Magnedon

Magnedons were metallic, lizard-like creatures native to Skaro. They were similar in shape to a crocodile, but with eyes on stalks and spines along their back. Their bodies were held together by an internal magnetic field and the First Doctor believed that they could attract other metallic creatures to prey on them.

Many magnedons were killed during the Thousand Year War, though their bodies were kept in relatively the same conditions. Their metallic physiology prevented them from decaying, thus leaving them intact. The Thals used their bodies to recharge their hand lights. (TV: The Daleks)

A magnedon was kept on Station 7 by the Space Security Service. (COMIC: The Only Good Dalek)