I did an Inktober, but only scanned the stuff now. Sapient alien species sorted by name, mostly having appeared in the written episodes (including the not-uploaded fourth).

Foo'': They have an unnerving way of talking, by widely opening their mouths and then not moving them at all. The two lines at the end of the name indicate a fading sound. Seen in Episode 4 in the form of an annoyed parent trying to get their unruly, window-slapping children under control.
Gthuor: A large heavy-set species renown for their loud voices which they enhance with large throats and hollow, inflatable horns. The males' horns are bigger than the females'. They have a tendency to pick jobs where their volume comes into use. Featured in Episode 2 as a trader in a space station.
Hrrau: A large herbivore expressing themselves predominantly with two flag-like growths on their noses. Known to be able to survive in a high-CO2 atmosphere. Featured in Episode 2 as a security worker on a mining planet where multicellular life wasn't far from its beginning.
Idrath: A large exoskeletal native to Goronoi-2 with a good sense of smell and a strength surprising even for their size at the cost of poor stamina. Since the planet had been asessed as too dangerous to visit due to its large, aggressive predators, the species is virtually unknown in the known galaxy, with only one individual having left the planet. They are not particularly bright opportunists too busy surviving than to form any civilisation, their main concerns being food, avoiding predators and reproduction. Since one of the protagonists is a male and gets drawn often enough, I drew a female for a change, which are bigger, angrier and dumber than the males. The females hold territories in which they and their lanky, quadrupedal offspring live, the latter progressively moving to the territory's rims until they mature. Females will then search for a territory of their own, males will become vagrants on the search for mates. Survival rates are notoriously low.
Im Kpaz: One of the smallest intelligent species from the known galaxy and fairly common. They were on a paleolithic level when discovered and seem to be unable to go beyond it, despite there being customized smaller class spaceships steered by groups of them. Most of the off-world individuals live in space harbours and larger cities, where they hunt syncultural animals and collect growths of photoautotrophs for sustenance and in exchange for favours. Sometimes they are also hired for deliveries or as thieves due to their small size. Since they are unable to speak Unicomlang with their high-pitched, chirping voices and translator devices are too big for them, they rely on living translators to communicate with other species. Briefly mentioned in Episode 2.