Bristle or Fire or Bobbit Worm?

[Macbalacano]

Hi everyone just saw this tonight from the live rock I bought a couple of days ago. Is this just a harmless bristleworm? Or is it a bobbit worm or fireworm?

 

[Gtinnel]

It looks like it’s probably a bearded fireworm.

 

[Macbalacano]

So I’m just going through pictures and other threads and looks like fireworms have red things on their sides - this one does not appear to have them?

It looks like it’s probably a bearded fireworm.

 

[EeyoreIsMySpiritAnimal]

Hi everyone just saw this tonight from the live rock I bought a couple of days ago. Is this just a harmless bristleworm? Or is it a bobbit worm or fireworm?

Definitely not bobbits.
Possibly fireworms but NOT the bearded fireworms that eat coral. The majority of fireworms are harmless detritivores and just have a stronger sting when we touch them... but you don't really want to touch regular bristleworms either

General rule of thumb - if the bristle/ fire worms only come out at night or right after you feed, they are usually harmless. The harmful ones are much bolder and will be seen crawling on coral, not just poking out from under rocks.

 

[JoJosReef]

Second what @EeyoreIsMySpiritAnimal said. Not a Eunice worm -- they have a whitish band right behind the head, 5 straight outward pointing antennae in a star orientation in the front of the head and rarely come far out of their holes. You can sometimes see their mandibles when they are grabbing something, which is impressive and freaky.

So more the bristly/firey type. If it really bothers you, you can try cutting a piece of cocktail shrimp, letting it sit a bit in water during the day and then put it inside a short bit of women's stockings tied at the ends, drop it in the tank at night and then pull out the stuck bristle/fireworms in the AM (use tongs, please). Their bristles get stuck in the stocking mesh.

 

[Gtinnel]

Maybe Im not correct on what I believe I see in the picture. Where I drew lines is there not little red tufts between the bristles? Also is there a noticeable red frilly thing on the head where I drew the arrow?

The dead giveaway on a bearded fireworm is the red frilly thing (caruncle) on its head. It is such a noticeable trait that it’s even in the bearded fireworms scientific name (Hermodice carunculata)

 

[JoJosReef]

Maybe Im not correct on what I believe I see in the picture. Where I drew lines is there not little red tufts between the bristles? Also is there a noticeable red frilly thing on the head where I drew the arrow?

The dead giveaway on a bearded fireworm is the red frilly thing (caruncle) on its head. It is such a noticeable trait that it’s even in the bearded fireworms scientific name (Hermodice carunculata)

Really hard to tell from the photo. There's some pronounced shadowing, which might be giving off the darker "tufts" between the white bristles.

Overall good photos OP, just maybe at different angle or lighting if you want a positive ID.

Gluck with your rock monster!

 

[Kzang]

fire worm. I had that exactly, and it kept taking chunks out (twice) on an anthia in QT that was hiding in a zoa colony.

 

[Macbalacano]

Thanks very much everyone! This has been super helpful. I'm not going to have inverts or fish in here for another few weeks, just coral. So I'm going to monitor and hopefully see it come out again. If I'm able to take it out, then I will, but it sounds likely that it won't be a troublesome hitchhiker, so I'm not going to stress about it too much. Really appreciate all your help!

 

[WheatToast]

Really hard to tell from the photo. There's some pronounced shadowing, which might be giving off the darker "tufts" between the white bristles.

Though somewhat difficult to see, the gill tufts do overlap with the setae.
The fireworm Pherecardia striata for comparison: