What The Hell Is That?

[MMAX]

Sorry I don't have picture of this but maybe someone will know what I'm talking about. I was looking at my live rock today and noticed something moving around on it. I looked closer and saw several tiny creatures crawling around, picking on algae and running in and out of the holes. They are almost transparent with what looks like a dark stripe down their backs. I would guess that they are some kind of shrimp. Has anyone ever seen these things before?