Did I see a bristle worm? or a potential serpent of death?

[saltwater]

I have had my 150g (no sump) running for almost 2 years. I just swapped everything over to a smaller 75g with sump.

About a 1/2 hour after transferring my rock I look back at the tank and saw a worm that was at least 10-12 inches long inching down the rock with the light off. When I turned on the light it took about 20 seconds to hide. Couldn't see if there was a head. It has a pinkish beige color and had what looked like a thousand feet down the sides. I knew I've had bristle worms for a while... I would even see some come out to feed occasionally if a peice of food falls near one of their holes. BUT THIS THING WAS MASSIVE! Had never seen him before. As far as I know it had never killed anything... should I try to get rid of it?

Any ideas, please?I know It isn't much info to go on...