Their government was known as the Tholian Assembly; in the Alpha Quadrant, this political entity was neighbor to both the United Federation of Planets and the Klingon Empire. (TNG: "Conspiracy", "Reunion")
While encounters with individuals of the species were rare (in at least the 22nd and 23rd centuries), some aspects that were common to the species as a whole were crystalline external structure, and high body temperature (257 degrees Celsius). ("The Tholian Web"; ENT: "In a Mirror, Darkly")
An early encounter with members of the species ("In a Mirror, Darkly") showed some members to be quadrupedal with two arms, while others had eight limbs. (Decipher RPG: Aliens) Still other members of the Tholian species were crystalline bipedal humanoids. (TNG comic: "War and Madness")
- These may be due to caste or gender dimorphism. Some may be the anatomy of Tholians from different continuities.
At least some Tholians were long-lived. One, Loskene, was a military commander who had encountered both the Constitution-class USS Enterprise in 2268 ("The Tholian Web") and the Galaxy-class Enterprise-D a century later. (TNG novel: Vendetta)
Individual Tholian cells were regular polyhedrons that had an electrical charge. (Star Fleet Medical Reference Manual)
In this continuity, caste dimorphism was indicated by an individual Tholian's crystal form. For example, officers were sessile tetrahedrons; those tasked with moving officers were hexahedrons; and commanders were dodecahedrons.
Tholians were grown from eggs that may drift through interstellar space, and hatch when exposed to Pertack's radiation. This radiation was also their food source; without a steady diet of it, Tholians will collapse back into the egg from which they hatched. (Orion Press: "Ad Astra Per Aspera", "Return to Xantharus", Old Feuds, Chekov's Enterprise)
About 17 years after Enterprise's contact with Loskene's squadron, there was an engagement between Federation and Tholian forces in the Cobol Epsilon Tau system, USS Kongo immobilized a Tholian destroyer but was destroyed by a Tholian battleship. There were no survivors. (Research Anthology: "Cross Fire: The Tholian Slaughter")
- In the Orion Press continuity, there had been no contacts between the Tholians and the Federation between 2268 and late 2294. There were no Tholian embassies nor consulates, though there had been diplomatic relations between the Tholians and Vulcan for 300 years. (Orion Press: Chekov's Enterprise)
During the 2340s and 2350s, there were many border skirmishes between the Federation and the Tholian Assembly, including an attack on Shadowstar Station in 2354. (Star Trek: Shadowstar Station: "Blindspot") These low-intensity conflicts were collectively known as the Federation-Tholian War, and eventually gave way to greater contact and trade between the two powers. (The Dominion War Sourcebook: The Fires of Armageddon)
In 2381, after the Borg invasion of the Alpha Quadrant, and the destruction of many worlds and populations, the Tholians joined with other interstellar governments to form the Typhon Pact. (TNG novel: A Singular Destiny)