Vissians were distinguishable by crescent-shaped, segmented ridges circling the eye at the temple. Unusually (by Human standards) the Vissians had three genders: male, female, and cogenitor. The third gender, cogenitors, made up only 3% of the population and were treated as inferior, existing only for facilitating reproduction between males and females.
Vissians were able to read, learn, and retain large amounts of new information much more quickly and easily than Humans.
History and technology
At least one ship type was capable of withstanding temperatures higher than 11,000 degrees to withstand exploration within a stellar corona. Their stratopods were able to pass through the hydrogen layer of a hypergiant.
Culture and philosophy
Vissian appreciation of food was based on aroma rather than taste. Of Human foods tried, they tended to like varieties of cheese.
Vissians were more forward and liberal than Humans were with regards to copulating. They preferred to have sexual intercourse first before continuing a relationship.
Vissians tended not to travel far, believing that there was sufficient exploration close to their homeworld: this is the reason why they had not expanded particularly far from their homeworld, despite possessing warp drive far longer than Humans had. Their primary goal was to meet new species. They were willing to share their technology with the Enterprise.
In the ebook The Future Begins, there was a Vissian woman serving in the Starfleet Corps of Engineers in the 24th century.