There's a tiny white tube worm that I've seen a lot in the past. Spirobid worms? They're almost like little tiny feather dusters. Of course I'm assuming they aren't moving at all.
My money's on spirorbid worms. They're a good thing in my opinion but some folks can get infested with then. I've never had them go crazy but I just check out my tank and there are a lot under my rocks and in the overflow. I suppose they could get outta hand but so can just about everything else. I consider them a good thing and at very worse a neutral thing. I did a bit more poking about and the correct spelling is "spirorbid". Do a quick search and see if that's what you've got.