Tardigrades, also known as water bears, are microscopic animals that are pretty much indestructible. They can survive almost any hardship condition, including dehydration. When they lack water, they go dormant, for years if necessary, then rehydrate and begin their lives again. There are at least a thousand species of tardigrades, which make up their own phylum and aren't closely related to anything outside it. The picture above was taken with a scanning electron microscope, but tardigrades can be seen under much less magnification. This video shows a tardigrade living in a wet slide mount that acts like a tiny aquarium.
You can have one (or more) of your very own, because they exist pretty much everywhere. The Stanford Tardigrade Project has detailed instructions for finding tardigrades and making microscope slides. They use a Foldscope, but if you have any kind of microscope, you should be able to see your tardigrade pet. -via Metafilter
(Image credit: Goldstein lab - tardigrades)