ALIMBICS

Planet of Origin: A world in the ALimbic Cluster in the Tetra Galaxy.
The Alimbics are an extinct advanced species which developed an interstellar civilisation. They had an exoskeleton, an enlarged forebrains, a head with a single eye, two arms and three legs. They are thought to have been communicating telepathically to one another.
They were a peaceful race until they were attacked by an unspecified enemy. They rapidly advanced in weapon technology, including bioweaponry and won their peace back but remained ready for future invasions. They also began improving their already powerful minds, developing telepathy, telekinesis, and extradimensional exploration. Then came what they called "The Cancer" or Gorea.I t appeared as a gaseous form but soon took on a physical one, one mimicking that of the Alimbics themselves. The Alimbics' weapons were useless against it, and eventually, it took the weapons into its form and used them against their creators. It drained the life energy from its victims, leaving them as empty husks, while growing more powerful itself. To stop it, eight Alimbic elders came together and created the Seal Sphere. The Alimbic people used the process of essence transference to put their telepathic essences in the Seal Sphere. This enabled them to trap Gorea ans send him to a formless dimension of antimatter called the Infinity Void.
Although extinct, a lor of ruins of their civilisation still exist.
Source: Metroid universe

LUMINOTH

The Luminoth are an ancient technologically advanced bipedal moth-like species which has an intense spiritual fixation with light.
According to their legends, they were "born between the stars," searching for a home planet for a very long time. During their travels, they met the Chozo, and exchanged technologies. They then found the planet Aether which they colonized and made their own in a short time.
At some point in the third millenium, a Phaaze Leviathan crashed onto their planet, carrying extremely high amounts of Phazon. The explosive impactliterally tore the planet in two, creating a second Aether, known as Dark Aether, on which all the Phazon concentrated. On that planet, the beings known as the Ing thrived. They found portals to Aether and invaded it. After a nearly a century of war, they were defeated and peace came back to Aether.
Source: Metroid Universe

