Star Trek: Phoenix
The Tholian Assembly, controlled by the mysterious Tholian species from its capital planet Tholia, is an extremely xenophobic civilization neighbouring both the Federation and the Klingon Empire.
Tholians are mostly made of a crystalline material. Their biology requires high temperatures around 480 Kelvin (207 °C, 404 °F) in order to keep their hard mineral carapaces sufficiently soft. Although they could tolerate lower temperatures for a brief period of time, Tholians are killed by sustained insufficient heat as their carapace would begin to freeze and crack below ca. 380 Kelvin.
Tholians are hermaphroditic, meaning they possess both male and female characteristics.
Because of their crystalline structure, Tholians are also naturally able to emit various forms of radiation, which – in addition to using it as a weapon – they could modulate in order to communicate over short distances.
There are also a number of biological features shared by the Tholians and the Crystalline Entity.
Tholians employ vessels of a characteristic conical shape able to “spin” energy webs around immobilized enemy vessels. Such Tholian Webs cause damage on contact and eventually contract, destroying any starships within.
Tholians predominantly use tetryon weaponry and are also known to create gateways to the Mirror Universe in order to receive assistance from their counterparts of that reality.
Their shields have a distinctive red hue.
Limited first contact with Humans took place in 2152 due to the Tholian’s involvement in the Temporal Cold War. Over the 23rd and 24th centuries, the Tholian Assembly was embroiled in several small skirmishes with both Starfleet and the Klingon Empire. In 2373, the Assembly signed a non-aggression pact with the Dominion, but continued to have ambassadors on Earth, Romulus and Deep Space 9 at least during the 2370s and 2380s.
It has been theorized that the Assembly actually spans multiple dimensions in spacetime. These claims are supported by their frequent involvement with the mirror universe, as well as their apparent interest in the Temporal Cold War, and time displaced artifacts. It is said that Tholia inhabits a region of space where the borders between dimensions are unnaturally thin, and that the Tholians have developed technology that allows them to cross those borders at will. In 2409, observation of the Assembly’s activities on Nukara Prime and in the Azure Nebula lends strong credence to the theory.