ID Please

[beefORchicken]

So there's a strange creature that has made holes in some rock and a worm like arm pokes out like a 'whack-a-mole'. I've never seen it before and i think there's only one animal since only one arm pokes out at a time. Any ideas of what it is?

This picture shows the holes in the rock, the highlighted area is about the size of a toonie