I had one of these once. Found it by dumb luck.
I was breaking up a rock with a hammer and chisel. When I picked up the rock to turn it over.
This thing came "oozing" out of the rock. It freaked me out pretty bad, but I managed to hold on to the rock.
It seemed like forever, waiting for it to come all the way out, but it evidentally didn't like what I was doing and chose to leave the rock on its own. Not saying it will work for you, but it might.
Also, you could try mixing some saltwater to 1.031 or higher and put the rock in there.
This works for pest crabs and mantis, but I am not sure about worms.
Also, thanks for reminding me, I think my Eunicid-cicle is still in my freezer!