Antos IV was the inhabited fourth planet in its star system. This was the homeworld of the Antos IV natives and the energy-controlling species known as the giant dry-worms. This planet had a non-hostile relationship with the Federation. (TOS: "Whom Gods Destroy", "Who Mourns for Adonais?")
Prior to stardate 5718, Captain Garth of Izar suffered an accident in which he was maimed and dying. He was transported to this planet by a Federation starship. As he was being cured, the natives taught him the art of cellular metamorphosis. This medical procedure was used to restore the destroyed parts of a body. After he had regained his health, the captain offered them the galaxy. When they refused his offer, he declared them enemies of the Federation and condemned them to death. Before he could destroy them, the starship crew turned against him. (TOS: "Whom Gods Destroy")
According to Star Trek: Star Charts ("United Federation of Planets I") and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Antos (Kappa Delphini) system was located in the Alpha Quadrant. The primary was a G-class star.