Emerald crab missing 6 legs

[shane1234civic]

So i have had my tank up and running for 3 or 4 months now. I have 6 emeralds 1 died a months ago. I came home and one of them who was missing one claw is now missing both and 4 legs. Any Idea what could of happend. The tank i have a 72 bow front with 4 or 5 emeralds 2 pepermant shrimp and a fire red. And just a few small community fish. Im thinking maybe i got a mantis shrimo in my live rock. But ive never seen one in there If so i have no idea how to catch it. I dont think it could have moted and lost that many limbs or maybe another emerald crab could have fought him. I just added two crabs the other day. I dont know wny helo would be great.
Thanks
Shane

 

[Koshmar]

I think it would be the other crabs. If you had a mantis it probably would have outright killed the crab. I fed one of my mantises an emerald a while ago and it simply killed the little guy instead of eating it. Since the emerald is so defenseless I see no reason why a mantis wouldn't finish the job and get a free meal. They target the claws and once those are all gone they pull the prey into their burrow. I'm not ruling a mantis out but IMO it would have taken the rest of the crab instead of letting it live in such a weakened state.