Oroborus

The Oroborus was a snake-like creature able to traverse dimensions and feed on time itself. It could take away chunks of the timeline; the more it took, the more it grew. It could shed its skin just like other snakes. Once it was fully grown it could consume an Earth-sized planet in hours.

The Oroborus made its way to Earth through Alistair Gryffen's Space-Time Manipulator and hid itself in Gryffen Manor's basement. It consumed time until Starkey discovered what was going on and lured it into the Manipulator's path, sending it away. (K9TV: Oroborus)
 * It was unclear whether there was any relationship between this species and the Oroborous Worm.

The signature emblem of the Time Lord, Corsair was a classical depiction of the mythological Oroborus: a snake devouring its tail. Due to this Oroborus' time-sensitivity, it is possible he chose it with this version of the Oroborus in mind. (DW: The Doctor's Wife)

Behind the Scenes

 * Its name comes from ouroboros, the symbol of the circle of life depicted as a snake eating its own tail.