PHAAZE / PHAZON / PHAAZE LEVIATHAN

Phaaze is a sentient planet with expansionnist behavior, mainly composed of a substance called Phazon. It sends sends huge organisms known as leviathan throughout the cosmos to reproduce by seeding other worlds with Phazon.
Phazon is a highly radioactive substance originating from the planet Phaaze, known for its extreme mutagenic and energy producing properties. Strangely, it's not only a radioactive substance, but also an extradimensional living being. The substance has been responsible for the near-destruction of two worlds, Tallon IV of the Chozo and Aether of the Luminoth. In both cases Phazon arrived on the planets via interstellar objects, now known to be Leviathans. On Tallon IV the Phazon devastated and poisoned the ecosystem, eventually destroying the Chozo society that existed there. In Aether, the Phazon Meteor struck the planet and split it into two dimensions, driving the planet and its inhabitants into turmoil.
Phazon is a highly radioactive, mutagetic, and semi-sentient substance. Phazon is also capable of self-reproduction, making it's ability to spread incredibly efficient. Most Phazon is blue in color, except for the much more potent orange variation, whose radiation and mutagetic levels far exceed the normal blue Phazon. Orange Phazon also has small bluish hued energy spheres that appear on the surface, which act as spawning nests for Fission Metroids. Red crystals with low amounts of Phazon energy are found in the Magmoor Caverns. Because of this, the Pirates intended to put them on the market when Phazon operations are complete. There are also Black Phazon Crystals only found on Phaaze. They are commonly mined by Space Pirates. This suggests that there are unknown types of Phazon elsewhere.
Phazon exists in many phases. It is most commonly seen as Phazon ore, appearing as a network of blue veins and crystal-like sacs. A more concentrated form of Phazon is known as liquid Phazon, liquid Phazon takes on the traits of a dense gel. Large amounts of Phazon are usually seen with bolts of Phazon energy, appearing as arcs of static electricity. This is probably due to the high amount of unstable energy Phazon is constantly producing.
Phazon also demonstrates a trace amount of sentience. Left-over Phazon energy after a Leviathan impact can manifest itself into Phaazoid, mindless Phazon energy that is constantly discharging itself.
Phazon releases unique energy in the form of Phazon radiation. Exposure to any amount of Phazon radiation can be deadly. Most bioforms in direct contact with Phazon ore/liquid die within seconds. Even living within an area with high Phazon concentration can be fatal over time. However, bioforms with prolonged Phazon exposure that do not die are mutated horribly. Exposure to Phazon radiation destroys brain cells and cognitive thought in sentient beings, yet it also sees a gain muscle mass and other beneficial abilities. Phazon exposure, while destroying the mind, makes beings hunger for more Phazon. In turn, corrupted beings also have a natural instinct to protect Phazon and its source. Humans seem to be immune to the mental effects of Phazon.Chozo, on the contrary, are especially weak to it, for even their ghosts become insane from Phazon exposure.
Phazon can also be used as an energy source. Phazon, because of the intense radiation it produces and its mutagenic properties is a deadly toxic substance. Any planet with Phazon corruption left unchecked will "kill" the planet. The planet will slowly turn into pure Phazon, becoming like Phaaze. Many life forms exposed to Phazon radiation expire within seconds. However, some life forms can survive the Phazon exposure, although the price to be paid is horrible mutation of the body and mind. Subjects exposed to Phazon over long periods of time may develop a form of mental breakdown known as Phazon Madness or Phazon Sickness. This condition affects the mind, driving the subject to the point of mental instability and a constant hunger for more Phazon. Life forms that survive Phazon exposure usually gain increased muscle mass and newfound abilities, but suffer a decline in cognitive thought and general lifespan.
Although a dangerously radioactive destructive substance, the Space Pirates have taken advantage of Phazon's mutagenic properties to create a powerful biologically engineered army of Phazon-enhanced Pirates and other creatures. The Pirates had begun a series of Phazon exposure experiments with native Tallon IV life forms to test Phazon mutagenic abilities, even managing to infuse sapience in inorganic matter. In further experiments, the Pirates had begun Phazon infusion experiments, injecting subjects with pure Phazon.
Phazon primarily appears as a radiant semisolid or soliquid. The most abundant type of Phazon found within the game takes on a more solid form, appearing as a network of veins or large crystal-like sacs. Less freqeuntly, a purified concentrated form of Phazon can be found having gel-like traits. The first installment of the series initially revealed two variations of Phazon, a regular blue type and a much rarer, but exponentially more potent orange variation.
Leviathans' sole purpose is to spread phazon from the planet Phaaze to corrupt planets across the Universe in order to create more Phazon-based planets, similar to Phaaze. The core of the Leviathan is very strong and can only be destroyed by a stream of Phazon or a powerful laser blast. These creatures were notable not only for their ability to create Phazon, but mostly because of their most powerful ability: generating wormholes which allow them to travel anywhere throughout space.
Leviathans are the "children" of Phaaze. Born in a serpentine organ deep within the planet, they feed on vast amounts of Phazon energy until they develop a Phazon core, which marks their transition into adolescence.
Before this, they are extremely unstable, though naturally extremely resistant, and cause massive explosions if damaged before full maturity. Once they reach adolescence, the Leviathans are slowly pushed upward to the surface until they mature to their adult size. The oldest Leviathans are up closest to the surface while the youngest are below. As Leviathans are launched into space, the younger ones move closer and closer to the surface. Once Phaaze has found a planet to corrupt, it launches the Leviathan into space, in hopes of impacting a planet.
Leviathans are a silicon/phazon-based bioform in that, at full maturity, they appear to be made of a rocky (perhaps a form of Phazite) substance which is likely why information pertaining to them refers to them as meteors. They are covered with large patches of Phazon and have long tentacles growing out of their sides. The inside of a Leviathan appears similar to a cave containing various Phazon based life and Phazon generating organs. The passages that lead to the core chamber of the leviathan appear as transparent tubes. There are doors in the Leviathan that seem to be a type of sphincter valve with a weak energy field covering it. The core chamber itself is a large spherical room. This room has many pulsating/moving objects which may be organs. The core itself resides at the top of the chamber in a sealed sac-like room. The core appears to be a large ball connected to the ceiling by a cord that it moves around with. It is covered in Phazon ornaments and has an insectoid appearance with several eyes and a mandible-like mouth. The chamber is also usually where the Leviathan's guardian resides. The Leviathan on Tallon IV appears to have been consumed by Metroid Prime due to the creature's omnipresent lust for Phazon, but this has not been proven.
After ejecting from Phaaze, the Leviathan will create a wormhole to shorten its journey to the intended planet. The Leviathan will home onto its closest target and impact the planet, spreading phazon from the collision. Eventually, the Phazon core of the meteor slowly seeps its way into the planet, spreading Phazon and replacing the ecosystem with one that is Phazon-based. The Leviathan attracts a native creature and corrupts it with massive amounts of Phazon. The corrupted creature serves as the Leviathan's guardian, to protect its Phazon core. Sometime after this, the Leviathan itself will die, leaving behind the "husk" of it's body.
SOurce: Metroid Universe. Text adapted form the aliens.wikia.com and the Wikitroid.

