Worm ID

[Drock169]

Any one able to ID this. Its some sort of nocturnal worm with swims with an undulating motion ( i think thats the word i'm looking for). they range for a cm to this one being the largest at about an inch.

I'm trying to figure out what is eating my soft corals. I was thinking maybe it was a nudi (because of the white marks that are left when the coral was eaten) but I have no idea. I'm almost tempted to give all of my LR a dip in Lugol's.

Any help is appreciated