The Precursors
A race of sepentoids dating back at least five million years and the various descendants of that race. Archeological evidence suggest a stellar empire that stretched from the Trantorian Empire to the Acceptian Empire in an area commonly called "The Crescent"
The !zzr Archeological Expedition
A !zzr archeological expedition to an old and mostly dead class L world found rodinum tablets engraved with pictographs. These were found amid evidence of ruins of an old precursor race. Armed serpents. High tech. It looks like they abandoned the world, not died out. Natural Rulers of the Galaxy that had an Empire that ruled what they called the Great Crescent. An area that covers from the Acceptian Empire to the Trantorian Empire. The ruins are 1.2 million years old.
The race itself by its own words are just and firm. They ruled with an iron hand of just law. Their system resembled Chinese legalism. Charts found in the ruins indicate that several nodes of jurisprudence existed. The vicinity of Nakoo. The Kaa region, the middle of the Klingon Empire. An area now within the Acceptian Empire. An area within the Bendarri Empire and the Trantorian location.
Records found indicate the planet's ecology was going south. They packed up and over a period of several decades moved our in an orderly fashion. Where and when are not known.
The Wrecked Ship
The USS Crystal City recovered a wrecked ship with Jubextor frozen in sleep tubes. A condition the knowingly admitted was their graves. They knew they were dying and prepared time resistance volumes to explain themselves. With that and what little was recovered from their computers it is believe they were lost near the end of the Great Crescent Empire over a million years ago.
The real prize were the perfectly preserved bodies of the Jubextor themselves. More than enough material and data was recovered to identify the various known Serpertoid races as decedents of these people. Not to mention the cases of half a dozen non-sentient serpantoids found that are the clearest evidence known that sentient life forms can evolved away from sentience given the right conditions.
Known Descendant Species
Jexa
These are a primitive society on the edge of the Trantorian Empire. They are considered prime directive protectorates. Jexa are constrictors. They reproduce like the Koo. Colors and head shape differ. You have everything from iron age to stone age societies.
There is ample evidence of a former technological society including ruined cities. They avoid the ruins as a general behavior. A lot of "homes of the gods" stuff going on. Bad juju to go near them. One tribe makes it a rite of passage to enter the ruins and bring out a useful item. They have lots of trititanium knives and the like. A female is not fit to have her eggs incubated until she does this.
There is a lot of cannibalism going down. One aggressive tribe likes to eat the young of other tribes whole. In nearly all the tribes a female eats her infertile eggs. The USS Crystal City got an up close and personal view of a dishonor killing. The female skinned and eaten. The male carrying her egg has it ripped out of him. Any young are butchered as well. All before she is skinned of course. Iron age tribe with a Hittite like control system. Nice people.
Remote study of the Jexa continues. It has been noted that the ruins are not old enough for the Great Crescent period, mere thousands of years old.
Jubali?
Jubali are something Klingons do not like to talk about. Approaching that world is forbidden on pain of death. From indications found at archeological sites elsewhere that should be the location of a Serpantoid colony world, perhaps even the Serpantoid home world. The Klingon Empire is not impressed and will not allow the planet to be approached.
Kaa
The original slimy ground crawling bad guys. The Kaa are located in The Fulcrum Region, They control a small empire via the basic tools of fear and terror. They don't even like each other much. Sadistic, belligerent, cannibalistic, they take delight in torturing and eating people. They look for fights. Their favorite comeback is "I will eat your eyes." Not the nicest people in the neighborhood.
Kaa are notability flatter than the other Serpantoid races. their cross section is triangular, not square like the Koo or Keth. Kaa double lay their eggs with incubation occurring outside the body. The also lay more than one egg at a time. The eggs are laid female to the male. The male fertilizes and lays the eggs into the nest. Neither parent is particularly parental. Society is male dominated.
The Kaa are feeling increasingly compressed between the massive implacably friendly Federation, the fair but just Bendarri Empire, and the irresistible Empire of the Acceptians. They have not made moves to expand away from this and the reason is not understood.
The Kaa officially deny the Serpentoid decline and evolution theory. They and they alone are fit to rule, bringing themselves up by their own lack of bootstraps. Kaa adherence to fact is noted.
Keth
Keth are located in the Acceptian Empire. They are clients of that political body. They average six to seven meters long and are built on the constrictor model. Keth are live bearers with the female carrying the child. They have evolved away from the male incubation model. It is noted with the discovery of Jubextor bodies that Keth are the only Serpantoids that have retained the spines. If anything they are larger.
The scholar serpents have been part of the Empire for only 200 years. The Acceptians found them in a peaceful preindustrial society. Or rather a post industrial society. Signs that thousands of years ago the Keth had been a space going culture were everywhere and largely ignored.
The Keth have been quietly accepting of the Acceptian presence. They do find that the ability to get around the Empire is useful to their studies, so they aid those that provide the means.
Koo
Koo are 6 meter constrictor style snakes with small arms about 0.6 meters from their heads. They have no shoulders. Koo are carnivores. The Koo have an interesting reproductive biology in that the females lay the eggs into the belly pouch of the male, who fertilizes the egg, dissolves the shell and carries the young to term. The females are the fathers, and the males are the mothers.
Koo are located in the Federation Far Sector They have developed from a snake eat snake society to one that aggressively seeks mutual benefit. They are Federation members. Koo participate heavily in Starfleet. They are the first Serpentoid race to do so and adjustments have been interesting.
The Koo are one of the chief drivers into the research on the Jubextor. The are interested in their past and the other species they are related to. Seeking benefit for all involved.
Pythonomo
So called "Magical Serpents". The are located spin ward of the Vargr. Pythonomo are marked by large size compared to other Serpentoids being nine to ten meters long. Their arms are close to vestigial, Pythonomo are highly psionic averaging 80 on the Kraith Scale. They run their technological society by controlling a sub-sentient species that looks like a humanoid mole.
When encountered the Pythonomo were of the opinion that any non-psionic species was not sentient. The definition of sophant beings and other matters are bring discussed with them. When encountered they were being used by the Zhodani to "control" the Vargr, as much as you can control the Vargr. That relationship has been damaged.
Joking with the Pythonomo about Spam or Dead Parrots is strongly discouraged.
Sneks
An offshoot from 300,000 years ago currently known only by a few bodies and archeology. It isn pot known if any live examples are extant.
They had an unsuccessful war with a race of Badger furries noted for a willingness to engage in interpersonal violence. The Badgers have maintained a history and awareness of that war, and the Sneks over a period of 300,000 years. An institutional memory unheard of outside of psionic species.