Water Bears — Tardigrades

Water Bears — Tardigrades— an animal built on only a few hundred cells.

Tardigrades are polyextremophiles.  (An extremophile is an organism that can thrive in a physically or geochemically extreme condition, one that would be detrimental to most life on Earth.)

• Tardigrades can withstand temperatures from just above absolute zero to well above the boiling point of water,
• pressures about 6 times stronger than pressures found in the deepest ocean trenches,
• ionizing radiation at doses hundreds of times higher than would kill a person,
• and the vacuum of outer space.

They can go without food or water for nearly 120 years, drying out to the point where they are 3% or less water, only to rehydrate, forage, and reproduce.  [Wikipedia]
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IMAGES
Tardigr E granul — 700x 
This water bear lives in moss and awakens, as it were, when the moss gets wet. It feeds on moss by sucking the cells off. If the moss becomes dry, the water bear will sense this and encapsulate itself.  If necessary, it can wait for years until the next rain.

Tardigr Pm kenianus — 300x 
This tardigrade, first discovered in Africa, feeds on bacteria and protozoans.

Both images courtesy of Oliver Meckes