Fossilization isn't just about having or not having bones; it has more to do with the terrain in which they are most likely to die in. If bats don't live in and around areas that are conducive to fossilization, you aren't going to find very many bat fossils.
NOTE: I don't know for sure, this is just my best guess.
Good guess. Bats live usually in forested or bushland areas, or mountainous terrain. Not good for fossilisation.
Jellyfish live in marine environments, get washed onto the shore. Very good depositional environment.
no change over 500 million years. cmon know
No change in those parts preserved - and even there are tiny changes. Exactly what the ToE predicts for highly stable environments. I guess you know little about how evolution works?