The above answers are correct. Its not a shrimp at all. Its a stomatopod. Seeing as how is is out in the open enough for you to take pics, I would consider relocating him now while you can. He should be fairly easy to suction out with a hose like the one you do water changes with. Suck him into a bucket, and take him to a LFS, set up a little nano tank for him, or find someone to give him a home.
One of three things will eventually happen if you dont.
1) he will eat all of your inverts. crabs, snails, everything.
2) he will eat all of your smaller, slower swimming fish
3) he will eat everything in your tank, and move your corals around to his liking.