The zombie villager lost its flesh, turning into a skeletal villager.
It's probably significantly more difficult to cure, though at least it won't eat your brains (hopefully).

(You're right, there's no nose! Now, if we look at a real skeleton, I think we can figure out why).

I have made a full texture pack with these, that also remodels them to look more like skeletons (skinnier limbs) and renames them. Go check it out!