Help? ID, good? bad?

[Mark_C]

Thought it was subsand bryopsis, fished it out and almost ditched it till I realized it was moving.

Polychaete? Terebellid or Cirratulid?

See those as both beneficial worms.

Just want to be sure before I throw it back into tank.

Cheers,
M

 

[saltkreep88]

Common name is a Spaghetti worm. Don't know the exact species but they are beneficial.

 

[Mark_C]

Guess it matches my avatar (and horror) preferences.
It is henceforth named 'Lord Cthulhu'