What kind of crab?

[rayt]

I have a crab that arrived with live rock that is about the size of a quarter, light tan/white body and claws, tan and brown striped legs, a brown pattern on the top of the shell and the actual pincers are black. It is nocturnal.

 

[MedicineMan1]

Actual crab ID by us mortals is nearly impossible. I had one that answered that description that had an enormous appetite for xenia.

General rule of thumb on crabs is that they are almost always carnivorous, given the opportunity. I'd suggest sending it to your sump.