This is not a complete write-up.
Let's explore the winged ungulate. Articulate wingfingers, wyvern-style, grasping talon-hands (kinda ape-like) tipped in small (hooking?) hooves, lean and light body (almost like an exaggerated sighthound). Sharpened, hardened heelspur. Slenderized horse's face, almost like a cross between a fine-boned horse (Arabian) and a mule deer - large pale eyes, flaring nostrils, equine ears, sharpened teeth (omnivore, often mainly scavenger). Immensely strong in striking, but not too much core strength for hauling/carrying heavy things. Various earth-toned colors - thin, smooth pelt that's water-resistant, some fur along the fingerbones and on the thicker parts of the membrane near the knuckles. Long, strong, coily tails. Ethnicity is seen in coloration, as well as facial structure, as well as distribution of fur on the wings. Fairly large - some five feet at the shoulder on average when on all fours or seated - wingspan of some twenty-five feet total (each wing a little longer than nose-to-rump length, which is average of ten for a height of five). Live young, no eggs - like horses. Unusual strength of qki. Small, backwards-pointing horns (an inch or two longer than their ears). Pseudo-manes - a patch of long, coarse hairs sprouting between their ears/horns.
Caste A is the 'worker'. They tend to be larger, stronger, more muscular, and very physically present - they have a certain body-awareness and grace about them. They have a very direct, straightforward approach to things, and they don't hesitate or procrastinate in getting things done. As are hunters, guardians, warriors, workers. They're very solid in mind and personality, believe in knowing one's body and one's physical limitations intimately, believe in constantly working to maintain and improve one's health and physical abilities, and are happiest when moving (though they take pleasure in a well-deserved rest). They don't sit still well and don't handle abstract thought/discussion well unless it's anchored in practical examples/applications. As are quite self-confident (occasionally arrogant) as a result of their self-knowledge and are usually the aggressors in an interspecies showdown (combination of protectiveness and pride). Good ones know themselves explicitly and need no managing, only direction, and are happy serving the people while improving themselves; bad ones can be arrogant, self-centered, anti-authority, scornful of less physical castes, and/or reckless to the point of injury in driving to improve.
Caste B is the 'magician'. This caste started with the physically deformed or handicapped and has expanded slightly to include the very frail, stiff, or otherwise less physically adept. (Physiological reason here - if the body fails to develop into a fully healthy young adult, all that qki that goes into maintaining the body gets funneled towards magical ability. They're unique like that.) Most Bs are healers, but some can go into aggressive or nature magics. Much like As, Bs believe in studying themselves and pushing their limits - they're happy to serve the people while they learn more magic, and the good ones need only direction to be useful, not micromanagement. Many Bs have a slight inferiority complex, due to their bodies, and are the least mentally stable of the castes (due to the inferiority, or possibly the prolonged exposure to magical energy - no one's really sure). Bs are not only self-studies; they have a casual master-apprenticeship way of learning, in which they find an older B who specializes in the kind of magic they want to learn and apprentice themselves to that 'master'. There is no hierarchy of magic, just a sense of competency and experience. Bs can learn any kind of magic they wish - there are no limits - but the social urging is generally on healing magic, at least at some point in the B's studies. Bs are often quiet and submissive (though many become more comfortable and outgoing around other Bs). The good ones apply their energy to studying and perfecting magic in order to compensate for their less-than-perfect bodies, glad to be of equal value and use as people with hale flesh, and happy to find camaraderie in other Bs; the bad ones can be passive-aggressive, resentful/bitter, emotionally or mentally unstable, vengeful, lacking in self-worth or self-confidence, or a self-branded outcast.
Caste C is the 'thinker'. These guys are the managers, leaders, ambassadors/diplomats, and philosophers. They're usually pretty average in physical fitness and build, competent and active without reaching the highs of As. Cs specialize in abstract thought and logic. They observe, analyze, and draw conclusions in a rational, scientific-method manner; they're capable of suspending logic briefly to discuss seeming paradoxes (often in the case of the unseen - religion, spirituality, etc). They are excellent at math, science, and languages - these guys are the linguists who not only learn other tongues fluently but study the very structure of interspecies communications. Cs philosophize extensively, usually centering on social interactions - between individuals, between castes, between ethnicities, and between species. They are the ones who see needs and organize plans to fill them; they direct As and Bs; they run society. Good ones are fully cooperative with other Cs and respectful of As and Bs, eager to think and discover and learn, aware of their place within the population and not too arrogant for it; bad ones can be too arrogant, too big-headed and self-important, uncooperative with other Cs, condescending towards As and Bs, or convinced they've already learned/thought enough and can rest on their laurels on a high perch of awesomeness.
Caste D is no caste at all, but a person who never fully developed into any of the three castes. They still try to fit into society, but usually find themselves unable to do as well with magic as a B, unable to be physically comparable to an A, and unable to think as deeply and quickly as a C. (Physically, they often look similar to Cs in their averageness.) These are only one in five hundred or so whose puberty either never starts or never finishes; they are looked upon with sympathy and compassion, but also a tinge of pity, since they will never belong. Many Ds leave their people to go it alone; many suicide, and many are killed in the attempt to fit in (by circumstance, rarely by peers - As and Bs have somewhat dangerous occupations). Some few Ds don't make the futile attempts to put themselves in a caste and instead try to be well-rounded in all things; some even succeed. Most Ds are malcontent, restless individuals who strive in vain to force themselves to finish developing into one of the niches; they work feverishly and usually die young.
They're arlen(ni).