- You may be looking for their language.
Arcateenians were made mostly of liquid, (TV: Cyberwoman) yet adopted a humanoid form. To maintain their shape on any planet with a stronger gravitational field than their own, they required large amounts of energy. Their internal structure could be seen faintly through their skin. They had tendril "hair" on the top of their head and on their backs. They had five long, slender fingers and a blue tint to their skin. Some Arcateenians had wings and could fly. (TV: Greeks Bearing Gifts, Invasion of the Bane)
The Arcateenians had several methods of faster-than-light travel. They had several varieties of spacecrafts. A first-generation Arcan leisure crawler was described by Jack Harkness as a collector's item. (TV: Cyberwoman) They had large white "hearses", which carried a suspended animation chamber and two battery packs. (TV: Before the Flood) In the 1800s, they also had smaller transporters which could be held in the hand, used dark matter and could teleport the user. (TV: Greeks Bearing Gifts) Sarah Jane Smith's friend, the Star Poet, appeared to use none of these methods, but when leaving simply flew away into the night sky. (TV: Invasion of the Bane)
Jack Harkness described the Arcans as "so boring", claiming that interrogating one could take up to a month for just one question. (TV: Cyberwoman) Mary, an Arcateenian criminal, found her people "savage"; they forced people to worship in huge temples "the size of cities", had execution squads roaming the streets everywhere, and enforced death penalties for almost every crime. As Jack later implied, though, she may have invented these details to create the impression that she had been oppressed. (TV: Greeks Bearing Gifts) Arcateenians had a tradition of burying defeated enemies on a "barren, savage outpost." (TV: Before the Flood)
In the early 1800s, a criminal Arcateenian was sent to Earth with her jailer. She killed the jailer and took over the body of a passing human. She continued to live on Earth for 200 years by feeding on the hearts of other humans. According to her, at that point in time her planet was run by an oppressive government which forced worship and exiled prisoners like herself. (TV: Greeks Bearing Gifts)
In the 20th century, the Arcateenians liberated the planet Tivoli from the forces of the Fisher King, much to the dismay of the native Tivolians, who proceeded to irritate the Arcateenians so much they chose to enslave the Tivolians themselves by the year 1980. The Arcateenians lent a spaceship to the Tivolian funeral director Albar Prentis, who was sent to bury the Fisher King on the backwater planet of Earth. (TV: Before the Flood)
By the 21st century, there appeared to be a benevolent government on Arcateen V, and peaceful poets from the planet would travel to other star systems with their poetry. One such traveller met Sarah Jane Smith and gave her a superluminal communications device. (TV: Invasion of the Bane)
In 2007, an Arcan leisure crawler was spotted flying above Cardiff, and was filmed by some people on their mobile phones, allowing Torchwood Three to identify it. The Arcans were politely persuaded to leave by the institute. (TV: Cyberwoman)
Later that year, Torchwood dug up an Arcateenian prison transport. The criminal previously incarcerated inside tried to infiltrate the Torchwood base to get it back, using Toshiko Sato to do so. She was able to do so, but Jack Harkness had reprogrammed it, causing it to teleport into the sun. (TV: Greeks Bearing Gifts)
Behind the scenes
- Arcateenians are one of the few aliens to have appeared in both spin-offs Torchwood and The Sarah Jane Adventures, but never physically on their parent show Doctor Who.
The Torchwood Archives
According to the non-narrative source The Torchwood Archives, an Arcateenian's skill-set varied depending on which planet it hailed from. Arcateen IV was the main seat of government in the system. Arcateenians from this planet developed a way with words, although this often worked against them as they could occasionally take up to eight hours to complete a conversation. At the other end of the scale, Arcateenians from Arcateen V developed a concise and poetic way with words, meaning they were often very creative.
The Sarah Jane Adventures website
The website for The Sarah Jane Adventures described the star poet of Arcateen V as coming from "a truly benevolent race of beings" and that "her psychedelic aura gives of [sic] colours that go far beyond the spectrum humans can see.