You really need to give more information that what you did. We need pics or a much much better description... It may be some sand on your rock that got blow from a pump, or can be something that needs to be dealt with.
So just a simple question that you asked really will not work.
i think they are probably small hard tube worms like already said.
Many years ago i asked someone the same question and theyre response was "youre tank is maturing, youre doing something right"
but they can get kinda crazy so i would clean it off
just my two cents