Bwujan

Bwujans were a humanoid species native to Bwuja noted for having gills and residing in an underwater civilization. A few Bwujans were air-breathers who lived on the surface.

Biology and culture
Underwater Bwujans resided in ocean cities more than half a mile beneath the surface. Many wore jewelry made from shells. Priests fostered the superstition that air-breathers would one day threaten the undersea world.

Underwater Bwujans appeared Human except for having two gills on each side of their necks and being able to breathe ocean water. In rare cases, offspring were born without gills. Priests killed these "devil spawn" shortly after birth. Compassion drove parents to leave air-breathing infants on the surface, and rulers such as King Raan XIV left them in air-filled caves where they could be collected by air-breathing adults. Some lived within a network of caverns, while others were able to climb to the surface and live in surface villages. One such community had 58 residents, 14 of whom were born there. In rare cases, air-breathing parents had water-breathing infants. 

History
10,000 years ago, Bwujans were cultured, lived in cities, and had invented telescopes. Scientists first discovered that the path of radioactive debris from a supernova would wash across the surface of their world in three hundred years, incinerating the surface.

Circa 4700 BC, a plan was devised to migrate their civilization deep undersea, their only hope of surviving the disaster. Over the next two centuries, artificial gill transplants were developed based on lizard gills, with many lives lost due to experimentation and their unsophisticated medical science.

Circa 4400 BC, by the time the surface was destroyed, a small portion of the population had migrates, living in the deepest ocean trenches and caves. Ignorant of the mutative properties of radiation, scouts sent to the surface either died or returned near death, and they concluded that the surface was damned.

For the next 1,500 years they continued to survive with gill implants until a natural random mutation produced a child born with gills. The trait was dominant, and passed along over the generations until everyone was born with gills. The people built underwater cities, invented harpoons, built airlocks and submarines, and domesticated Bwujan porpoises for transportation. Another genetic adaptation was telepathic communication

By the 23rd century, radiation had subsided on the surface. In 2266, the Enterprise was assigned to study the current underwater civilization, assessing the changes it endured from having experienced the fastest natural adaptation on record. Temporarily assigned to the ship was Urey University assistant professor Barbara McCoy, a xenobiologist who accompanied Leonard McCoy, James T. Kirk and Spock on the research mission, using comp-ox capsules to breathe. The contact team were identified as air breathers and left in air-filled caverns that led back to the surface. Climbing, they eventually discovered a surface village and the truth of Bwujan genetics. Eventually, water-breathing royalty adopted the water-breathing son of air-breathing parents, while those parents agreed to raise the king and queen's air-breathing son. 

Known individuals

 * Amu
 * Doro
 * Lojo
 * Raan XIV
 * Saya
 * Tako
 * Tako's wife