SPACE PIRATES / ZEBESIANS

Planet of Origin: Ultragia, The Pirate Homeworld is plagued by a steady stream of Acid Rain, harming any creature without proper protection. At some point, the planet was also hit by a Phaaze Leviathan which corrputed it.
The Space Pirates are an aggressive expansionnist sentient scavenging species that has developed or gained space faring capacities. They have been known to experiment with Metroids and Phazon, leaving dangerous results.
Roughly humanoid, Space Pirate physiology includes a wide range of morphological variation – their base forms have hands featuring two thumbs and a single finger, but many are genetically engineered with lobsterlike claws. Some of these clawed pirates have their other arm replaced by a massive blade rather than a second claw. The Space Pirates have repeatedly used Phazon to mutate their own species.
A very militaristic race, in their society, obedience is a strict law and the death penality quite common. They are extremely stringent about possessions— thievery within their race is punished severely.
Most of their techology has either been found or stolen and focussed toward making new weapons; the same apparently goes for their culture. The Space pirates have based much of their military on the element Phazon. They set up full bases when trace elements are found. It is a highly radioactive mutagen which can increase the threat level of space pirates exponentially. Through these experiments the space pirates have created many abominations of nature. The high death toll of miners and test subjects does not deter the space pirates from this powerful resource. some Space Pirates protested against Phazon being used on their homeworld.
Note: Accroding to series director Yoshio Sakamoto, the Pirates took "Zebesian" as a general name for themselves after the conquering of Zebes, comparing it to most Americans actually being from Europe after conquering the true Native American tribes.
Source: Metroid Universe

X PARASITE

The X Parasite is an alien creature found on planet SR388. An ectoparasitoid, it kills its host and absorbs its DNA and intelligence. This ability allows it to organically absorb and implement data, such as creating a heat resistant material to wrap itself in. It reproduces through a process similar to viruses, which makes it almost invincibly adaptable. When an X doesn’t come into contact with a susceptible host it stops growing and reproducing. It can stay dormant for eternities until disturbed.
Several organisms can laso gather to form a composite creature called a Core-X. Individuals can be forced out from a Core-X gathering.
They have one predator, the Metroid, genetically engineered lifeforms created by the Chozo to destroy them.
Source: Metroid Universe

CHOZO

The Chozo are a bipedal avian species which developed an highly advanced interstellar civilisation. The species used to have a pair of wings that enabled flight on their backs which became vestigial at some point. Due to their great longevity, old age wreaked havoc on their ability to reproduce, causing a steep decline in their numbers. They are now thought to be extinct, possibly transcendent.
Some 1500 years ago, the Chozo culture was peaceful, prizing knowledge in all its forms. They were explorers, seeking scientific and technological advancement, interstellar exploration, and primal shamanistic wisdom. Balance between technology and spiritualism was a defining trait of their culture and they often shared their wisdom and knowledge with other species, such as the Luminoth, the Reptilicus and the Ylla. Many of their structures were built of stone, although they were capable of using far more advanced materials and building techniques.
The Chozo are responsible for creating the original Metroids or "Ultimate Warrior" on planet SR-388. It is believed that the Metroids were created in an attempt to stop the X Parasites from destroying SR-388's ecosystem. Chozo ruins have been discovered on the planets Zebes, Tallon IV, SR-388, Elysia, and Bryyo.
SOurce: Metroid universe.