Arcateenians were made mostly of liquid, (TV: Cyberwoman) yet adopted a humanoid form. To maintain their shape on any planet with a stronger gravitational field than their own, they required large amounts of energy. Their internal structure could be seen faintly through their skin. They had tendril "hair" on the top of their head and on their backs. They had five long, slender fingers and a blue tint to their skin. Some Arcateenians had wings and could fly. (TV: Greeks Bearing Gifts, Invasion of the Bane)