Fishing for crab techniques

[Scavenger]

Last week just before lights out, I was watching my mushroom rock when I noticed a claw extend from a hole in the rock. Well, it looks like I got a hitchhiker crab. The claw was purple with black tips. From my research, I beleive it is from the Xanthid family and they are generally destructive in a reef tank. I was hoping to get some suggestions on how to catch this little guy so I can get a possitive ID on him and deside whether or not he has a home in my tank. He has shown his claw a few times during the week but does not seem to move from his hole. I have flashlighted the tank at night but have not seen him come out yet.

While on the hitchhiker subject, I also have what I beleive to be a brittlestar or similar body shaped star living in another rock, he too won't come out. he is very small and the legs are banded dark green/grey and white. Any cause for concern here?

Gee I love my new hobby, it's like being Dr Dolittle, Sherlock Holmes and Grounds Keeper Willie all at the same time!