It’s safe to say that we have explored most of the land on our planet at this point.

But the oceans are a totally different story. We’ve probably covered less than 5% of what’s down there.

So it’s not too surprising that scientists and explorers keep finding things in the ocean that don’t seem to follow the usual rules of biology. For example, a single-celled organism called a xenophyophore. See, even though xenophyophores are single-celled, they’re usually about 10 centimeters in diameter.

And the largest ones can grow to about 20 centimeters. They’re a type of protist, meaning that their cells have a nucleus, but they’re not a plant, animal, or fungus. Xenophyophores are really hard to study, because they are fragile and no one’s been able to grow them in a laboratory, so we don’t really know a lot about them.

Except that they are super weird. In 1883, English paleontologist Henry Bowman Brady found a xenophyophore among a bunch of other deep ocean stuff and classified it into a family of protists called foraminifera. Foraminifera get their own family because they’re a lot different from other single-celled protists, like algae: they produce and build protective shells.

Most species of foraminifera make their shells out of calcite or limestone. The xenophyophore had a shell, so Brady thought it might have been an older, gigantic form of these tiny shell-makers. And for a single cell, they really are enormous.

If you wanted to fill an average-sized xenophyophore with average-sized human cells, you’d need more than 100 billion human cells! So how on earth does a cell that massive even exist? Well, xenophyophores cheat a little bit, because they have lots of nuclei within one giant cell.

The nucleus is the part of a cell that tells it what to be, what to do, and where to go. Most cells have just one or two nuclei, which means they are limited to a specific role. Like, you have liver cells in your liver, and kidney cells in your kidneys.

You need different types to do different things. But xenophyophores have thousands of nuclei, which means that one cell can do all of the things it needs to survive. A xenophyophore’s life is pretty simple.

It’s just find a good spot on the sand or rocks of the ocean floor and wait. Unlike most foraminifera, xenophyophores don’t actually produce their own hard shells. Instead, they’re scavengers.

They chill on the sand waiting for bits of dirt, dead animals, rocks, and minerals to fall on or near them. Then, they just stick everything together using a sort of, like ... like, poop cement. So basically, they live their lives coated in the skins of dead animals mixed with their own poop.

Sounds nice. But this is not the end of the weirdness—oh, no. They’re also … sometimes radioactive?

Researchers have found that some species of xenophyophores, depending on where they are found, have unusually high levels of elements like uranium and radon in their shells. No one really knows exactly why, but it’s thought that they might be a sort of sponge when it comes to soaking up metals. That might also explain the equally unusual levels of mercury and barium sulfate in their shells.

But scientists are still pretty confused about how and why they absorb all this stuff. They are just another one of those strange, mysterious things living in the ocean. In houses made of poop.

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