Marine Worm- Good or Bad?

[lorsinger]

Yesterday I saw a worm in my tank that looked a lot like this: http://etc.usf.edu/clipart/6900/6942/marine-worm_6942.htm
It was fast moving. Does anyone know what this is, and is it good or bad?

 

[olemiss reb]

I'm gonna say bad, check the eunicid section for a match-- http://www.chucksaddiction.com/hitchworms.html