I just want to know.
Okay fine, i'll name them.
1.Cities
2.Vertebrates
3.Invertebrates
4.Unknown Species
I have also come out with more ideas that i'll reveal more of them soon.
Categories need to cover a much wider range of things and be much less specific than the things you've listed.
1. Cities is already covered by Locations and does not need any subcategories. In addition there are only 2 known cities at this point anyway, not enough for a category.
2. Vertabrates and invertebrates are unnecessarily specific and are both covered by Species .
3. There are barely any unknown species worth mentioning and thus no need for a category.
The Brain Slurgs are, for now anyway, known as 'Brain Slurgs' and as such they are not unknown. Even if they would be, its not worth dedicating a category to.