Esto

Esto was a planet located in Lagoon Nebula.

Flora and fauna
It was home to a species of psychic parasites (PROSE: Number 1, Gallows Gate Road) and a species of telepathic plants that screeched when anyone stood between them, thus disrupting their communication. (TV: "The Unwilling Warriors")

History
The First Doctor and Susan had visited Esto and encountered its telepathic plants. (TV: "The Unwilling Warriors") At some point in its history, Esto was placed under the protection of the Galactic Heritage. (PROSE: The Tomorrow Windows)