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| A tardigrade seen by a special microscope |
What is a tardigrade?
Tardigrades are microscopic eight-legged animals that have been to outer space and would likely survive the apocalypse (the end of the world). Bonus: They look like adorable (lovable) miniature bears.
Around 1,300 species of tardigrades are found worldwide. Considered aquatic because they require a thin layer of water around their bodies to prevent dehydration, they’ve also been observed in all kinds of environments, from the deep sea to sand dunes. Freshwater mosses and lichens are their preferred habitat (place they live), therefore their nickname, moss piglet.
Despite looking squishy (very soft), tardigrades are covered in a tough cuticle, similar to the exoskeletons of grasshoppers, praying mantises, and other insects to which they are related. Like those insects, tardigrades have to shed their cuticles in order to grow. They have four to six claws on each foot, which helps them cling to plant matter, and a specialized mouthpart called a bucco pharyngeal apparatus, which allows them to suck nutrients from plants and microorganisms.
Tiny and tough
Tardigrades belong to an elite category of animals known as extremophiles, or critters (animals) that can survive environments that most others can't. For instance, tardigrades can go up to 30 years without food or water. They can also live at temperatures as cold as absolute zero (-273.15 degrees Celsius) or above boiling (100 degrees Celsius), at pressures six times that of the ocean’s deepest trenches, and in the vacuum of space.
Their resiliency (toughness) is in part due to a unique protein in their bodies called Dsup—short for "damage suppressor"—that protects their DNA from being harmed by things like ionizing radiation, which is present in soil, water, and vegetation.
Another amazing survival trick is cryptobiosis, a state of inactivity triggered by a dry environment. The micro-animals squeeze all the water out of their bodies, retract (pull in) their heads and limbs (legs), roll up into a little ball, and become dormant (having normal physical functions suspended or slowed down for a period of time; as if in a deep sleep). When conditions improve, they unfurl (unroll) themselves and go about their business (live normally).
Mating and reproduction
Naturally, tardigrades have unusual mating habits, too. Depending on the species, the animals may reproduce asexually (without having sex) or sexually. In some species, males deposit sperm inside the cuticle of a molting, egg-carrying female during an hour-long mating process. Some females shed their cuticle and then lay their eggs inside to be fertilized later by males.
Eggs take around 40 days to hatch, or as long as 90 days if they’ve been in a desiccated (very dry) state.
DID YOU KNOW
Tardigrades have been on earth about 600 million years, preceding the dinosaurs by about 400 million years.
—American Museum of Natural History
They were first described in 1773 by German pastor J.A.E. Goeze, who called them kleiner Wasserbär, or “little water bear."
The Israeli spacecraft Beresheet was carrying thousands of tardigrades when it crash-landed on the moon in April 2019. Later experiments show the animals likely died on impact.
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