The Lenarians are barely visible beings who appeared to most other species as shadows, re-enforcing the misconception that they were chameleon-like beings or "living shadows". The Lenarians are from Lenar a large, high-gravity, seldom-visited world orbiting the ultraviolet supergiant Ka'Dedus. Since Lenar had no ozone layer, ultraviolet light passed freely to the surface, while other light wavelengths were mostly blocked by the heavy gases in the planet's atmosphere. Thus, all lifeforms on Lenar could see in ultraviolet light ranges, but were blinded by all but the dimmest light in other wavelengths. This is why Lenarians normally wear a visor when they left Lenar, and expected to be exposed to daylight at their destination. Compared to other species, they could see exceptionally well in the dark.
The Lenarians are short, stocky beings, averaging 1.3 meters tall and nearly as wide. Though they were nearly invisible in normal light, Defel were actually colorful beings. Viewed under ultraviolet light, their fur appeared in colors ranging from yellow to blue. Their snouts appeared green, with orange, gill-like slits at the base of their jawlines. Elderly Lenarians lost their ability to absorb light, fading to a dull dark brown under visible light.