Cryon

The Cryons were a crystalline 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 moved slowly and had echoing voices. Due to their unusual composition, they could not survive temperatures above freezing and would steam and boil when subjected to heat. (TV: Attack of the Cybermen)

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

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

The Sixth Doctor kept a Cryon pendant in his C chest. (AUDIO: The Carrionite Curse)