fuzzy worm things

[Whitegurl84]

I have found four of these fuzzy worm things in my 29g bio cube. I'm not sure what they are or were they came from because I have not added anything new to it for about a 6months and these things are just showing up now. Could someone please identifie them?

 

[Crystal A]

Bristol worms a beneficial part of your cleanup crew and free to boot!

 

[Whitegurl84]

Oops I flushed them because I didn't know what they were. Will they attack other things in the tank?

 

[MickeyA]

agree beneficial bristle worm only the bad ones attack and eats stuff but if you have found one theres more in the sand bed and live rock