Anemone crab missing claw?

[Reefer302]

I just noticed today that My anemone crab has lost a claw Idk what could Be the cause the only inhabitants of my tank are quite peaceful a cleaner shrimp and a mandarin dragonet.
Also will the arm grow back or not?

 

[Chuk]

They can come back when they molt. It may take 2or 3 to fully return. It will be a little bigger each time.