See also: The Edo, a humanoid species native to Rubicun III.

The Edosians (sometimes Edoans) are a race native to planet Edos in the Alpha Quadrant. They bear some physical resemblance to Triexians, though Edosians are considered a more animated race. (NF short story: "The Road to Edos")

Arex was identified as an Edoan in Alan Dean Foster's Star Trek Logs novelizations, based on never-aired background information from TAS. That he was actually a Triexian was established in the New Frontier series, and the root of the confusion touched upon in "The Road to Edos."