The arrival of protogenos marked the start of the Protogenocian Era, a billion-year-long era that, like Earth’s Archean Eon, saw the emergence of the truly first complex life on the planet. Much like Earth’s early microbial world, where cyanobacteria pioneered photosynthesis and laid the foundation for future life, Atmos’s biosphere was shaped by the metabolic innovations of its first major life forms. Towards the end of the Protogenocian, from their ancestor protogenos, two dominant lineages emerged, Heterotrophis (Whole Producers) and Autotrophis (Self Producers). The autotrophs produced their own food via photosynthesis and/or chemosynthesis, and the heterotrophs obtained energy by eating the autotrophs and other heterotrophs. Competition between and within these clades would, over hundreds of millions of years, result in an explosion of biodiversity on Atmos. 

Heterotrophs and Autotrophs

Autotrophs

Autotrophy is a term used to describe organisms which have the ability to produce their own food from inorganic substances. The most common form of autotrophy is photosynthesis, where plants, algae, and some bacteria convert sunlight, carbon dioxide, and water into glucose and oxygen. Other autotrophs employ chemosynthesis, a process that uses energy derived from chemical reactions involving inorganic molecules, such as hydrogen sulfide or methane. Autotrophs are essential to a sustainable ecosystem and will generally serve as the base of any food web.

On Atmos, Autotrophis evolved the ability to harness energy directly from its environment, either through photosynthesis, using light from Phanes, or through chemosynthesis, drawing chemical energy from hydrothermal vents and mineral-rich waters. These early autotrophs transformed Atmos’s atmosphere and oceans, releasing oxygen as a byproduct and altering the planet’s chemistry in ways that would enable further biological advancements.

Cyanophytis

On Earth, most photosynthetic organisms employ green pigments, such as chlorophyll, to harness the sun’s energy efficiently. Because Atmos's sun Phanes, emits most of its light in the blue wavelength, autotrophs with blue pigmentation-similar to Earth’s blue-green cyanobacteria-eventually grew to dominate. Rather than relying on green pigments like chlorophyll, Atmos’s dominant autotrophs developed blue pigmentation, similar in some ways to Earth’s cyanobacteria. These pigments allow them to efficiently capture and utilize the available light spectrum, giving them a significant competitive edge over other autotrophs. Over time, these blue-pigmented organisms, collectively known as Cyanophytis (Blue Plants), became the foundation of Atmos’s biosphere. Meanwhile, other photosynthetic lineages with less efficient pigmentation were outcompeted, surviving only in microscopic or highly specialized niches.

Cyanophytes are primarily asexual reproducers, propagating through fragmentation, where a portion of the organism breaks off and continues to grow independently. However, many species also reproduce sexually through the production of hormogonia-short filaments of specialized cells that detach from the main organism. These motile structures help cyanophytes colonize new areas, drifting through the ocean currents until they settle in a suitable location. Over millions of years, this reproductive flexibility has allowed cyanophytes to diversify into an astonishing array of forms, from free-floating planktonic species to towering benthic structures that dominate the ocean floor. While thousands of species emerged from these basal cyanophytes, two clades ultimately proved to be the most successful.

Cyanorezis

Cyanorezis (Blue Roots) are one successful descendant of the cyanophytes. An early algal offshoot of the basal cyanophytes, the cyanoreza have developed simple root-like holdfast structures to anchor themselves to substrates, such as rocks or aquatic plants. These photosynthesizers come in many shapes and sizes, yet all possess colonial tendencies, their gelatinous forms embedding together in a mucilaginous matrix, providing structural integrity and protection against environmental stress. The cyanoreza are often seen clumped together, forming massive algal blooms throughout Atmos’ oceans. 

Cyanocomis

Cyanocomis (Blue Hairs) is another successful descendant of the cyanophytes. Representing a specialized branch of the cyanophytes, these organisms have developed elongated, hair-like structures to maximize their surface area, allowing them to capture more light from Phanes. In addition to their increased photosynthetic efficiency, some cyanocoma species exhibit a unique behavior where their filaments intertwine, providing mutual structural support and forming dense mats. 

Heterotrophs

Heterotrophy is a term used to describe organisms which, unlike autotrophs, lack the ability to produce their own food. Heterotrophic organisms obtain energy by consuming organic matter, either from other living beings or from the decaying remains of once-living organisms. Unlike autotrophs, which produce their own energy through photosynthesis or chemosynthesis, heterotrophs consume other organisms-whether living, dead, or decaying-to meet their metabolic needs. On Earth, this category includes everything from bacteria and fungi that decompose organic material, to megafaunal herbivores and predators.

On Atmos, Heterotrophis evolved as consumers, deriving energy by consuming autotrophs or preying upon other heterotrophs. Some early heterotrophs adapted to a scavenging lifestyle, breaking down organic debris and recycling nutrients within the environment. Others evolved into active predators, developing mobility, sensory adaptations, and specialized feeding structures to hunt their prey more efficiently. On Atmos, the dominant heterotroph clades diverged into what were initially a sessile clade and a motile clade. The sessile clade absorbed food through their skin, similar to a hagfish, whereas the motile clade opted to use a mouth to take in nutrients. 

Membranutrioris

Membranutrioris (Skin Feeders) is a clade of hetrotrophs which adopted a sessile or slow-moving lifestyle, anchoring themselves to surfaces such as rocks, seafloor sediments, or floating structures. Their primary method of nutrient intake relies on a specialized semi-permeable membrane, which absorbs dissolved organic matter, microscopic detritus, and even small microbial life directly from the surrounding water. To maximize efficiency, many species develop increased surface area, forming fan-like, fronded, or ribbon-like structures to enhance nutrient uptake.

Luranutrioris

Luranutrioris (Mouth Feeders) represent the more mobile and actively consuming branch of the heterotrophs. Unlike their sessile relatives the membranutriors, these organisms develop specialized oral openings to ingest food directly, allowing for greater efficiency in acquiring nutrients. Early luranutriors began as simple, soft-bodied scavengers, consuming organic detritus, microbial life floating in the water, autotrophs, and even other heterotrophs, eventually growing in complexity and occupying increasingly varied niches.

The interplay between autotrophs and heterotrophs fueled an ecological arms race, driving evolutionary innovation on both sides. Through this struggle, Atmos’s ecosystems became increasingly complex, paving the way for higher-order food webs and, eventually, the emergence of even more advanced life forms. This exponential increase in complexity would, over millions of years, lead Atmos into its next era.

Continue on to the evolution of Atmos's higher order life forms, in the Thalassian...