We might need a pic to be sure what it is. It could be a baby bristle worm. It could be a fire worm. It could be a syllid worm. The first one is good. The other two you might want to take out.
No camera. I do have a fire worm(I thought it was a bristle worm but I just looked up the pic and it looks like a little fire worm). This other thing is not a bristle worm but it is wicked tiny and I've only seen it once on the side of my tank.
Its also not a syllid worm. There are no legs either. It looked to be shaped like an earthworm, again very tiny and with the coloring I mentioned earlier.