bill109,
They are generally peaceful and are
GREAT scavengers/cleaners. However an infestation can get pretty ugly. I'd leave him unless you notice him start to damage your corals (unlikely I'm told).
My husband and I have at least a dozen in different areas of our tank and they keep to themselves pretty much. In our 23-gal tank, it's comfortable. However I have seen infested rock and not only is it disgusting, but that can pose a threat to the other life in your tank.
I know of two ways you can catch/eliminate them:
1. Take out the rock it lives in and dry it out. That'll kill it - but this way can be a pain in the butt especially since I've noticed they like to live close to the ocean floor, aka your base rocks lol.
2. I've heard you can take the cut end of a pantyhose, stick a bit of fish inside it, tie a knot in the open end, and set this somewhere on the bottom of your tank. They will burrow into the pantyhose to get to the fish, but won't be able to burrow back out.
Careful not to touch them - it's like getting stuck by a cactus.
Again unless you have a severe infestation of them, I'd leave them be. If you've got one, you've likely got several more. They're nocturnal and most often come out at night, or at feeding. They're part of your cleaning crew and a good thing to have around
Kara