What is this in my LR?

[bamboo]

I posted this earlier but was not able to submit photos, I hope this time it works. It was hard to get a good shot of it because it is in a hole in the rock.

I noticed something in one of the holes in my live rock, I never seen it before, the last time I put new live rock in was two weeks ago, otherwise the rest of my rock has been in the tank for 6 months. I believe it is a crab but how could it have got into my tank? If it is a crab will it harm my tank? Right now I moved the rock it is in, into a bucket with my tank's water.

Thanks for your help

[Fluff]

Looks like you have a hitchhiker crab. He's got himself wedged in there good and what you are seeing is just his claw. If you have a red light, have a look after lights are out using the red light and see if he comes out.

[bamboo]

Thanks Fluff,

Is it a threat to my tank?

[Fluff]

That's hard to answer. From what I can see, it looks like a mythrax species of crab, simular/related to the emerald algae eating crabs. But, all crabs have the potential to be a threat as they grow. The thing to remember is, they are scavengers first and if the food source is there, they won't have to hunt. If there is no food available, they can and will take whatever they can. HTH

[bamboo]

I appreciate the help, I am trying to trap it in a glass so I can QT it and photo it for ID.

Thanks again