A member of the relativaly unknown invertebrate phylum of Tardigrada and known colloquially as "Water Bears", Discovered in 1773 with over 800 species described since. The largest species is barely 1mm. Their nick-name arose from the bear-like pawing motion as they travel over sand grains, lichen, or pieces of plant material. These little "bears" live in marine or freshwater environments. I found this in a water sample from Assawoman Bay, a saline body of water near Ocean City, Maryland.
For a more extensive description of the phylum go to http://www.biodiversityexplorer.org/metazoa/tardigrades/index.htm