Cant remb is a 6 line will eat them?
If small ok. They just look unattractive. They are super small. Not sure what the growth rate is?
I don't think bristle worm. I have thousands of worms, sand bed, rocks, super thin like thread and white/ clear. They are good, they eat particles.
They don't cut you, the spines come off in your skin. I have been caught out often. No dramas
That was the wrong pic. Sorry. I think they look kinda cool
The original question said the worms are 'on' the rock. I assume attached. I have these worms that have a bit of a 'pipe' that they extend and retract from. They are like mobile hair that reaches to fetch particles to feed on.