This Martian would need to live under ground to escape from the extreme conditions on the surface. It would need to extract moisture from the permafrost trapped in the rocks beneath the surface. It would only be the size of a small Earthworm but of course be a Martianworm.

It would also be able to extract enough oxygen from the water in the rocks to breathe. Like a fish can in water, except the lower atmospheric pressure on Mars would allow the gases to escape quicker once they were chopped up by the Martianworm.