The hunter idea about those 3 areas sounds like a good possibility, but if it wasn't that I could see it being some kind of Worm(Wurm) monster( I think it was already mentioned in this topic) but in various other games and such i've seen monsters such as Desert Worms, Ice Worms, Jungle Worms, etc. I think it would be a cool monster to be able to kill, or putting together the hunter idea and mine...you lure it out of the ground with some kind of bait, then kill it for a reward or some kind of special drop used for something.