Native to Zonda, described by Zen as species Alpha 7/5, "a xerophyte of the genus Corla", which Avon took to mean "a cactus!". They were collected to near-extinction, prized for their partial telepathy and ability to move. They also provided the raw material for the addictive drug shadow. Moon Discs avoided direct sunlight, and kept in the shadows, hence the name of the drug. The Federation, under the guise of the Terra Nostra, harvested Moon Discs on Zonda, supplying them with shade. Some if not all of these plantations were destroyed by Blake in one of Liberator's rare uses of its surface strike capability. Whether this rendered the species truly extinct is unclear: Blake said that it "won't hurt [the President] much, but it'll sting a bit", but this is rather vague. Avon suggested that Moon Discs in the plantations were collected from deep desert. The plantations were protected by the President's personal security force.
Cally, telepathically isolated by the Darkness, was given enough strength by the Moon Discs to overcome her loneliness and deactivate Orac by telekinesis. She took a Moon Disc back with her to Liberator (although she was not seen to be carrying one when she teleported aboard). Moon Discs normally died when taken from their native planet, but Cally told Avon that "you have to talk to them". This specimen was never seen again.