I was looking in the tank tonight when the lights were off and a shadow moving caught my eye on the polyp rock. So I grabbed the magnifying glass and some weird yellow-ish shrimpy type creature was running around the rock, inbetween the polyps. Then it shot into a small hole in the rock. Its only about an inch long.
Carried on sitting there watching this hole and then two little eyes popped out of the hole and started looking around. Just like a garden snails eyes and it would turn around and look in all directions then go back in. It then came back out, went down to the sand, picked some up with its claws and then took some back into its hole I first thought it was a pistol shrimp or something so was quite pleased, but then I thought that pistol shrimps have their claws out in front of them and their claws are pretty much straight. But I couldnt see claws on this one but eventually I noticed them down at it side, very similar to a Praying Mantis...uh-oh! So went on to google and typed in Mantis Shrimp and there is pictures of some that look very similar to this shrimp.

For all you that don't think what a Mantis Shrimp is or haven't seen what they are capable of when they reach a large size, watch this:

http://www.youtube.com/watch?v=Hkv_30niM_A


Yes the one in the video is about 10 times the size of this one but still, the hermit crabs in our tank aren't very big! If you listen on the video you can hear it whacking the crab, like a clicking noise. I remember my Dad saying quite a while ago that he was sitting there one night and could hear a weird clicking noise coming from inside the tank.
Not 100% sure that it is but it looks like a small one so may have to try and remove it soon. Its not the type on that video but looking through google images there are smaller ones that look very similar.