs a quarter of a ton?

by Rebecca Martin | Aug 1, 2022 | 0 comments

Giant clam, coral, underwater animals
Giant clam. Photo © Dreamstime.com.

Mind you, Wondernose, not all the animals of this kind weigh a quarter of a ton. They can vary in size from a fraction of an inch to four feet across.

But how, you wonder, will such an animal get around if it has no legs? The answer is that it does have a foot. Just one single foot. Obviously this animal can’t run fast, but it can move slowly from place to place.

No, the answer is not a snail. I doubt if you’d ever see a snail that weighs a quarter of a ton.

Our mystery animal also uses its foot for burrowing in mud or sand. Its favorite habitat, you see, is at the bottom of the ocean—though mostly in shallower water. You will frequently find these animals on coral reefs.

Being an underwater creature, our animal has no lungs. It breathes by means of gills. Interestingly enough, the gills serve a dual purpose. Not only do they take oxygen from the water, but they also collect the tiny food particles upon which our animal lives. Yes, this headless, legless, tailless animal has a stomach for digesting food!

They have quite a plumbing system. Some species have two siphons, one for drawing in water and the other for sending it back out after the gills have done their job. So our mystery animal is constantly taking in water, filtering it, and pumping it out.

How do the food particles get from the gills to the stomach? Through the mouth! So you’re surprised that a headless animal has a mouth, Wondernose? Well, I guess this animal is full of surprises.

The food is passed from the gills to the mouth by means of cilia. What are cilia? They could be likened to tiny hairs. The cilia are busily waving to and fro, directing food to the mouth. It sounds complicated, doesn’t it, Wondernose?

Our mystery animal has a soft, squishy body. But it is protected by a hard outer shell that comes in two parts and can be opened and shut. The two parts are called valves. A ligament joins the two valves together and…

Yes, Wondernose! Our mystery animal is indeed a clam. Now, if it’s a clam that can weigh up to a quarter of a ton, what do you think is the other part of the name? That’s right, this is the giant clam. I have never seen one, but I think if you were walking along the seashore and came upon such an abandoned shell, it would be an impressive sight. People like to use giant clamshells for decorative purposes in their gardens. Wouldn’t a giant clamshell make a nice bird bath? Since the opening edges are scalloped or corrugated, it makes them all the more decorative. On a live clam, these corrugated edges fit tightly together when closed.

Right inside the clamshell’s opening are two fleshy flaps called the mantle. A giant clam’s mantle is usually a vivid blue or purple color.

Ranged along the edges of the mantle is a series of eyes. Hmmm. No head, but eyes and a mouth! A strange animal indeed.

Now you wonder what the shells are made of, Wondernose? The short answer is chalk. Or we could use the fancy name of calcium carbonate.

Do baby clams have shells? Not at first. Newly hatched from a tiny egg, a baby clam is called a larva, or a veliger, if you like that name better. As these little free-swimming creatures develop, the mantle begins to secrete the chalky substance that produces the shell. Wouldn’t it be fascinating to watch a clam shell being made?

The so-called “clams” that you and I find in our streams are actually fresh-water mussels. There are also salt-water mussels, and they’re so numerous that, on some coasts, there are millions of them.

A lot of people like to eat mussels and clams—not the shells, obviously, but the soft bodies inside. What do you think,
Wondernose? Would you like to try some clam chowder?

A clam’s foot has still another purpose that I’d forgotten to mention. Besides being used to move about, it also serves as an anchor. That sounds contradictory, doesn’t it? But you see, the foot secretes sticky threads called the byssus, which anchor it to whatever surface is handy. These threads have sometimes been called the clam’s “beard.”

So there you have it—an animal with no head, yet it possesses eyes, mouth, and a beard!

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