Pig-rat

A  was a kind of non-sentient rat which lived on Gallifrey. They could eat through Time Lord flesh, at least according to a threat Janartis once levelled against Romana II. Indeed, Romana's home of Heartshaven was once overrun by them. (BFG: Panacea.

They once overran a medical station in the Outlands to which Leela once had to go during the civil war between Romana II and Pandora. (BFG: Fractures)