You are describing a spaghetti worm to my knowledge. You probably don't have too many. Are they out all the time or mainly when you stir up the tank or feed?

Butterfly fishes will eat them and any fan worms you have too. If you like your worm life don't get a butterfly fish they clean out all the worms quickly!

The first time I saw spaghetti worms my first thought was eeeeyyywwww! They are harmless no matter what number you have.