Prior to stardate3018, several mapping expeditions had revealed no indigenous life on the planet. The atmosphere was capable of supporting humanoid lifeforms.
In 2267, the ornithoid lifeforms, from outside the Milky Way Galaxy, Sylvia and Korob established an outpost there for the purpose of learning about the worlds of the Federation. Sylvia became infatuated with sensation, and dangerously irrational. To stop her, James T. Kirk destroyed the transmuter used by the aliens. Without its power, the two aliens were not able to survive on the surface of Pyris VII and died. (TOS: "Catspaw")
The original appearance of Pyris VII was replaced when the episode "Catspaw" was remastered in 2006. Additionally, a new matte was created to represent the castle located on the planet, using the original shot of the fog-shrouded entryway and building the full castle on top of it.
In "The Explored Galaxy" star chart, Pyris VII (misspelled as "Pyrix VII") was located between the Tholian Assembly and Romulus. Both were identified in DS9: "Call to Arms" as being located in the Alpha Quadrant. According to Star Trek Maps (page 29), Pyris was a blue dwarf star with ten planets.