They call it the Pistol Shrimp because it can snap its larger claw shut so fast that it causes an underwater shockwave to travel straight outward from the appendage. The resulting blast is powerful enough to kill small fish at a distance, and even stun much larger ones.

It is one of only a few species capable of producing Sonoluminescence - which is a sound so loud that it actually produces light - because the bubble created by this claw-shot, upon collapsing, briefly creates temperatures hotter than the sun.

http://en.wikipedia.org/wiki/Alpheidae

video of it in action
http://www.youtube.com/watch?v=eKPrGxB1Kzc