The Mu Araen (an exonym) are one of the Elder Species, the three sophont species who were the co-founders of the Empire. The Mu Araen live mostly in the atmosphere of gas giants.
Mu Araen are eusocial organisms, and have many differentiated forms to serve their particular function in a vast colony. A Saturn-sized gas giant may have as few as a thousand individual colonies, each readily visible from orbit and containing hundreds of billions of individual Mu Araen.
It is difficult to precisely define their environmental requirements because Mu Araen colonies are extremely adaptable to variations in environment; their hard requirements are mainly for an appropriate temperature and isolation, and sufficient supplies of the elements needed to sustain them (carbon and nitrogen being usual limiting constituents on the gas planets to which they are not native.) They require special adaptation to survive in an oxidizing atmosphere. They have a carbon-based biochemistry, are photosynthetic, and use ammonia rather than water as a solvent for their enzymes. Like Humans and Biran, they are based on a cellular architecture with long-chain polymers encoding the constituents of enzymes, but their genetic material is a branched rather than a linear structure, with the branching and cross-linking patterns being altered by transcription-factor analogs to control the expression of genes. The Mu Araen genetic 'library' is extremely vast, and some types of caste differentiation involve truncating unnecessary parts; only the reproductive-caste has a complete genetic library.
Not all Mu Araen are sentient; indeed, Mu Araen caste-forms differ widely in intelligence, some serve essentially structural roles in their colony, containing atmosphere, transmitting biochemical power or absorbing sunlight. In a typical mid-sized colony of perhaps 100 billion individuals, there will be only about a million full sophonts of the 'thinking castes' and another four or five million 'analytes', living computers with some degree of intelligence, but no will of their own. There is no one 'queen' of a Mu Araen colony; the thinking castes made decisions by consensus. A colony will usually split if timely consensus is not achieved in an important matter; this is uncommon but seems to be the primary limit on colony size. The thinking caste deliberately curates the genetic library stored in the reproductive caste members, and develops new genetic sequences deliberately. Mu Araen can also build and use more conventional technology, though it is typically highly integrated with their biology.
Psychologically, Mu Araen are very different from Humans and Biran, and show no interest in social or cultural relations with them beyond practically-beneficial trade and transportation. This is quite unlike the relationship between Humans and Biran, whose cultures are very different, but interesting and generally comprehensible to the other. Though the Mu Araen are capable of forming spacecraft and were routinely doing so during the Imperial Era, they were often propagated to new gas planets by Human or Biran interstellar ships. Mu Araen colonies often supported their trade with isotopic separation, mining Helium-3 from their gas-giant homes to trade for chemical nutrients (and occasionally technological items.)