Lamidav
The Lamidavians (or, as they call themselves, the Leminam), are the first contacted extraterrestrial civilisation. They were discovered in 2034, by HMS Beagle, in what is now part of the Empire's sphere of influence.The Lamidavians are an advanced civilisation with technology in many areas greater than our own, but had the misfortune to not have discovered hyperspace independently. Both the Lamidavians and the Empire to which they are now aligned have taken great pleasure in cooperating.
Biologically, Lamidavian life appears to have had a different abiogenesis to Earth life, as while they have structures which are analagous to our DNA and cell machinery, this differs in fundamental ways from the common ancestor of even an Earth tree and a pigeon. Human and Lamidavian food is very different, but alcohol has a similar effect on both species, which has been the source of much cultural interchange.
While our friends have been happy to open upon their textbooks in many areas, Lamidavian reproduction remains somewhat of a mystery. It is considered polite not to ask why nobody has ever seen a child of the species.
Appearancewise, they have rigid external skins (these are often called exoskeletons but this is technically incorrect as they are not primarily structural), which they decorate by affixing materials or patterns in various permanent or less permanent fashions. Body symmetry is complex but can largely be understood as a mix between twofold and threefold. If you imagine a giant bug, you're not that far off.
The primary Lamidavian language (which they call "Lamidav") is pronounceable, very crudely, by humans, but has grammatical constructs that elude all but the keenest learners. Happily, many of them have learned English!