Woprats were a long-extinct species from Gallifrey. The Second Doctor was surprised to find one in a Type-one TARDIS and wished to investigate. Before he could, Victoria screamed and scared it off.
Woprats were built like small dogs and appeared like rats, except they had fifteen long, multi-jointed limbs arranged like a spider. Older ones had thin, grey hair. (PROSE: Heart of TARDIS)