Different Heights

They're either short medium or tall

ZoParvus is the class for small Pokimon.

ZoMedius is the class for medium Pokimon.

ZoMagnus is the class for large Pokimon.

What makes the three classes so different from each other? That has yet to be researched.

ZoRegnum is the class for Pokimon with much power or authority, regardless of size. Hard to catch. I suggest not doing it.