The labouring underclass of Ardana, confined to the zenite mines on the surface while the privileged citizens of the cloud city Stratos enjoy the wealth they produce.
The Troglytes are the mine workers of Ardana, a Federation member world seen in the original series episode The Cloud Minders. They are the same people as the city dwellers of Stratos, but generations of separation have left them a despised caste who dig zenite on the surface and are barred from the art and learning of the floating city.
In 2269 the Enterprise comes for zenite needed to stop a botanical plague, only to find the shipment withheld by the Disrupters, a Troglyte resistance group led by Vanna.
McCoy finds that raw zenite gives off an invisible gas that dulls the mind and inflames the temper, which explains the supposed inferiority of the miners. Kirk proves the point by trapping himself, Vanna and the Stratos ruler Plasus in a mine, and then supplies filter masks to the Troglytes.