Xanthidae Crab! (I think)
 

Found one mining tunnels into one of my live rocks. Never would have seen it had I not decided to survey my tank one night with my trusty Mag-lite. Needless to say I'd like it gone but I don't know how to fish it out. Suggestions?

I've had a couple of those. They can be harmless for a while and then suddenly turn on ya and start wrecking house.

Try burying a cup with food into the sand; he get's lured in and can't climb out. It usually works. With my xanthids I had to eventually stake them out, chase them into a loose piece of live rock and drag the rock out for a fist fist with some crabs.

I'll give the cup a try. But as for taking the rock out I don't think it's possible without disrupting my aquascaping. Thanks for your suggestion.

I've been having luck catching crabs in my live rock with a product called the x-terminator. I bought it at www.mops.ca

I just put some bait in, mysis shrimp, and put in near the rock when the lights go out. Each time I've used it has caught a crab.

crab
 

i'll tag along on this one i think i have one in my 55 gal so are they coral killers or fish eaters!

I caught 8 of these crabs in my SMALL reef aquarium!
Searched the web high and low on how to catch them and the best method I found was using a tall glass cup leaning on the rockwork with bait in the bottom.
Crab falls in after the bait and can't climb out as there is nothing for him to grip on the glass!
It worked great and cost me nothing :-)
Good luck, it took me a couple of weeks to get them.
Lori