Doboids
-Homeworld: Aethera.
-Group: Mollusca (cephallopoda subgroup).
-Average height, weight and lifespan: 7 feet, 180 pounds, 400 years.
-Species traits: all members of this species are capable of using psionics, and are also quite intelligent, and quite traditional, but overall physically frail and weak (although individuals can vary), their weakness forces them to use 'serf' species and slaves for heavy work, and their population growth is stunted due to both their slow reproduction speed and the War. Their sense of hearing is also rather poor, but that's not a problem for a species that can use telepathy.
-Total population: 40 billion.
-Caste: religious leaders, academics, politic.
-Racial slurs: squidfaces, squids, octopus, mind flayers, brain suckers, squiggies, parasites.
As one of the four member species (and the other half with all power), doboids are officially the highest echelon of the Hegemony, being its religious leaders and politics, and most psionics able to kill are also doboids. Most are somewhat zealous of the religion the Hegemony was built upon and petulant, and will force any non-hegemonic sophont in their presence to join their empire, either through evangelization or through the force of arms, and if that fails, they will enslave them; if that fails too, they'll do anything to kill the sophont, mostly in the form of either psionic blasts or loc-hanae troopers.

Loc-hanae
-Homeworld: Kilrados.
-Group: Felidae.
-Average height, weight and lifespan: 7 feet, 250 pounds, 180 years.
-Species traits: loc-hanae are physicall powerful, nowhere as near as therawyrms nor the Hegemony's own power houses and 'residents', the wabaks, but still strong enough to deadlift 700 pounds with little difficulty, they're born fighters due to being predators (their sharp teeth and retractable claws have a part on this), and honorable to a fault. On the other hand, they don't take well to any insults to the Hegemony's religion, take insults to their personal honor even worse, and due to the Hegemony's stagnance they take long to adapt to anything.
-Total population: 80 billion.
-Caste: officers, special operations, peacekeeping.
-Racial slurs: furballs, cats, Thundercats, clawhands, furries, kittens, tiggers, Hobbes.
Powerful and zealous, loc-hanae evolved on a savanna planet, Kilrados. These felines are the main fighting force and peacekeepers of the Hegemony, very proud and honorbound to the empire, and also serve as officers for lesser troops and slaves armies and peacekeeping forces, both in the 'Core' systems and worlds conquered by the Hegemony. Their history begins exactly when they found, fought and evetually joined the doboids, so anything before the 'Birth of the Holy Hegemony' is a mystery, since the loc-hanae destroyed every bit of history that came before the event.

Naurits
-Homeworld: Tuanda.
-Group: Arthropoda.
-Average height, weight and lifespan: 5 feet, 130 pounds, 120 years.
-Species traits: naurits adapt fast and and have incredible reflexes, which makes them born strikecraft pilots and vessel officers and crew, but they're also disturbing looking even for arthropods, and while still stronger than doboids most other known species outmatch them physically. Plus, their reflexes do not apply with ground vehicles.
-Total population: 40 billion.
b]-Caste: strikecraft pilots, naval officers, crew, merchant navies.
-Racial slurs: crabbies, mandibles, bugs.
The third member species of the Hegemony, and the first to be conquered by the fledging empire, the naurits were conquered by the doboids and the loc-hanae just as they were leaving Early Space Age. Their primitive armies were no match for the superior warships of the alien empire, but rather than wipe them out to the last, the Hegemony conquered them and assimilated them in all aspects of their culture. Despite this, many naurits aren't as religious as their 'betters', probably due to the fact they are also in charge of the merchant fleets of the Hegemony.

Martox
-Home system: none.
-Group: Reptilia (humanoid subgroup).
-Average height, weight and lifespan: 6.5 feet, 150 pounds, 250 years.
-Species traits: charismatic and pleasant to be around even to species not belonging to the Hegemony. On the other hand, they are quite sedentary, meaning most won't leave the planet or station they were born in except in extreme cases, and quite wasteful, and are also the lowest echelon of the Hegemony main species, only higher than the genuine slaves, drifters and wabak. They're also the only one without a system to call home.
-Caste: service sector.
-Racial slurs: nomads, homeless, four-eyes, toothies.
The lowest echelon of the caste system, martox are still part of it, and therefore not slaves. Due to their place in the Hegemony most martox are very pious, if not zealous, but can be just as dangerous if properly motivated.

Another interlude, this time about the 'main' species of the Hegemony. If it looks a bit lacklusting, it's because I'm keeping the real thing of the Hegemony (its religion) for much later. Besides, the 'serfs' interlude will be longer.