thats a tough one there are a couple different kinds of worms some good, some bad, i will see if my books can come up with any distinguishiing charachteristics, also you might wanna id it before you let it have free reign in your tank, its prolly in the rock, and the best way to get it out is to do a high salinity dip i think the salt level should be like 1.035 but not sure on that, hope this helps,
Brahm