sponges/fish serial killers need capture

[sponge brain]

Please help identify/capture fish & sponge serial killer
I have already lost two small fish 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
I would appreciate your input !!!!

 

[thomas712]

Hmmm. Wonder if this could be the infamous gorilla crab. I'll call Sheriff Taylor and he'll probably send Barny out for a look see.
Buy some club soda and soak your rock in it, those bad boys will bail out.
Set up a trap with some meaty food, and get em out of there.
Thomas

 

[chinnyr]

Here's what I did to catch mine.Clean out a 20oz.plastic soda bottle.Cut it in half about 2 inches from the top.Invert the top piece into the bottom so it looks like a funnel.Put some bait inside.Place it near one of the crab's hideouts at night when the tank lights are out.You should catch him in no time if he is a foracious of an eater as you say.I caught mine in about 10 minutes.Use a flashlight when the lights are out to see them.They are very active at night.I have one or two small ones that are a little big more red than brown,and they really don't bother anything.Good luck!