Please ID for me

[The Newbie]

Hi Guys
Can anyone tell me what this is-It is a string/thread like creature that comes out my live rock at night when the lights are off,Its pretty long and goes around on the rock and on the substrate.Any ideas?is it good or bad?

Thanks

 

[RiaanP]

its a worm

well, actually I do not know what type of worm. But if it goes down to the substrate and feed there I would reckon its a detritus feeder. And then its OK to have.

 

[The Newbie]

Thanks,
it stays in the live rock and the body extends to where it goes