The Ptarians (Official Denomination: Homo Coelus)are the descendants of the Human settlers to the planet Raugaurde, an old world with highly evolved native life. Much of the planet is hot and humid, with dangerously high levels of oxygen. The are in some ways more alien than many alien species in appearance and psychology, due to their mixed heritage.
The Ptarians are exceptionally tall as an offshoot of humanity, being about 200 to 230 cm in height, with exceptionally pale skin, ranging from pale green to translucent, and with reptilian eyes. They are exceptionally strong and have excellent reflexes due to pressures from their environment and the need to survive on one of the most dangerous ecosystems in the galaxy. Their culture requires them to engage in exploration during their youth, which means that most encountered outside of their home system are juveniles, though it should be noted that their maturation is very slow, so that they reach adulthood at the age of 37 Terran years, with a total lifespan of about 180.
The Ptarians have a very complex biology as they are a mixture of Humans and the native species of Raugaurde. While no survivors were found, the dead were found preserved in underground cities and were used to assist humanity's adaption to the ancient world. This has resulted in their having 52 chromosomes as they also added material from large numbers of other species, both Terran, Raugaurdian and other, which makes them unable to breed with baseline Humans.
Apart from their odd skin-tone, which comes from the Rauguardian ancients, as well as bioluminescent hairs (though only on their head and eyebrows) which they use to communicate amongst themselves in their highly complex language. These hairs also display emotions, especially in youth, though as they grow older they increase their control over it. This bioluminescence is quite faint though, and mostly appears as merely a colour change. Their eyes are also highly adept at low light vision due to the incredibly dark forests which span much of Raugaurde.
Ptarians are not only very tall, at 200-230 cm in height, but also fairly thin at 70-90 kg, though this is partially due to hollow bones and other weight saving methods due to the high gravity of Raugaurde. They are quite muscular, but they have a layer of fat over top of their muscles for insulation, not to protect from cold, but from the high oxygen environment which would cause most Humans to spontaneously combust.
Their complex heritage has made them obligate herbivores, as they become ill if they eat meat or even certain animal byproducts. It is believe that they require cellulose in the food they eat to keep it down, though they will not share the exact reasons behind this. Another thing to note is that they have virtually no sexual dimorphism, only having the primary sexual traits (aka the sex organs), the only real difference is that the females are usually slightly taller and heavier, presumably some remnant of sexual reproduction.
Ptarians have a relatively secretive culture. It is known that they lack any sexual interests and reproduce through the use of cloning banks. It is also known that the raise children as a community function, but with an individual taking the primary role. It is also known that they send out their youths to explore the galaxy and study it. Apart from this, little is known for sure about their culture, though they do export technology from time to time.
-Ptarians have genes from a sentient race which they found on Raugaurde
-Ptarians utilize an advanced cloning technology to gain immortality
-Ptarians are able to photosynthesize in their skin
-Ptarians rejuvenate like certain forms of jellyfish
-Ptarians travel out to the galaxy to sample genetics from other races and incorporate them
-Ptarians believe themselves superior to all other sentients
-Ptarians do not in fact have Human ancestory, but are the natives of Raugaurde who slayed the Human settlers and now impersonate them
-Ptarians are plotting to conquer the galaxy, and have been working to turn themselves into the perfect soldiers
-Ptarians can hollow out worlds, or create world shells from the left over material
-Ptarians have slowly been releasing a virus that will wipe out humanity when the time comes
*Note* most of these rumours are considered wild guessing