When I read your post, the first thing that came to mind was Spaghetti worms, which are beneficial. they can be pink, red, or white (at least the ones I have are these colors).
The Vermetid worms I've had put out long, clear "fishing lines" of a mucusy substance to catch food and then reel them in. They are not harmful, but ugly in large quantities. I have taken a screw driver and mallet to knock them off at their base to get rid of them. However, I do find them a fascinating worm with a really neat adaptation for catching their food.