Here's one completely new to me:
Today's VSL:Science link calls attention to tardigrades (aka "water bears," for reasons apparent in the YouTube video above), which are barely visible invertebrates that live on mosses and lichens -- and through virtually anything.
Read more at VeryShortList.
Check out the "Tardigrades in Space" blog.
See lots of other tardigrade photos, which run from cute to a little scary.