Plasus, a male City dwelling Ardanan
The Ardanans are humanoid natives of the planet Ardana. They were members of the Federation. Ardanans were very famous for their anti-gravitational city, named Stratos, which floated in the sky. They are also known for their export of zenite.
As of 2269, their society had evolved two castes, the Stratos city-dwellers who devoted themselves purely to art and culture, and the surface-based Troglytes
City dwellers ruled the planet from Stratos trough a council existing solely of their class, justyfing the total suppression of the Troglytes based on the wideheld belief that as an inferiour species the Troglytes were incapable of anvanced culture like there existed on Stratos. As of 2269, Plasus held the position of high adviser of the council
Troglytes on the other hand were considered to be mentally inferior, and therefore performed all the physical toil necessary to maintain Stratos, most notably mining Zenite. Unknown to both city-dwellers and Troglytes however, this mental disadvantage, while real, was only the result of exposure to a gas emanating from unrefined zenite, and furthermore, fully reversible.
Troglytes felt suppressed and wanted acces to Stratos, and at some point a resistance group known as the disrupters was formed, mainly under the impulse of Troglytes that had been away from exposure to the gas due to duties in Stratos. They tried to put pressure on the city-dwellers by witholding zenite and capturing hostages. When the Enterprise visited Ardana in 2269, they've been active for several months. Due to intervening by the crew of the Enterprise, this situation was exposed to starfleet, and apart from a direct suggestion to start using breathing masks in mining so that the troglytes could recover their full mental capacities, the people of Ardana were referred to the Federation Bureau of Industrialization to resolve their differences. (TOS: "The Cloud Minders")
Several power relays in use aboard a Retellian freighter were acquired from an old Ardanan shuttle. They weren't designed to carry more than an average current. (ENT: "Precious Cargo")
It is unknown how the conflict between Troglytes and City Dwellers evolved after the intervening of the Enterprise. Also, it seems strange that such a system could have existed on a federation world in the first place, as it seems from the federation position on the Bajoran D'jarra that caste systems were condemned by the Federation at least in the 24th century. However from the surprise and dismay when Kirk found out some of the specifics of Ardanan society it might be speculated that the Federation was not fully aware of the situation at the time.
Although Plasus calls the troglytes "a conglomerate of inferior species" at one point, it still seems both city-dwellers and troglytes form one and the same species, as this was an essential plot-point. His quote might perhaps be atributed to the wideheld belief of superiority on Stratos