"Strange is this animal ... because it resembles a bear in miniature." *
Kingdom: Animalia
Phylum: Tardigrada
Class: Heterotardigrada
Order: Echiniscoidea
Family: Echiniscidae
Genus: Echiniscis
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Overview
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There are lots of very common animals. We don't know everything about all of them.
Water bears are simultaneously some of the most common and some of the most mysterious animals in the world. Their phylum is reserved for them alone, yet they live almost everywhere on Earth — if you've seen a pile of leaves, you've seen the habitat of the water bear. Additionally, if you've inspected a clump of ocean sediment, or managed to tunnel five meters into a sheet of Himalayan ice, you might have happened across one there as well.
All 800-odd species of water bear are extremely small — small enough to disallow observation with the naked eye. Interestingly enough, they're built like larger creatures. They move smoothly and have eyes, skin and muscles. While I explained above that water bears can inhabit just about any place (a matter of how they do this is a topic I'll get into shortly), their typical homes are mild places like moss cushions and freshwater lakes. They eat moss leaves and algae, utilizing for the task sharp objects in their mouths called stylets (presumably, synonymous with pens).
Female water bears outnumber males and are slightly larger. They lay their eggs in shed exoskeletons. Several molts precede adulthood in both sexes.
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What do they look like?
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The water bear is not a majestic creature. In images that show detail — specifically, those created via scanning electron microscope — you might liken it to an insectile version of the mammalian bear. Its body is largely shapeless; extending from it are eight thick legs tipped with comparatively large "claws." It has transluscent skin, and that, combined with the reddish, grayish or greenish color of its internal organs, might make it look like a gummi bear under the correct light. Few images exist because of the difficulty in getting the animals in focus under standard microscopes; they stand on legs, and are consequently somewhat taller than other microorganisms. Thus it is difficult to get a focus on them in their entirety. Pressing them in slides causes them to perish and disintegrate almost instantly; it goes without saying that this hinders any procedures to get a good look at them as well. Not to mention that it's a bit inhumane.
A somewhat detailed image can be found at http://www.abc.net.au/science/news/img/tardy.jpg. I think it's from an SEM.
Here's a link, courtesy of BlueDragon, containing an animated pic: http://www.microscopy-uk.org.uk/mag/artmay99/dwbear.html.
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So why are they so special?
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Water bears are remarkable because of the "abiotic state" to which they revert when conditions turn bad. In a nutshell, the antibiotic state is similar to a state of living death: when absent from the moist conditions of its ideal habitat, the water bear will dry up and, in effect, cease biological activity. It exits this state when conditions become favorable again, whereupon it rehydrates and continues living as though nothing had happened. Tests reveal that the antibiotic state renders the water bear resistant to things like solvents, storage in liquid nitrogen, radiation, and absurdly high temperatures (up to almost 300 degrees Centigrade). One source claims that a water bear in an antibiotic state might be able to survive in outer space. Specimens established to have been in the state for well over a century have been reanimated and continued life, unaffected and oblivious.
So, to be fair, if you did tunnel into five meters of Himalayan ice and find a water bear, it would probably be antibiotic.
Lab instructions for reanimating a water bear are available at http://homepages.culver.edu/faculty/jcoelho/biol206/TARDGRAD.HTM.
"Water bear" is also a band.
* Joh. August Ephraim Goeze: Herrn Karl Bonnets Abhandlungen aus der Insektologie. Cited in source number one.
Sources.
- http://www.microscopy-uk.org.uk/mag/artjun00/mmbearp.html
- http://www.fcps.k12.va.us/StratfordLandingES/Moran%20Website/mpages/water_bear.htm
- http://www.geocities.com/RainForest/6135/tardig.html
- http://homepages.culver.edu/faculty/jcoelho/biol206/TARDGRAD.HTM
- http://www.bartleby.com/61/69/T0046900.html