Tardigrades are within the Superphylum Ecdysozoa and about 400 species make up the Tardigrada phylum. These 8-legged segmented bits of awesomeness live in water and are the some of the most extreme of all the extremophiles. Tardigrades are able to survive near absolute zero (-459F) all the way up to 304F.
Here is a short video from National Geographic:
Tardigrades are being utilized in research as a model system to examine development driving the evolution of morphology. Follow this link to the Goldstein lab at UNC-Chapel Hill.