Water bears (Tardigrada)
The water bears are a very strange type of animals caracterized by being invertrebates, segmented and microscopic (0.5 mm average).
The tardigrada were described at first by Johann August Ephraim Goeze in 1773, who determined them as water bears. This name is refered to how the tardigrada walks, similar to the bears walk. After, the term tardigrada (that means slow pace) was given because of the lowness of this animal.
These animals have unique characteristics in the animal kingdom like surviving in the space, with so high atmotsferic pressure and temperature under the -200°C and they also can live 10 years without water and they are not affected by the ionic radiation.
Most tardigrada are terrestrial and live in the layer of water that covers mooses, lichens and ferns, but they can also live in ocean water or freshwater, living in all parts of the world.
The water bears are of an oval or elongated form and feed sucking vegetal liquids or animals and they have eukaryotic cells. There are more than 1000 species of tardigrades known.
The tardigrada are formed by 1000 cells and some species are eutelic (they keep constant the number of cells during development). Nevertheless, other scientist say the number of cells is 40000.
The Tardigrades feed of bacteria, cryptograms, rotifers, nematodes and other microscopic invertebrates.
Normally the tardigrades sip their cells, but in another ocations, they eat complete organisms.
If you want to know more about this very strange animal, see this video.
