Hey,
I just bought a emerald crab today. Now I know you should check everything you buy, I usualy do but this time I just gave a quick check. Needless to say, when I got home and put him in my tank, I noticed that he has 4 legs on one side... and 1 on the other. Now how long can this guy survive like this? How hardy are emeral crabs?
I would bring him back to where you got him and ask for a normal one. If its a decent Lfs or seller they should have no problems exchanging another one.
I had an emerald that lost 3 legs on one side, he lasted about 3 or 4 days
^^^ pretty much what I think
I have a red emerald where the same thing happened, I got him home and he was missing a claw and another regular leg on one side. He is doing fine so far, I have had him about a month or so. His name is Lefty. I don't have any fish that bother him though.