Eunicid - harmless or harmful?

[Reefer Dan]

I found this worm in my tank tonight. Every time I went to grab it, it would retract pretty quickly (Seemed like it had good eyesight) .

I plan to try to catch it, but I wanted to get thoughts on it first.

thanks!

 

[((FORDTECH))]

Looks like 2 antenna on its head yes I would say Eunice worm