Cryon

The Cryons were a crystaline humanoid race who were the native inhabitants of Telos.

Biology
Cryons were pale and lean, with long fingers and fingernails, enlarged craniums and whitish skin. They also had slow movements and echoing voices. Due to their unusual composition, they could not survive temperatures above freezing and would steam and boil when subjected to heat. (DW: Attack of the Cybermen)

Technology
The Cryons had reasonably advanced technology, but they especially excelled in refrigeration technology. This advanced refrigeration technology is what brought the Cybermen to Telos. They were also able to contact Earth from Telos and had knowledge of the Time Lords. (DW: Attack of the Cybermen)

History
The Cryons built and lived in huge refrigerated cities and lived in peace until they came to the attention of the Cybermen. The Cybermen invaded Telos and took over the refrigeration and converted it into their cyber-tombs to use for suspended animation. They also attempted to wipe out the Cryons, but some survived, unknown to the Cybermen. These were able to contact Lytton in order to hire him. They kept a secret base under Cyber-Control but it is unclear whether or not they survived Control's destruction. (DW: Attack of the Cybermen)