- This page features the planet Edos; it is possible you may also be looking for the Edo species.
Edos was the homeworld of the Edosian species, as well as the Edosian orchid; Edosian slug and Edosian suckerfish. (DS9: "Broken Link"; ENT: "These Are the Voyages...")
Background
Edos is the name of the homeworld of The Animated Series's Lt. Arex, as given in a biography published in a 1974 Lincoln Enterprises catalog. The biography notes that Edos is not a Federation member despite Arex being a Starfleet officer. It also notes that Edos lies in the Triangulum constellation, which lies at the edge of the Milky Way Galaxy, near the galactic barrier.
Information from the Lincoln biography is not strictly canon, though the name of the planet seems to have been accepted in canon. See the full text of Arex's biography at Curt Danhauser's animated Star Trek site.