[infamous]

I haven't experienced bristleworm myself, but from what I understand, their bristles will start to wear out your rock. Carve it out as it (and it's bristles) moves around for an extended period of time. I think that some people don't mind them and they can live in your sump as well. But, they could end up back in the tank. They definitely aren't a friendly creature and I would suggest removing it from your tank as they will harm your livestock. The Coral Banded Shrimp is also a natural predator of the bristleworm and could be a good aid in it's removal. Good luck with the bristleworm!