The only two species of bristleworm/fireworm that I know to be dangerous are very recognizable both by appearance and habit.
The caribbean Bearded fireworm is big. Real big. Up to 3 feet long. Bearded because it's bristles form very thick bushy tufts that are long and bright white. Being so large and formidably defended, they have very few natural predators and as such are quite fearless. While most worms are nocturnal, stay mostly hidden, and/or retreat from nearby movement, the Caribbean Bearded worm has a very "I don't give a darn" attitude. Also, other than being very unpleasant to accidentally touch, they are really only dangerous to non-encrusting gorgonians. They will essentially pick a branch of the gorgonian and, pardon the term, deepthroat it, gumming the tissue to death for digestion. As you can imagine, by behavior alone, this worm is very easy to identify.
The other one is the Bobbit Worm. Not kidding, that's the name. It's much stockier in build and has proportionally larger mouthpieces, giving it a terrifying appearance. Like a cross between "Tremors" and "Alien". It stays beneath the sand until an unsuspecting fish moves over it. It then bursts out with incredible speed and bites, hard enough to actually cut smaller fish in two. Again... pretty easy to recognize.
Both of these worms would starve in the average SW tank, with inadequate supply of appropriate food. Frankly, if someone had a half dozen Caribbean Bearded worms, I'd put them in my tank just to prove a point.
The worms are our friends. Unless you are overfeeding the tank to the point of allowing the worms to grow to "maximum adult size" there really is nothing to worry about.
I cannot be 100% sure of the worm in that other thread, but it *could* be a juvenile bearded. In which case... cool!
I'm sure it will be willing to scavenge leftover fish food like any other worm, but it's natural prey are gorgonians, and probably not in that tank. I doubt any other coral or fish has anything to fear from it.
Regarding the hallucinations: Not the worm's fault! LOL Those bristles are actually hollow barbed tubes of calcium carbonate. Hollow is the key word here. If he really was hallucinating, it wasn't the bristle itself, but rather bacteria and other contagions from the tank water itself, which were brought into the wound by the hollow bristle. Appropriate treatment is a vinegar soak, followed by hot water soak, followed by a doctor's visit, mentioning exactly what happened... and antibiotics to treat the inevitable infection. Tetanus booster also recommended.
