Found this from reefs.org (don't think this is a competitor to this site--seems like info only):
On the glass of my tank, I can see small, white coils that are about 2mm across and have tiny hairs sticking out. What are these guys?
This is probably yet another tube-dwelling polychaete from the Family Spirorbidae. It is yet another harmless filter-feeder that is common in reef aquaria. It is common for these worms to inhabit areas of high water flow, including your tank's plumbing. They readily reproduce via sexual means and often spread throughout the tank, and can generally be considered a sign of a healthy maturing tank.