Need help getting a small crab out of my saltwater tank!?

ok so i have like 2 or 3 of these small maybe 1/2 to 1 inch brown hairy crabs in my tank. I dont know what they are called they kinda looked like a horilla crab but who knows. (any thoughts by the way?) Any ways i have been told it looks like some crab that will eat fish which is a no no lol.
The only thing that contradicts what i have been told is that when i see him he is not munching on my frogspawn or mushrooms. He is nipping at the live rock. I have peppermint shrimp and a royal gramma in my tank and they are both fine.
Any ideas what it is and a good way to get it out of my tank with out having to take apart all my live rock?
Answers:
Here is a website that has traps: http://www.drsfostersmith.com/product/na... look at the pes-trap and the x-terminator!!

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get a small fish net

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Do you a net you could use or perhaps some rubber gloves?

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Crabs are mostly omnivores.
For picture ID of various hitchhiking crabs
http://home2.pacific.net.ph/~sweetyummy4...
http://home2.pacific.net.ph/%7esweetyumm...
Removal when you see them:
The first paragraph of this next link discusses removing crabs, and others from live rock before you put NEW live rock into your tank 'use a spatula to either whack them or flip them away from the rock (after previous steps)"
http://www.simplifiedreefkeeping.com/faq...
Since, though, you are in a tank, perhaps you can whack them smartly with something when you see them to stun/disable, then pick them up with tank tongs or net. Or, more cunningly, use one of those plastic half-tubes which small creatures can go into to hide under and feel safe but are see-through to outside observers (don't know if will be okay in salt-water), if they like to hide, and hide there, you can catch them live with nets.

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maybe they are just emerald crabs, which are fine in your tank. but here's a good way to get them out if you dont want them, take hand, stick in tank, pinch fingers on crab, pull crab out of water. simple, and free.

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let the crab pinch you then pull it out