Bristle worms are good/harmless detritus feeders and although most find them ugly are nice to have. However, if they get larger/more numerous it's a good sign that you may be overfeeding!
Fire worms are more harmful and can actively hunt live prey.
If you see it all the way out during the day it may be a fire worm as they are active during the day sometimes. Bristle worms are almost always only seen at night.
If you want to get rid of them there are several designs for traps floating around these forums if you do a search but ultimately I'd keep it!
Some other notes, don't pull on it, they are segmented so it will just regrow the lost bits. Obviously do not touch with bare skin of any kind, reactions are different for different folks but it's always going to be irritating at the very least (think fiberglass insulation).