Is this a Mantis Shrimp?

[newreefer_59]

Have had a 150 gallon tank up and running for 6 months now, and finally spotted and photographed a critter that has been in the tank from day 1, I believe. We think it is a type of shrimp (Mantis Shrimp?) that came with my live rock. It is about 2 inches long and we caught him making a clicking noise on my new SPS Monti coral. This, I am sure, explains why the 10 little crabs I got about a month ago all dissappeared within a week, while most of the snails are still alive and well. My smaller cleaner shrimp stays high in my tank corner and rarely ventures down. Is anyone familiar with this shrimp and is it going to be a problem? Pics are not great as he is very quick and does not like his picture taken. Appreciate any help