Landine
From Tardis Wiki, the free Doctor Who reference
Landines (or Guardforms) are specially modified and trained to be guard animals. They are gentcially modified from wild creatures and are trained to protect their owners at any cost. They are polymorphic, but they are generally in one specific form.
The Landine who was with the Annarenes on Earth took the form of a small black dog with blue eyes. After they were killed, the Landine was passed along to Countess Gallowglass and stayed in the form of a cat. (DW: Relative Dementias)