I just discovered my sally lightfoot crab dead. Something had killed and started to eat it. I;m confused, because i dn't have anything in my tank that should eat the crab. What might have done this? LIVESTOCK INCLUDES: yellow tang, copperband butterfly, firefish, blue damsel, tomato clown, percula clown, black spined urchin, bubble anemone, and various snails and blue leg hermits.