Fledershrew

Fledershrews were a species of bat that were near extinction on their home planet. During his seventh and eighth incarnations, the Doctor allowed an entire colony of Fledershrews to live in his TARDIS. (AUDIO: Black and White, Relative Dimensions)

Shortly after the Eighth Doctor's granddaughter Susan Campbell and great-grandson Alex Campbell arrived in the TARDIS to celebrate Christmas with him and Lucie Miller, the Fledershrews were all killed by the Blitzen fish. (AUDIO: Relative Dimensions)