The critters, which average .5 mm long, were discovered in 1773 and are nick-named for their resemblance to bears, though their taxonomic name, Tardigrada, translates to "slow stepper."
Tardigrades thrive in moss, lichen, lakeshores, and other moist environments though they are also found in extreme environments like deserts, deep ocean trenches, and in high tree tops. Water bears have a full alimentary canal and digestive system. Mouth parts and a sucking pharynx (see Scanning Electron Microscope (SEM) image below)
lead to an esophagus, stomach, intestine and anus. They have well-developed muscles and a single gonad. Tardigrades have a dorsal brain atop a paired ventral nervous system.
Water bears can go without food or water for more than ten years, drying out to the point where they are 3% or less water in a process known as cryptobiosis. It astounds me to think of something with a brain and nervous system being able to curl up into a ball for years, lose most of their water content, and still survive. They can then rehydrate and just carry on normal lives.
Water bears have been around since the Cambrian period, surviving major extinctions at the end of the Paleozoic and Mesozoic time periods. There are over 1000 species of tardigrades, most with 8 claws or disks:
Bob Goldstein from the U of North Carolina, who has done SEMinal (pun intended) research on the little beasts, says of water bears, “There’s one thing that we know of, which is some animals that survive drying make a sugar called trehalose.” He continued, “And trehalose sort of replaces water as they dry down, so it will make glassy surfaces where normally water would be sitting. That probably helps prevent a lot of the damage that normally occurs when you dry something down or when you rehydrate it.” Not all of the >1,000 species of water bears produce this sugar though, he says, so there must be some other mechanism involved.
Neal DeGrasse Tyson featured tardigrades this spring on Cosmos. Are they old friends of yours or new acquaintances?
Better late to the tardi(grade) than never,
Guess what is in these two false-colored SEM images:
SEM IMAGE 1
And for comparison, the same thing without magnification:
Aren't fractal veggies cool?
And one more in black and white:
SEM IMAGE 3
Those mathematicians can be vicious: