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- 0.5 millimeter
What is a tardigrade?
Tardigrades are microscopic eight-legged animals that have been to outer space and would likely survive the apocalypse. Bonus: They look like adorable 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, hence their nickname, moss piglet.
Despite looking squishy, 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 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 or above boiling, at pressures six times that of the ocean’s deepest trenches, and in the vacuum of space.
Their resiliency 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 their heads and limbs, roll up into a little ball, and become dormant. When conditions improve, they unfurl themselves and go about their business.
Mating and reproduction
Naturally, tardigrades have unusual mating habits, too. Depending on the species, the animals may reproduce asexually 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 state.
DID YOU KNOW
Tardigrades have been on earth about 600 million years, preceding the dinosaurs by about 400 million years.
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.