What alien species did you want to know more about?

[KingAlanI]

All of them. I'm a sucker for canon details in general. The first particular example that comes to mind is Andalite civilian culture.

Skrit Na seem like a great in character explanation for stereotypical aliens, not sure what else to do with them.

[NothingFromSomething]

Yeah, I would have loved to get a little deeper into the Andalite stuff, it's one of the reasons the Chronicles book is probably my favorite overall Animorphs entry.

[KingAlanI]

Yeah, The Andalite Chronicles is definitely one of my favorites so far in my reread.

[Bootlebat]

What I think is weird about the Skrit Na is how they apparently haven't made any progress/change since the time of The Ellimist Chronicles (at least 65 million years ago)

[NothingFromSomething]

They're just said to develop at different rates, from memory.  Like the Andalites are more advanced than humans, but they progress slower, aren't quite so entrepreneurial and exploratory.  Probably the same with the Na, they just got to a point they didn't need any more stuff for whatever their biology compels them to do, scavenge and steal and screw with, and just kinda plateaued. 

[Azguard]

The Venber and anything about the Anati area

[Tim Bruening]

The Venber and anything about the Anati area

The Crayak and the One!

[Dylan]

The Anati, they are soooooo mysterious and yet the battle at Anati plays a part in starting the final arc!

[TheWolfEmperor]

The Kelbrid were pretty much just an endgame piece of the puzzle, though, we didn't need to know anything about them because their purpose was just to exist, as a one-book plot device, a deterrent.

I have always held to the belief that the Kelbrid was a parting gift from Applegate and Grant to the fans, or more specifically, the fanfiction writers.

Temrash mentioned the conquest of two other alien races, the Makk and the SStram. I would like to have seen that explored more thoroughly. But then KA also refers to Subvissers as Undervissers, so I think it was still in the early stages when she was trying to plan what direction he series would go in.