Could any known, living organisms on Earth survive on Mars? No life has been discovered outside of Earth (yet?), but do we know if anything that would be considered "living" on Earth could conquer Mars? (or maybe Venus?)

With the Mars One project on the way, I was wondering if it was possible to transplant some of Earth's life to Mars, and if something could survive there (naturally).

Many kinds of life are based on air and sun. Animals have to breathe oxygen, plants need the sun, and both need water. But there are many other kinds of life on Earth, like:


Very deep seawater life that lives under high pressure and without sunlight,
extremophile organisms that live in very hot water,
weird "arsenic life" which was debunked as being fully arsenic-based, but turned out to be something different...


Have there been any theories or studies about unusual forms of life on Earth that might survive on Mars?
The most likely candidate would be the Tardigrade. These little guys handle vacuum and radiation just fine. So long as water is provided, according to tests done in LEO the Tardigrade would survive on Mars. Even if they do dehydrate, they spring back to life once water is provided again.