Holox is a planet with a hostile surface and a rare inner sun instead of a traditional core. Therefore most of its wildlife exists beneath the surface, most notably the Bilgen Bugs.
Most Zotaxians fled to Holox from their home planet of Zotax after a war with their cruel leader. They were unable to survive on the surface and were forced to burrow underground, where they used Voltstones to harvest the energy of the inner sun.