Bad Crabs?

[hockey nut]

Well, I'm not sure . I thought after hermits and Emeralds you didn't want any other type of crab in your tank. I am missing a fish but then he is known for taking vacations before. I'm not too worried yet about the crab/crabs but was hopping to get some feed back on them first before I panic. They seem to have orange-ish body and limbs with black pintchers. I also see the odd fish with a nick or small chunk taken out of it's fins or sides. They heel quickly though. Not sure whats going on , but would rather be safe than sorry.