JOVIANS

Planet of Origin: Jupiter

The Jovians are a sentient species that built several advanced arrogant civilisations on their planet which, given the size of the planet, have not all made contact with one another. Although  their technical science is on pair with that of Humanity, their knowledge of astronomy is lcose to nil, as they know about the existence of the sun and the four Galilean moons of Jupiter, but are ignorant over all other celestial bodies.

They are built around radial symmetry with  tentacles and sensory organs allowing them to detect mass. Substances of low specific mass are transparent to them, allowing to see through the dense Jovian atmosphere as well as Humans see through Earth air. Oxygen is lethal to them, and they may drown if submerged in ammonia, which is known to form lakes in the vast islands where they built their cities. 

For 25 years they had radio contact with Human settlers on Ganymede, but immediately cut contact when they realized  they were dealing with non-Jovians, feeling sudden repulsion and xenophobia. Robots were later sent down to the planet in hopes of restoring contact.

Source: Isaac Asimov, Not Final! (1941), Victory Unintentional (1942) 

LAMBERJ

A non-corporeal energy-based species which has developed a space faring civilisation and is most likely energy-based like the Mizzaretts with whoe they  have a commercial rivality with the Lamberj species.

Source: Isaac Asimov, Buy Jupiter!

MIZZARETTS

A non-corporeal energy-based species which inhabits inhabit the coronal haloes of O-spectra

stars and has developed a space faring civilisation, travelling the cosmos in field-enclosure ships. When encountering corporeal species, they usually use encounter suits aka Simulacrons which are tailored to look like a divine or idealised version of the species they interact with. When meeting humans, they look like golden greek gods, but act very mundanely.

Mizzarett have a commercial rivality with the Lamberj species. They are known to have colonies on Kimmonoshek.

Source: Isaac Asimov, Buy Jupiter!

KLOROS

The Kloros are a chlorine-breathing, colonial insectoid species which developed an expansionnist space faring civilisation. They resemble man-size insects with a number of small tentacles protruding from their chest, a long, slender neck and a diminutive head containing a somewhat triangular-shaped proboscis and a pair of huge bug eyes. Their central nervous system brain is located in the abdominal region, and their head acts mainly as a support for the sensory organs. Their blood is green. Oxygen is deadly for them.

Kloros  have a respectable sense of morale. They lack the concept of familial bond, but do have an analogous "group bond" to their colony and always travel with their groups.

Source: Isaac Asimov, C-Chute (first published in the pulp sci-fi magazine Galaxy in 1951 and  later published in the book Nightfall and Other Stories).

MAUVS / MAUVIANS

The Mauvs are a large humanoid species which developed an industrial civilisation that ended  in a nuclear war. The survivors were rescued by the Hurrians who had bee nmonitoring them. They helped them rebuild their world, instituting a eugenics selection program to make the Mauvian species more docile. The Mauv were unable to pay for the Hurrians' service as their world had been rendered resourceless by the war and the whole species, forced to pay in servitude, rather than material goods, became slaves to the Hurrians.

The Mauvs have thinly-haired bodies, coarse-featured faces, broad noses and flat cheekbones. There appearance contrasts with their submissive nature, as they never question authority, and never disobey orders from the Hurrians.

Source: Isaac Asimov, The Gentle Vultures, by Isaac Asimov (1957)

HURRIANS

Planet of Origin: Hurria

The Hurrians are a sentient species which had developed a non-competitive interstellar empire as of the late 19th century. 

They generally look like an Earth's monkeys, with long thin arms and stubby tails, standing about a meter tall, with black skin covered in dense fur, and a mobile nose on their faces. They evolved from small primates, rather than apes, are vegetarian and mostly non-competitive. They abhor the idea of violence and war, and have accepted as fact that all other species end up destroying their own civilizations after discovering nuclear power. Thus, rather  trying to interfere in their warfare or prevent them. they developed a policy of monitoring other civilizations from distance, waiting  to come down and help the survivors build a new civilization, genetically altering them to remove their competitive impulses and making them subjects to the Hurrian empire.

Although they describe these actions as righteous and helpful, the Hurrians benefit of the removal of competition which ensures their status as the dominant power of the galaxy and make each species pay for the help received in one form or another.  They are known to have aided the Mauvs in such a manner. 

Source:  Isaac Asimov, The Gentle Vultures(1957)

VENUSIANS / PHIBS / CENTOSAURS

Planet of origin: Venus

Phibs are a peaceful green skinned amphibian humanoid species with wide set goggle eyes, broad lipless and mouth, muscular webbed arms living in apreinustrial tribal society in the highlands lakes of Venus.  They communicate via touch-based telepathy and  suckle their own. They have been known to take momentary telepathic control of less evolved indigenous lifeforms such as the twenty-legged two hundred tons serpentine bodied monsters called centosaurs for self-defense.

Note: Phibs look much like the version of the venusians Frank R. Paul's Painted the same year.

Source: Isaac Asimov, Half-breeds on Venus.

MARTIANS / TWEENIES / HALF-BREEDS

Planet of Origin: Mars

Martians are a humanoid species living on Mars which is genetically and socially compatible with Earth's humans but which possess "cold, analytical reasoning powers" but lack the "emotional drive and boundless energy of the Earthman". 

After mankind began to travel to the red planet, tweenies - Half-human half-martians half-breeds - started being born (see picture). Thet weren't accepted on Mars and so had to be brought back to Earth where they were being taken care of by social services. mainly in asylums. Tweenies are generally more intelligent than humans or martians but look like normal humans with a "brush of wiry, dead-white hair that rose stiffly in all directions like porcupine-quills".

Note: Martians are actually never met in the stories conerning Tweenies but are believed to be human-looking as the stories tell of more than a thousand tweenies are known to have been born, so inter-species unions must have been somehow not against nature, although no details are given on that matter.

Source: Isaac Asimov, The Half-Breed, Half-Breeds on Venus