The Arkonians were a humanoid species.
Arkonians did not appear to have sweat glands and their bodies' hydration system was not based on water. Instead, they drank a brown liquid that they called "tarrat-aash". Their saliva had healing properties, as it could quickly repair skin abrasions. Arkonians could eject their saliva as a projectile while hissing. Their cellular structure was not capable of handling rapid temperature changes.
In the early 2050s, the Arkonians achieved warp capability and the Vulcans soon made first contact with them. The first contact mission wasn't successful in establishing good relations. The Arkonians proved to be suspicious and deceitful and the Vulcans were soon recalled. For more than a century after that, the Arkonians and Vulcans had rocky relations. Arkonian destroyer captains would be wary of any ship that had even a single Vulcan on it.
In 2152, the Arkonians made first contact with Humanity through Enterprise NX-01. Captain Khata'n Zshaar had been sent to patrol a system the Arkonians had annexed, and sent a shuttle piloted by Zho'Kaan to investigate a shuttlepod that had been sent from Enterprise. When both shuttlecraft disappeared, the Arkonians and Enterprise had to work together to find their lost crewmen. (ENT: "Dawn")