Monoid

Monoids were a humanoid species who travelled on the Ark with the last of the humans.

Biology
Physically, Monoids are about the same height as humans, but their skin is dark and scaly. They all have mop-top hair, although some have lighter hair than others. Their feet are like flippers, which probably contributes to their slow movement. They have no visible mouths, relying on sign language for communication, although they apparently eat and drink through a hole in the side of their necks. The most striking feature of the Monoids, though, is the single eye in the center of their heads. Instead of names, the Monoids had numbers based on rank. (DW: The Ark)

History
In the 101st century, one of the shows in New Earth Republic was Confessions of a Monoid. (PDA: Synthespians™)

The Monoids arrived on Earth long before the Ark went into space. Their own planet was dying, and they offered their services in return for a place on the Ark. The humans accepted and welcomed them on the trip. While travelling, the Monoids fulfilled a near-slave role, carrying out menial tasks for the humans.

After several hundred years of travelling, the Ark neared its destination, Refusis II. The Monoids staged a revolution and made the humans their slaves.

They developed a means of communication and created heat prods to keep their captives in order. The Monoids completed the humans' statue by adorning it with a Monoid head instead of the intended human one.

In this they planted a bomb to be detonated when they abandoned the Ark and left the humans behind. After Two did not complete communications from the surface of Refusis II, the Monoids began a full scale landing. However, mutiny resulted in the deaths of several Monoids as fighting ensued. The bomb was ejected into space by the humans, saving the Ark. The surviving Monoids returned aboard. The Refusians welcomed both species to their planet if they were to become friends. Both agreed. (DW: The Ark)

Other References

 * Monoids could be found at the Pridka Dream Centre. (NA: Infinite Requiem)
 * The Tenth Doctor compared the human Badgers and the Ood to the Monoids, all three being slave races. (NSA: The Pirate Loop)