Tiny Black Worms

I found some tiny black worms in my nano when i came home from work today. REALLY tiny, like half an inch long and the width of a thread. I thought they were just detritus or algae at first but when I really looked i could see them moving. They seemed to like the the skeleton of the frogspawn quit a bit, prompting me to freak out. Are these ribbon worms? Anyone had anything like this?