Bristleworms...Ugh

Most bristleworms are harmless (except if you touch them, don't do that!), like said by others, but there are a few types that can be destructive. Chances are that yours are fine. Here's an article about some of the bad ones and another site with some good ID's.

Polychaete Annelid Identification, or “You Can Always Tell A Bristle Worm… by Ronald L. Shimek, Ph.D. - Reefkeeping.com
Worm Hitch Hikers

There's also a lot of info in the ID This forum here on 3reef, check out the stickies.