Actually the frogspawn head IS still alive! How, I'm not so sure. It doesn't look too happy though.
Have you examined the skeleton closely? When I was managing a LFS I noticed that a lot of times, when we got bubbles/pearls, those annoying little snails would get in them and cause havoc. This happened all the time on the green bubbles for some reason.
Maybe try doing an iodine dip to weed out the possibility of some sort of parasite? When in doubt, do a water change!
Have there been any changes to the tank recently? This time of year (I remember from working at the store) would get busy with questions because as the weather warmed up, customer's tanks would change, even if only a degree or two, and start a chain reaction. Just some more thoughts.