Cryons are a species from their homeplanet of Telos.
The Cryons are humanoids. Their bodies are clear as if they were made of glass. In order to survive, a Cryon needs to be in a cold climate.
Cryons lived on the cold surface of Telos until the planet started to warm. To escape the heat, they moved underground and built huge cities which would keep them cool. However, the Cybermen arrived to take control of Telos, taking the cities from the Cryons to be used as tombs to keep Cybermen in suspended animation.