I recently read old MK's quotes as well as descriptions of Guars on the old Morrowind website. I made a quick search here but I founded no mention of them.
Guar (g'war): The domesticated guar represents milk, meat, leather, and transport for Vvardenfell's settled Velothi ranchers and Ashland nomads. In its natural state, the aggressive and territorial wild guar is hunted for meat and hides, and the larger feral tiger guar is a highly prized game animal for noble huntsmen.
Another little known fact is that the Imperials often refer to Guars as 'Tigers'. Here's why: during a tour of Morrowind in the earliest days of the Armistace, Tiber Septim became enamored of the beasts. On the mainland, and specifically the Deshaan Plains, Guars are striped. This, coupled with the fact that His Holiness was never able to pronounce 'Guar' correctly (his troubles with the provincial Chimeric tongue is legendary), led to Septim finally callings them 'Tigers', from a fabled recollection of a storybook beast he loved as a youth. The new name stuck. Even now, Dres slavers often refer to their cattle-Guar as Tigers.
They are arthropods. In fact, they were created by Vivec to hunt Dreughs during a time-lost campaign against the Altmer of the sea.
I just want to know if we are taking these informations into account in TR and how. I have not seen striped guar leather in TR_Data textures but it is doable, and we can easily emulate the arthopodic aspect of Nix-hound, allowing him to "swim" (walk underwater) and giving him a water breathing skill/power.
Moreover, I think these pieces of lore are a good base to elaborate more contents: Books, new monsters (like a "true" aquatic version of Nix-hound), new misc items...