JynxGirl, have you read ReefInvertebrates by Calfo? it goes into a lot of detail on both good and bad worms.

the uckiest worm I think would be the dream weavers... they slime your snails w/ narcotic gell then munchem, leaving you nothing but a shell and slime in the AM.

I think SamIAm had one at one point.

Anyhow, coralvores have distinctive mouth parts that can be identified if i remember correctly, and other than that, bearded fireworms are the only real concern, so I would just start comparing pictures on the internet, or with that book if you can get it, and be at peace.