Calufrax

Calufrax was one of the planets captured by Zanak and reduced to a trophy the size of a football. Its metricized structure, having a variable atomic weight, betrayed its origin as, not a natural planet, but the second segment of the Key to Time, and was recovered by the Doctor and Romana. (DW: The Pirate Planet).

A possibly related planet, Callufrax Minor, was later stolen and taken to the Medusa Cascade (DW: The Stolen Earth).