Characteristics and history
- TOS episode: "The Omega Glory"
- ST references: Star Fleet Medical Reference Manual, Star Charts
- TNG episodes: "When the Bough Breaks", "Suddenly Human", "Rascals"
- DS9 episode: "Visionary"
- TOS novels: The Vulcan Treasure, Crossroad, Across the Universe
- TNG novel: The Forgotten War
- DS9 novel: Devil in the Sky
- TTN novel: Over a Torrent Sea