These are the blue-green marbles, the gems of the Galaxy. From a simple visual identification, it can be deduced that these worlds will have thriving biospheres with a long and rich evolutionary history. Oceanic cover ranges between 50 and 85%. Intelligence may even develop on such planets. Of course, the trace biochemical make up of these worlds might be incompatible with Earth life, or there may be other factors that make such planets marginally or completely uninhabitable. Regardless, taken as a singular, EuGaian worlds are Edens in the stark desolation of space. Example; Earth Eugaian worlds have fully developed geological, hydrological, and biological systems. Life is usually quite diverse, although there may be cases where evolution beyond simple microbial forms never occurred, simply because there was no environmental pressure to do so or because insufficient time has passed since the planet's formation or since some cataclysmic extinction. However, even in these cases, the life present produces oxygen and carbon dioxide as a byproduct, making the atmosphere unique and generally friendly for non-native life forms. In short, these are the archetypical "blue marbles" that are so covetously sought after by Humankind.
GaianXeric Subdivision These are warm and dry EuGaian worlds, with 15% or less of the surface covered by standing water. Major desert zones are common, and life tends to remain close to the small ocean and sea basins. Plate tectonics are present, but the relative scarcity of water means that this geological process moves slowly. Less water also means that less carbon dioxide is absorbed and locked away into carbonate rock; as such, the atmospheres are carbon dioxide rich and contribute to the over all higher temperatures of the worlds.
GaianCampian Subdivision These are EuGaian worlds with 30 to 50% water coverage, their oceans and seas tending to be quite saline. Climatic extremes are common, and vast inland deserts are not uncommon. Due to the low water table, biomass and atmospheric oxygen is much lower in levels than with other Gaian worlds. The effective absence of an efficient oceanic heat transfer system makes for large temperature differences between the latitudes.
GaianPaludial Subdivision These are EuGaian worlds with 30 to 50% water coverage, where land features tend to have low surface relief, forming extensive swamplands, lakes, lushly forested regions, and semi-open woodland. The climate is predominantly oceanic, with relatively open ocean flow and freedom for globe-spanning weather systems to keep a largely homogenous planetary temperature. Polar regions do tend towards glaciation, however. The geographical arrangement is typically due to a decrease in geological activity, and tends to be common for lower mass, older Gaian worlds.
GaianContinental Subdivision These are EuGaian worlds with 50 to 80% water coverage, with most of the planet's water concentrated within deep ocean basins. The arrangement of continental plates can create a wide variety of climatic conditions across the globe, and these conditions change constantly as the plates continue to slowly drift over the billions of years of the planet's lifetime.
GaianPelagic Subdivision These are EuGaian worlds with over 80% water coverage, the continental plates largely submerged. The global climate is even and tends towards the temperate, although various circumstances can swing that climate to either the cold or the hot end of the spectrum. The majority of the terrestrial regions are islands or micro-continents located along rift or convergent zones.
NeoGaian subtype (informal) Many worlds which currently have Earth-like or EuGaian conditions are the result of terraformation. Only a fraction of terraformed worlds will retain a EuGaian status without constant environmental adjustment; most will gradually become inhospitable as they lose atmosphere, volatiles or develop an unstable climate. Worlds of this kind which cannot maintain homeostasis are labeled NeoGaian.