A Taxonomy of Ultranautic Fauna
Evolution
To understand the taxonomy of living organisms one must first understand the principle of evolution. The progeny of any given creature generally inherits physical traits gained during the lives of both parents up to the point of conception.
For example, a citizen who has consummated his marriage after working as a stoker for fifty years will conceive a child with physical traits useful for stoking, such as rigid arm muscles and heat-tolerant skin.
This principle gave rise to the necessity of a rigid caste system during Man's first years aboard the Submarine and the rise of the Abhumans following the collapse of the First Unified Society.
True humans understand that for a society to succeed, one must not only carry out their social function to the best of their ability and only marry within their profession. In uncivilized or decadent societies in which there is no division of labour, humans typically select for superfluous traits. The grotesque physical appearance of Type 1 and Type 2 abhumans is enough evidence to confirm this, hence the need for strict central governance.
Taxonomy
In the year 302 AL (After Landing) a monk took it upon himself to classify the wildlife of the Dry World. In creating his taxonomic system he learned that all living things fit under two overarching categories.
According to his work, we know that all species descended from land-dwelling life are post-terrestrial and those descended from ocean-dwelling life are post-aquatic.
Those recognizably descended from humans are known as abhumans. Since humans were the most abundant and adaptable animal species aboard Ultranautica, our ancestors diverged the most. Thousands of species
On account of the world being flooded for a million years, all organisms not onboard the submarine Ultranautica adapted to oceanic life, evolving accordingly. When the oceans receded aquatic life diversified into hundreds if not thousands of clades filling up every niche the dry seafloor had to offer.