Star whale
A Star Whale was a giant space-borne creature.
Biology
The Star Whales were giant alien creatures, resembling Earth's whales in basic structure. They had several flippers and tentacle like protrusions down their stomach, as well as smaller spiked tendrils on their back. Star Whales were capable of travelling through space, at speeds comparable to a spaceship. Though they could communicate in an atmosphere, their sounds were too high pitched for Humans to hear. They were capable of bioluminescence, with glowing patterns around their tendrils. (DW: The Beast Below)
History
An ancient and benevolent species, the Star Whales had, according to legend, guided early space travellers through dangers on their journeys through space. By the time of the 29th century, the species was believed to be all but extinct save for one individual. When Earth was facing destruction because of solar flares, that Star Whale was drawn to Earth. All the peoples of Earth had managed to escape in massive city ships, but the people of the United Kingdom lacked the supplies to create an engine. The Star Whale intended to offer its services to the stranded people.
Unfortunately, the people of the UK misinterpreted this gesture of good-will as a lucky coincidence and captured the whale, building their ship right on its back and carving an opening to its brain to torture it into moving. The city built on its back became known as the Starship UK. While the government realized the moral problem, they believed that if the Whale was freed, the Starship UK would be destroyed, killing the population. To deal with this, every five years, they revealed the truth to citizens one at a time, and allowed them to vote on the matter, either choosing to "Forget" or "Protest"; Forgetting meant their memories would be erased so they didn't have to live with the guilt, but Protesting merely meant that that particular citizen would immediately be fed to the Star Whale. Every year the overwhelming majority of citizens chose to Forget. Similarly, Queen Elizabeth X (Liz Ten for short), whose body clock had been halted and who had ruled the British people for three hundred years, was faced with the choice to Forget or Abdicate every time she found out the truth; Abdication would free the Star Whale, but as previously stated, it was believed that this would destroy the Starship UK. It is unclear exactly how many times she discovered the truth, but every time, she too chose to Forget for the good of her people.
When the Doctor and Amy Pond came to the Starship UK circa the 33rd century, they began to investigate the ship. Along the way, Amy stumbled into a voting booth and learned the truth, only to choose to Forget. Eventually the Doctor discovered the heart of the ship, where Hawthorne and his workers were torturing the Star Whale with electric shocks to keep it moving, and faced the impossible situation. Seeing no other reasonable options, the Doctor was prepared to lobotomize the Space Whale so it would no longer feel pain from the torture. Amy, however, noticed the Whale's neural tendrils affectionately playing with the children. She quickly put the pieces together and ran over to the control system to press the "Abdicate" button (with Liz Ten's hand), freeing the Whale. The ship, however, was not destroyed as was originally feared, but instead started to move faster; as the Star Whale had come willingly and was still willing to help the people of the UK, it was able to move more freely without the torture dulling its senses. (DW: The Beast Below)