We had the same problem with our bristle worm. Shame too because he was so cool looking, but not worth my favorite shrooms
! My hubby caught the bugger in the act and yanked him out by scooping him up with a skewer, if I'm not mistaken. He said he had to pull him off of the shroom he had such a hold on it. The shroom has a small scar where the bristle got him, but has otherwise flourished.
If he's *in* the rock maybe you can pull the rock and squirt the hole with fresh water. The shrooms
wouldn't be out of the water very long and the worm should wither from the fresh water. The rocks I've pulled have never had anything more than coraline and spaghetti worms on them so I just pulled the rock, hit it with FW
(over a bowl) and then put the rock back into the tank. Just keep the shrooms
out of the fresh water.
I was going to keep mine in my fuge, but now that my QT
has had ich I'm not interested in moving any of the old inhabitants (couple of crabs, worms and snails) to my fuge!
Good luck. I feel your pain!