If one were to rate animals on two scales, how well known they are, and how well liked they are by those who know of them, tardigrades would be near the bottom of the first scale and near the top of the second. Very few non-biologists know what a tardegrade is, but people who know about them almost universally describe them as cool, cute and amazing. There is a very silly tardigrade song that makes the rounds of laboratory email lists. I count myself amoung those who have trouble not grinning when tardigrades are mentioned.
What is so cool about tardigrades? They can survive total dehydration, exposure to vacuum, radiation, freezing, extreme heat, conservative radio personalities, you name it. They can persist for a decade dried out with no signs of life, then just add water and they reanimate themselves. They are rolly and round and shaped kind of like six-legged teddy bears with two more legs growing out of their tails. This appearance has earned them the nickname ‘water bears.’
This afternoon I wanted to see if the hydra I am keeping in the lab would eat rotifers, because the Artemia I am giving them now are a bit too big for them, and rotifers a tiny. I found some in a puddle outside the institute, and in the same puddle, I found tardigrades. I had never knowingly seen a live tardigrade before, so I took a good long look at them under the microscope. These ones were well under a millimeter long, but I tried to get pictures.
They are small enough that really good photos would require a different microscope, but here are two.
This is a tardigrade from above. You can't really see how cute they are from above.
This is the shed skin of a tardigrade.
Just as snakes have to shed their stiff skins occasionally, many animals with exoskeletons molt that shell occasionally. All the arthropods (insects, spiders, crustaceans, crabs etc) will shed their skins, and so will tardigrades. Tardigrades are not arthropods, but are their closest realtive except for the velvet worms. This skin is head-end down. You can clearly see the six legs on the left side, and the two-legged tail at the top-left. I will try to get better pictures of a live critter tomorrow.