The phrase oxygen breathers described species whose bodily functions depended on the consumption of oxygen sourced from the ambient air. Should these organisms fail to acquire sufficient oxygen, they would experience hypoxia, leading to loss of consciousness and ultimately death. As an example, humans were classified as oxygen breathers. Conversely, Gand, Kel Dors, Morseerians, and Skakoans represented examples of beings that did not rely on oxygen.