As has been stated, the creature you've seen in the ACN Guild is a mamool'ja - like a lot of monsters and races in the game they actually originated in FFXI (in this case, the FFXI expansion pack Treasures of Aht Urhgan) - they've been newly added to FFXIV, hence why the FF Wiki page on them hasn't been updated to reflect this yet and only shows the FFXI version.

FFXIV lore wise they're not native to Eorzea but originated on the newly discovered 'far western' continent and were attracted east to Eorzea to help cover labour shortages following the Calamity. Because of this they're considered to be in direct competition for jobs with locals and are thus poorly treated, forcing a lot into banditry and crime to survive (the FATE '9 to 5' in Eastern La Noscea directly states this).