Crab! Help Id

[Reesy1989]

Hello Everyone!
 
Happy New Year!
 
I had decided to set my marine tank back up. Everything has been going great. The new LR I bought also had some hitch-hikers, which was great. However I'm now thinking its not as great as I once thought.
 
There is a crab, which has been very shy whenever I've approached the tank and has been difficult to get pictures of. However since adding my CUC it has been out a lot more.
 
I've attached some pictures as it has black claws which I know is generally not a good sign, I also found it circling an upside down snail this morning.
 
Any help getting this ID'd would be appreciated!

 

[Chad]

There are hundreds of species of small crab so getting a specific ID is often impossible. 
 
For many reef keepers all crabs are bad. I don't follow this thinking but if you want to be on the safe side this guy would be better off in the sump if you have one or in its own tank. 
 
One main way to decide is to look carefully at the claws. If they are spoon shaped like an emerald crab's then the crab is likely going to be okay. Like the picture from Google below. 
 

 
If they are scissor-like or crushing tools then don't keep it around. 
 
Here's a good resource I use for crab hitchhikers. Again, not a complete resource (though it links to a pretty complete one) but it should give you a nice guide. 
http/chucksaddiction.thefishestate.net/hitchcrabs.html