Arcateenian

The Arcateenians are a race of humanoids from the Arcan system.

Biology
Arcateenians are made mostly of liquid, yet adopt a humanoid form. (TW: Cyberwoman) Their internal structure can be seen faintly through their skin. They have tendril "hair" on the top of their head and on their backs. They have five long, slender fingers and have a blue tint to their skin, although their aura gives off colours that are invisible to the human eye. 

To maintain their shape on any planet with a stronger gravitational field than their own, they require large amounts of energy. (TW: Greeks Bearing Gifts)

They share many aesthetic qualities with Oblivioners who hail from the same galaxy. (The Torchwood Archives) Similar to the Oblivioners, Arcateenians are able to inhabit the body of a Human.

An Arcateenian's skill-set varies depending on which planet it hails from. Arcateen IV is the main seat of government in the system. Arcateenians from this planet have developed a way with words, although this often works against them as they can occasionally take up to eight hours to complete a conversation. At the other end of the scale, Arcateenians from Arcateen V have developed a concise and poetic way with words meaning they are often very creative. (The Torchwood Archives)

Technology
The Butterfly People have faster-than-light travel capabilities, including transporter systems and superluminal communications technology. (TW: Greeks Bearing Gifts, SJA: Invasion of the Bane). They had developed this by at the latest the early 1800s. (TW: Greeks Bearing Gifts)

The Arcateenian in SJA: Invasion of the Bane appeared to have wings allowing it to fly without the use of a transporter system. It is possible


 * Sarah Jane Smith's friend, the star poet, however did not seem to use a transporter, but when leaving simply flew away into the night sky.

Mary, a Butterfly Person, was shown to have super-speed and strength, telepathy and the ability to inhabit the body of a Human. (TW: Greeks Bearing Gifts)


 * Whether all Butterfly People have these abilities or whether these abilities were technology based is unknown.

History
In the early 1800s, a criminal Butterfly Person was sent to Earth from Arcateen 5 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 Arcateen 5 was run by an oppressive government which forced worship and exiled prisoners like herself. (TW: Greeks Bearing Gifts)


 * Mary may have been lying about Arcateen 5's history.

By the 21st century, there appeared to be a more benevolent government on Arcateen 5, and peaceful star poets from the planet would travel to other star systems with their poetry. One such traveler met Sarah Jane Smith and gave her a superluminal communications device. (SJA: Invasion of the Bane)