They are spaghetti worms, they come in several different colors, just part of the clean-up crew. They are more noticeable when you feed a lot (same thing as with bristle worms). Sometimes they might irritates a zoa but they are only after leftover food, I feed very heavy and I have hundreds in my tanks.

Holley
I have at least 50 fish, none have been harmed by them![/QUOTE
I must have messed up on the id. Thank you for the correction Holley!