The Arkonians were a humanoid species.
Arkonians did not appear to have sweat glands. Their bodies hydration system was not based on water. Instead they drank a brown liquid that they call "tarratt-aash". Their saliva had healing properties, as it could quickly repair skin abrasions. Their cellular structure was not capable of handling rapid temperature changes.
In the early-2050s, the Arkonians achieved warp-capability. 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 human shuttle that had been sent. When both disappeared, the Arkonians and Enterprise had to work together to find their lost crewmen. (ENT: "Dawn")