Tiny White Bug?

[pokerfish]

Bought a piece of rock today from LFS with mushrooms (first coral ever) and after Biff calmed me down when I saw a bristle worm (thanks again) I just saw the tiniest little white thing shoot from hole to hole...it isn't very long (like a worm) more like a very thin grain of rice...Is this bad? Its very small and quick and I will never be able to get a picture...

 

[Bifferwine]

It is probably an amphipod -- which is a good guy.

 

[AmberSunrise]

Probably a live feeder shrimp like a brine. I always get them on coral rocks because my lfs uses them to feed and they hide in the rocks.