Indestructible Tardigrades

At less than 0.05 inches long, most tardigrades are too small to be seen (or at least differentiated from the common dust speck) without a microscope. However, no matter where you live, these tiny animals are probably close by if you’re willing to look for them.

A tardigrade is a teensy aquatic animal belonging to the phylum Tardigrada. Tardigrada is part of the larger clade Panarthropoda along with phyla Onychophora and Arthropoda – that said, I’m kind of cheating talking about tardigrades on an arthropod blog since they aren’t arthropods themselves. Nevertheless, I think tardigrades are pretty stinkin’ cool, and it’s kind of unclear where they actually belong in terms of animal phylogeny anyway. So, I’m going to say they’re close enough to being arthropods, and we’re gonna talk about ’em.

Tardigrades are often referred to as “water bears,” which I guess makes sense as long as you ignore the fact that they have eight legs. And have no ears or fur. And have that weird tubey thing in the middle of what one would assume to be their face.

A tardigrade illustration uploaded to Flickr by Rebekah Smith

Honestly, they look a lot more like legged micro-croissants than any animal I’ve seen. But “water bear” is a cute name, so I guess we’ll stick with that for now.

Water bears like to live in moist environments, preferably in moss (earning them the additional nickname “moss piglet”). Commonly herbivorous (but occasionally cannibalistic), tardigrades use that funky tube or stylet to puncture plant cell walls and drink up the cytoplasm inside. They also hunt down and suck up the innards of harmful bacteria.

One of the reasons I find water bears so fascinating is that they are virtually indestructible – and keep in mind, this is an animal whose skin is thin enough to see through under a microscope. While these itty-bitty animals prefer the comfy microclimate of a moss bed, they are found everywhere: on the highest mountain peaks, in the deepest depths of the ocean, on every continent and in every biome. However, not all environments are equally suitable for a tardigrade to live in, especially habitats devoid of water. When water runs low, the tardigrade undergoes a process called cryptobiosis in which it basically reversibly dies. It’s like if you ran out of food and fell into a coma but woke up again the instant someone walked in with the groceries.

The specific form of cryptobiosis most tardigrades undergo is called anhydrobiosis, in which the tardigrade expels all the water from its body and folds up like an accordion into a special state called a tun. Water bears could teach us all a lesson in patience: a tardigrade tun will spring back to life as soon as it comes in contact with water again, but it can wait in this state for decades. In fact, tardigrades were once revived from a moss sample in a museum that was 100 years old!

A tardigrade photographed by Phillipe Garcelon on Flickr. The two tiny dots on its head are its eyes.

Even in harsh environments, tuns are incredibly resistant: they have been known to survive extremely hot and cold temperatures, obscene levels of radiation, and even outer space. Let me rephrase that last bit: someone thought “hey, let’s launch some tardigrades into the cold emptiness of space and see if they survive.” And they did! Dehydrated water bears can float around completely exposed in the vacuum of space and live to tell the tale. And not just for a few hours, either: those tardigrade tuns were left in orbit for ten days, and most went on to live happy, healthy lives after being rehydrated.

Alas, even the mighty water bear has its limits: tardigrades are unable to survive the human digestive system, or being fired from a gun. No, not being fired at with a gun – being fired out of a gun.

Scientist 1: Wow, tardigrades can survive in the vacuum of space, amazing! There really is no limit to their resiliency.

Scientist 2: Or is there?

Scientist 1: How could there be? We’ve frozen them, cooked them, bombarded them with radiation… what else could we possibly subject them to?

Scientists 2: Have you ever seen a human cannonball act?

So, to sum up today’s post: there are probably some tiny, nigh-indestructible animals called water bears in your vicinity, and scientists have way too much time on their hands.

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