Fledershrew
From Tardis Wiki, the free Doctor Who reference
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. (BFA: Black and White, BFA: Relative Dimensions)
They were all killed by the Blitzen fish. (BFA: Relative Dimensions)