Medusan
- Appearance: Noncorporeal
- Physical appearance is capable of driving most humanoids crazy due to noncorporeal nature (TOS: "Is There in Truth No Beauty?")
- Homeworld: Visalayan
- As of May 2378, 12 Medusans serve in Starfleet (TNG Novel: A Time to Die)
- All but one serve as navigators on long-range vessels (TNG Novel: A Time to Die)
- Biological notes
- Telepathic species (TOS: "Is There in Truth No Beauty?")
- Innately aware of position in space and time at all times, granting them innate skill at starship navigation (TOS: "Is There in Truth No Beauty?"; TNG Novel: A Time to Be Born, A Time to Die)