Mole

A mole was a small Earth mammal.

They were famous for their ability to burrow holes. On one occasion, a mole near Kent quickly dug a number of holes underneath some liquid metal that Daleks had laid down. This destabilised the structure and caused the liquid metal sprayer to entrap most of the Daleks in the metal. As a result, the Dalek invasion was thwarted. (PROSE: The Small Defender)

In the mid-20th century, the First Doctor and Dodo Chaplet encountered a European mole which had been hyper-evolved by an early Gallifreyan time capsule to protect itself. (AUDIO: The Horror at Bletchington Station)

The natives of Tivoli resembled humanoid moles. Indeed, the humans on the Drum used moles in reference to the ghost of Albar Prentis being unfamiliar with his species. (TV: Under the Lake/Before the Flood)