The White-spotted Hermit Crab "Dardanus megistos" is not safe for a reef aquarium because it will eat tube worms, mollusks, and fish. It will also eat algae. In a community tank, however, it will keep the sand sifted with its constant search for food. It is best to keep just one specimen per tank, since it is aggressive towards other Hermit Crabs. It is believed that it may also snack on Aiptasia anemones, but how effective it is at eliminating these pest anemones has not yet been determined.
HTH.