I had one of those in my tank 15 years ago. I could never catch it but when I tore down the tank after it crashed and everything died it was still in there alive and well and over 6 ft. long!
Definately not a bobbit/eunice worm. Just a big bristle. I have them in my tank that size. They are good detritus eaters. Your zoa's are likely dying/melting on their own or something else eating them. Anything more than $15/pp in my tank seems to melt.
Its a bristle worm and ya they can get quite large. Flush it if you can catch it or get something that can eat it, but really shouldnt be to much trouble as they are great scavengers
i have a bunch of 12"+ bristle worms I do net them up when i can i figure there is nothing else in the tank to control them when they get that size so i may as well be the apex predator
My opinion is the same but yes bristle worms are a good cleaner. I personally get rid of them though due to the slim chance of accidentally touching one.