There are at least two schools of thought with the Fireworm vs Bristleworm. That's the problem with common names, there's no concensus.
1 - Fireworms are a specific colorful Specie of Carribean Polychaete named Hermodice carunculata that eats soft corals such as Xenia, Gorgonia, and mushrooms.
2 - Fireworms are the type of Polychaete that have rows of either Calcarious or Silica spines for protection.
I belong to group #2.