I have at least two large 1-2 ft worms just like that in my tank and just assumed they were large bristleworms. I have had snail deaths (some turbos), but just assumed that they were from not having enough algae for them to eat, and the said detrivores were just cleaning up I believe. I managed to get one with some surgical forceps when I was feeding mysis, but he was STRONG and pulled away into the rock. I was shocked at how strong he was.

I have been toying with the idea of a hypersalinity dip for the rock to get them out ...