Arvaisans

The Arvaisans are an offshoot of Humanity that developed thousands of years ago as a result of the needs of survival. Arvaisans originally stemmed from the system of Arvasine. They traveled there in the early years of galactic exploration and set up a colony named after the starship that they lived on. Today the Arvasine system is recognized as one of the systems in the Andromeda trifecta of Xorasine, Arvasine, and Metadovolsine.
When the Sol Confederation colony fleet reached Andromeda, they already had a set destination of three systems close to the core of Andromeda. A prime spot for research and exploration as well as three possibly habitable systems. While the other two systems were relatively safe and habitable, the Arvasine fleet arrived in the system to find out that it was nothing but barren rocks, except for an ocean world that they creatively named Arvasine Prime. Arvasine Prime (or just AP) had a stable nitrogen-oxygen atmosphere, but the whole world was populated by a deadly bioluminescent microorganism species that would be almost certain death for anyone that was infected by it. Their ships were dangerously low on supplies and oxygen though, so they had no choice but to protect themselves in any way that they could. They took apart their ships to use as reinforced habitats, built more advanced medical technology, and research ways to combat the infections any way they could. By deconstructing their ships they had cut off any means of communication with the other colonies, and so they were presumed as dead.
Nearly six hundred years later the colony was rediscovered by an exploration fleet, now after the first contact with Telvins. The fleet found a long lost colony of Human origin of people who lived on an ocean world with a strange symbiotic relationship with an otherwise deadly microorganism. The people, now regarded as their own distinct species, had genetically engineered themselves to become more and more adapted with the microorganisms until they could not exist without each other.
Because of the hundreds of years of genetic engineering to cope with living on an ocean world full of deadly microorganisms and little resources, Arvaisan physiology has become quite different from Humans. The most prominent difference is the two to three membrane encased ridges embedded on their back, which glow brightly due to the colonies of microorganisms that live inside them. The Arvaisan microorganisms produce food via chemosynthesis that provides important nutrients to the Arvaisan body. The microorganisms also siphon chemicals from the body that may not provide any benefit or are harmful to Arvaisan, but are vital for the microorganisms. Arvasians are able to hold their breath for a very long time because the microorganisms inside their lung tissue use carbon dioxide and give off oxygen in their chemosynthesis process. Arvasians are statistically stronger and faster than normal Humans, although this may be attributed to their very active lifestyle and survivalist culture.
Nowadays Arvaisans make up around 2% of the total intergalactic population. Their culture is unique with serious utilitarian ways of doing things. They have not fully rejoined the Sol Confederation but have become a mostly autonomous protectorate, meaning they still make their almost all of their own laws and have their own capital and government, but their military is one and the same with the Sol Confederation military forces. They are also heavily tied with the Sol Confederations economy and people born in the Arvaisan unincorporated zone are automatically also Sol Confederation citizens.