Have you tried taking out just the rock it's taking refuge in and doing an iodine dip or a scalding hot water dip? I had one in my tank and the hot water worked.
I'm not going to lie to you, I just couldn't bring myself to put the rock back into my tank, out of fear it had friends I might have missed...call it irrational but anything with more than ten legs and can move with lightning speed give me the major heebie-jeebies.
Good luck!