we have a 6 incher, scares the wife, she thinks it's a snake, mainly hangs out in the zoa garden, never bothers anything, excellent scavenger, keep it. the zoas where it hangs out are the healthiest zoas in our tank

Well I didnt get a chance last night to pull the worm out of the tank. Which is a shame because I woke up to a blue legged hermit crab torn to little bits.

Is it possible to get a clearer photo? I'm probably wrong, but from the pic you posted it may not be a brislteworm, but a peanut worm. I've seen the odd bristleworm during the day in my system, have also seen my cleaner shrimp yank a small one & eat it. Since you mention you see these primarily at night is why I think it might be peanut worm. I see a number of these extend from their hole at night, more so than bristleworms. It that's what it turns out to be, they are definitely harmless.

You can almost certainly blame another hermit for that one I think.

+1 unless it was just an empty molt shell.....

I just found the same thing, bought an arrow crab. He should hunt down the beast.

While I don't think they're a problem in the tank, I'm also not a fan of getting their fibreglass-like bristles in my hand. I don't have any that I'm aware of in my tank, lots of other critters though.

One big sucker (over 8" long) actually killed one of my seahorses years ago. I was watching the tank & it came out of its hole and bit the seahorse in the chest. The pony thrashed about but the worm didn't let go for over 10 secs. I ended up tearing apart the tank to catch the worm out. The pony died a couple of days later. So I'm in the "not a fan" category.

Small ones I have no problems with. Big ones I catch out and kill. A sign you're overfeeding is when there are lots of bristle worms.

Anthony