The tank is a little over a year old, I added a cleanup crew 3 months ago, and every snail in my tank is gone, 40 to be exact, most of the shells are piled up in a corner by my overflow, but none are damaged, just the flesh is missing, I've also lost 2 diamond gobies in the same time period. So I'm suspecting a mantis shrimp, I've looked late at night but never have seen one nor have I ever heard any clicking coming from my tank.