white curly worm on back of tank? Need ID

[whisk]

I have notice these very, very small worm like things on the back wall of my tank. I would say there is about 20 of them back there. They are a little larger than the size of a pinhead, and they are curled up in a U shape. Here are some pics, sorry they aren't the best, my camera has crappy lens. There was one on a rock up close to the tank as well. I have seen them before on this site but I cant find the old post. Can someone tell me what they are and if they are harmless or not? thanks!!!

 

[cranberry]

It's a Spirorbidae

 

[whisk]

thanks again Cranberry, youre the best!
I found some info on them:
These worms are virtually harmless. These animals brood their larvae in either the operculum itself, or within the tube until ready to metamorphose, and then release very short-lived planktonic larvae. These larvae often settle within minutes (and almost always less than an hour) of their release, and can therefore spread rapidly within a reef aquarium. This generally happens early in the life of the aquarium, and in a well-maintained, clean aquarium, the initial population explosion of these small worms quickly slows and they are almost never a problem in any aquarium. If the population continues to climb to the point that all surfaces in the tank become encrusted with these worms, it likely indicates a high suspended organic problem, and you should be more concerned with your water quality than the presence of these polychaetes.

 

[Pagan]

Is there anything that eats them....?