Long brown floating "string" in 2 mo. old reef tank

I've seen two of these "worms" now. When I've gone into the tank to get them, they break into several pieces as soon as I touch them. They aren't yellow-ish, and there are no legs (I've looked with a magnifier as best I could) and they seem to be about 5 inches long. Any idea what they are?

The color on this photo is bad, but it's just a plain light brown.

Thanks
Leigh