Lore
Note: this is entirely optional and you do not have to adhere to this!
Terratrix are created from the very essence of a location itself. Think about your favorite place, or a place where a memorable event occurred. Terratrix are born from the feelings one holds for that specific location and represent them as well. For example, a terratrixie born from happy emotions tend to have an upbeat and friendly demeanor, while a terratrixie born from a place with sad memories would be more melancholy.
Anatomy
All terratrix have these essential traits: horns, tail(s), markings, a core, and a terrarium. The horns, tails and markings contribute to the terratrixie's resemblance to the location where it was born, while the core and terrarium are a terratrixie's most important organs. The core powers the terratrixie and holds all its emotions and ties to the location, similar to a human heart. On the other hand, the terrarium is a representation of the location the terratrixie is based on; it doesn't have to be entirely accurate but it is important to a terratrixie's daily life. A terrarium can provide comfort, safety (as it is made of a hard, clear substance similar to glass but less fragile) and also directs how the terratrix acts (similar to a human brain).
Additionally, terratrix can have paws or hooves in place of human hands and feet. The same applies to ears; besides round human ears, they can also have animal and pointed ears.
Core
The core of the terratrixie is, as mentioned earlier, similar to a human heart. It is always located somewhere on the terratrix’s torso, whether it is on the back, side or front.
Terrarium
The terrarium of a terratrixie floats around it and is attached by an invisible force. The Terratrix or is able to retreat inside their terrarium and lives inside of it.