They appear to be very dark, overly large worms - perhaps a handspan in length and half as thick as a finger. That and their matt, dull skin marks them as something other than a typical earthworm.
What do you mean, the little wriggly ones you throw at fish or the big rock ones that squish people?
Six months of hunting, six months of research and paying coin to scholars and sages, and now that we have the legendary wand of Geohadris the Stone King, it only summons stupid boulderkin? I am outraged beyond imagination!
Mapmaker's bane, a few of these can ruin a decade of cartography!
Every now and again, the region encounters a dense blue fog. Every now and again, things disappear into the fog never to be seen again and things appear out of it from other places or world. It seems the fog is the material form of some minor diety charged with moving things around the universe to balance cosmic forces.