Yellow thready worm?

[Abiodork]

I have the Aquamaxx HOB refugium. I’ve had this same macroalgae in there for over three months. This little dude, which looks like it might be becoming “these little dudes” is starting to appear. If it was red I’d say my healthy spaghetti worm population in the DT has expanded to the refugium, but they’re yellow. Somewhere around 0.5-1” long. I don’t mind a dirty fuge, but good to know if friends or foe.

 

[ISpeakForTheSeas]

Lots of different species and colors:

Looks like either a hair worm (Cirratulidae) or a spaghetti worm (Terebellide) to me - if the tentacles all come out from a single point, it’s a spaghetti worm; if they come out from basically all over the body it’s a hair worm.