I only have two comments: 1) referring to fireworms as "pretty or ugly"
is in the eye of the beholder. Perhaps one of the dangers of Hermodice
from the Caribbean is precisely the fact that they are quite brilliant in
color, and unexperienced persons try to place them on their hands for
closer examination. A bright red, or bright green worm with showy whyte
tufts of bristles along it's sides can be quite "showy", and I have seen
quite a few people get stung because they want to take the worm by hand
so they can place it in a jar.
2) Some fireworms have the capacity for consuming corals, but I
don't know of any studies showing this is their only, or preferred food.
As far as I know they are all omnivorous.
Edwin