Help - Mantis Shrimp or Pistol Shrimp

[j83]

The other day I bought a few Emerald crabs and whenever one gets near a certain hole in the rock, I can see and hear a tiny 'shrimp' snap at the crab. The hole that this thing is living in is tiny and I have not added any new live rock in well over 18 months... From what I can see, it's 'snapper/pincher,' for lack of a better term, is about the size of a grain of rice.

I am trying to figure out if it is a Mantis Shrimp or just a Pistol Shrimp. Does anyone have any experience with either of these creatures? From what I have read, mantis grow to be somewhat larger (ie. 3-4 inches) than pistol shrimp who are smaller in size. With the rock in the tank being older, I would think that what ever is living in it would be past it's juvenile stage and closer to full size? Is there such thing as a mini mantis?

Thoughts? Thanks in advance!