Fridge Logic: Some of the evolutionary roads are a bit strange. The Ocean Phantom is a descendant of the Portuguese Man-O-War, which itself is a composite creature, meaning each creature making up the Man-O-War evolved together into the Phantom. And some species and even entire families that are well-known for their ability to adapt, like bats and rodents, just up and die out completely for no rational reason.
They explain why mammals die out. The world grows more and more warm and humid, conditions where mammals are at a disadvantage against birds and reptiles. Yes, we are in the Age of Mammals, but Earth also went through an Age of Trilobites once, so…
Though an existing phylum taking over the old dominant phylum when the previous one still exists (as cephalopods do here) hasn't happened since animals first evolved. And was there actually an age where trilobites were dominant or just where they were very common?
But the world was warm and humid like that. It's called "Eocene period". Guess which group of animals came to the top (hint: not insects).
Also: how do the bumblebeetles mate? They only live for a day, and as far as can be told they do not have some special mating ceremony like, say, california squid.
According to the book, they're sexually mature and mate as larvae ("grimworms").
The Deathbottle spreads its seeds by luring Bumblebeetles into its inner cavity, where the seeds stick onto the insect. It does so by imitating a dead Flish. But earlier on, the program made it clear that Bumblebeetles don't even crawl into real Flish carcasses either; they just land on them, and it's the larvae that dig themselves into the meat.