Eknodine

The Ecnodeen are a species of aliens that took over the bodies of old people in a dream created by the Dream Lord. The Doctor talks to them as if he knows of them, indicating that they do exist.

Physiology
The Ecnodeen are aliens inside of human hosts. Only the eyestalk is seen. They arrived on Earth because their other planet was taken from them, and they want to do the same to Earth.

Abilities
They could turn people into dust by spraying a green cloud over them. They could also use humans as hosts and allow them to live longer.

History
The Ecnodeen that the Doctor, Amy Pond and Rory Williams encounter said that they were driven away from their home planet and came to Earth where they took hosts to stay inconspicuous.

They chased and attacked The Doctor, Amy and Rory after they found out what they were and cornered them in Amy and Rory's house and attempted to gain entry. One under the guise of Mrs Poggit killed Rory after climbing up to the top floor window and turned him into dust. Amy and The Doctor decided to kill themselves hoping that that was the dream and ran a couple over before crashing into the house and dying.

Behind the Scenes

 * It is possible that the thing that has driven them away from their planet is the Silent Menace as this has also driven the Saturnynians from their home planet to Earth.