are bristleworms DEFINITELY detrivores????

There are tons of varieties of polychaete worms, most are harmless detritivores but there are some harmful ones. I would suggest checking out some of the links in this thread. It might help you determine which type you have. Maybe try and snap a picture of it as well if you can.
http://www.3reef.com/forums/id/worm-pictures-49005.html

There definitely is a type of worm that feeds on live snails, there's more info about this type of worm in the links in the thread above.

 

Fire worms are bristle worms. Just two different species. The link only gives a few examples. There are about 130 different species of bristle worm that can occur in the hobby, about half of which will gladly munch on healthy livestock.

Yes, I have. In a week period, I had a few bristles kill digitata, poci, pulsating xenia, ricordea, and a maxima clam, all of which where perfectly healthy and not "already dead".
AND ;D I even have pics of it happening







Personally, I rid them from my systems or at least segregate them to the sump.

 

i have a large bristleworm... have had him since i started...
about 16" or so last I saw him

 

There's a guy at my LFS that swears on his life he saw a bristle worm take a sailfin tang down.

 

Maybe they were already on their way for some unknown reason when the bristleworm came into play...it is really hard to say....I have so many its impossible to count and have never saw any bad actions from them....
Danny

 

tagging along

 

Nope, and you can even see the other stalks are perfectly healthy where the worm has not been munching. Even those two stalks went on to make a recovery after eliminating the worms. Like I said, some species eat stuff, some don't. With many of the species being nearly impossible to tell the difference, I just eliminate all bristle worms at first sight from now on. Lose a couple hundred bucks worth of livestock to them, and you'll be in the same boat

 

better save then sorry
if there is any left in my tank they will be gone

 

more then likely the snail was already dead

This thread could go on for ever, they often do, but i personally am a firm believer of bristleworms being harmless. I have some pretty big ones in my tank that have never harmed anything and done nothing more then help clean up....