It is thin looks like hair almost but it moves. I have not been able to make out any kind of structure or body that it comes out of. It moves from the rocks to the sand and I have seen it on the glass. Doesn't seem to bother anything. I have seen it retract a little when amphipods crawl on it. The area where it is thicker leaves a white residue (water movement washes it away fairly quickly).
Anyone know what it is?