Looks like a detritus worm. Nothing to worry about, it’s a sign you have a healthy ecosystem in your aquarium. If there’s a LOT of them (which from what I can see, there’s not) it’s because there’s excess waste/food they’re feeding and thriving off of. Water changes will decrease the numbers, but you’ll honestly never be rid of them. I barely notice them in my tank any longer but I know they’re there.