In Errand of Mercy
, Spock described the Organians as, "Pure energy. Pure thought. Totally incorporeal."
, Spock described the Companion as, "Vaguely like a cloud of ionised hydrogen, but with strong erratic electrical impulses" and later added that "a large part of its substance is simple electricity."
In his log in Is There In Truth No Beauty?
Kirk described the Medusans as "formless".