to adress several glaring errors:
1. if you own a reef tank then be now you should be very familiar with that LITTLE creature, an amphipod, they chew on algae and ditritus, and generally are a good sign in the tank, unless you see tons of them in the open (thats a bail out)
2 if it were a mantis, and it isn't, how much damage could it do being that it's hardly larger than the dashed lines > ---- < ?
3. mantis shrimp are very very very unlikely to damage coral, they'll eat fish that are less than half their size or pound on small inverts. while some are capable of much greater feats, it's un typical. my mantis tank is also my frag propagation tank = ) i also have small hermits and astarea snails and an emeral crab, no losses yet.
4. amphipods don't move rocks, they scurry about them, even if it were a mantis, at that size what would it do? poor little fella