The home planet of the peaceful Antosians, who healed the maimed Fleet Captain Garth of Izar by teaching him cellular metamorphosis, a gift he then turned against them.
Antos IV is the home of the Antosians, a gentle people who have mastered cellular metamorphosis, the ability to repair and reshape the body by will alone. Its story is told in the Original Series episode Whom Gods Destroy.
When the celebrated Starfleet officer Garth of Izar was terribly injured, the Antosians nursed him and taught him their technique so that he could heal himself. The process, or the injuries, left him insane. He ordered his crew to destroy the planet, and they mutinied rather than obey. Garth was confined to the asylum on Elba II, where he used his new shape-changing skill to impersonate others.
The planet is also mentioned in Who Mourns for Adonais?, in which Chekov refers to a giant energy-generating dry-worm found there.