Pretty cool heinleinfan... I tend to use earthlike concepts for standardisation for reasons that suit the creation of universe i created but other time i just go out there?
Good stories are about human interactions. You can think up all the alien races you want, but the story should be about how human beings are affected by them, of affect them, rather than about the alien races only. People understand stories about the unknown better when a human being is experiencing that unknown. Space opera style often tries to make the alien races too human, in which case it would usually be better just to write about human beings with strange cultures. I'm sorry if I sound like I'm narrow-minded about space opera; that's not the intention. But I tend to think that a story best describes an alien race when it is humans interacting with a single species of alien life or multiple ones that are actually related. This is especially important in short fiction, when too much clutters it up. Otherwise you need a good reason for so many species to be put together, in which case the story probably isn't focused on all the accumulated species.
But many writers who try that end up making the aliens too human, in which case it's better just to use humans in a sci-fi setting rather than an uncreative alien race.
A genetically engineered organism, from an ancient and unknown species. Female, with tetra-helic dna that is a mix of carbon and silicone. Two hearts, carbon nano-tube woven endosekeleton with infused with cobalt for a little extra durability. No reproductive organs, but can have sex. A biological quantum computer for a brain, though she is forced to learn as she has been in relative isolation. Can control nerve responses to pain to a high degree. Has pale blue skin that is like a living rubber membrane, as well as hair that is bright white(though it gets shaved off when she joins the service). She has four legs, and long slender hands and fingers that seem a bit large for her small stature. Eyes that are 50% larger than Terran (human) eyes, and are azure blue. Learns new skills in hours or days depending on how difficult they are. Approximate age between 500-1000 years. Can consume basically anything organic (with in reasonability). Immune to a vast amount of illnesses. Despite that she is not immortal, and can be killed, or die of extreme old age. Though the genetic make up slows the process considerably aging wise. 1.75 meters tall, and weighs 61.23 kilos. She may be considerably small compared to the average Centuria that tower over her at 2.16 meters or taller, and 123.83 kilos etc. She can be a vicious little thing when need be. Having been labeled a monster in her own rite as she use to be a very nasty interrogator on neutral grounds between a host of races. She is working to put that behind her finding a new life that is less grotesque. I have a few more, but they are not as complicated. That and Terrans are self explanatory as we all are Terrans.
