help identify/capture fish & sponge serial killer

[sponge brain]

I have already lost two small fish(just disappeared, to never be seen again) and many sponges to these two big crabs that hitched a ride into my tank by hiding in live rock purchased two weeks ago. The crabs bodies are about the size of a half dollar or very close. They are brown/reddish in color and appear to be covered totally by short hairs. They are extremely fast and so far have been able to elude me every time I try to capture or eliminate them.
So, any suggestions on what they are and how I can eliminate them from the tank before anything else comes up missing or torn off the rock for food ? I mean they have forocious appetites !
I have to get them out quick.

 

[wallda]

Just an Idea and I am NOT an expert, but if you know what piece of liverock they are hiding in, you could remove if from the tank and put it in a pail of fresh water, I am sure they will come flying out!!!!! But remember it will harm everything else on the live rock. Just an idea, maybe others will post thier ideas.
Best of Luck
DMW

 

[broncofish]

Sounds like teddy bear crabs to me. GrumpyOldman had one in his tank.