Metroid

The Metroid is an ectoparasitoidic life form created by the Chozo to combat the X Parasite on SR388. However, due to their ability to collect life energy and feed off of it, Metroids have been harvested for experiments and use as weapons by the Space Pirates.

Origins
On SR388, the X Parasite threatened to destroy the ecosystem, due to the high rate of reproduction. However, the Chozo stepped in to save the planet, and created Metroids. "Metroid" is the Chozo word for "ultimate warrior." The Metroids kept the X Parasite numbers in check, and became the dominant predators of SR388. (Metroid Fusion)

Cultivation and Extinction
The Metroids were first found on SR388 by a Galactic Federation scout ship. However, while en route with a metroid, the scout ship was hijacked by the Space Pirates.

The Space Pirates saw Metroids as a weapon they could use, due to their parasitoidic properties. The Space Pirates captured and cloned many Metroids, with some damage to their own numbers. With the Metroids, the Space Pirates engaged in experimentation, using phazon for mutations.

Other forms of Metroids mutated due to the phazon, such as the Hunter Metroid and the Fission Metroid. Metroids were brought to Zebes, Tallon IV, and Aether, where they were experimented on and cloned. While on Tallon IV, a life form called the Metroid Prime was found. It was highly dependant on phazon to live, and due to its ability to take in energy and use it to feed, the Space Pirates called it a Metroid, although whether the Metroid Prime is an actual Metroid is unknown. (Metroid Prime).

Seeing the dangers the Metroids posed to the galaxy, the Galactic Federation attempted to destroy them. After two failed attempts by the Federation's army to eradicate the Metroids on their home planet of SR-388, they called on Samus Aran to deal with them, as she had previously been the only person able to survive an encounter with the creatures. Samus destroyed all the Metroids on the planet, including the Queen, save one; a larva metroid that believed Samus was its mother. Samus brought back this larva metroid to Ceres Space Station to be used for research. (Metroid II: Return of Samus)

This didn't last long however. Soon Ridley of the Space Pirates captured the larva Metroid and brought it back to Zebes to be cloned. There, the Space Pirates first unsuccessfully cloned the Metroid, creating Mochtroids. They did manage to clone the Metroids successfully, only to be destroyed by Samus. During Samus's battle with Mother Brain, the Metroid that believed Samus to be her mother gave Samus back life energy during a critical moment, leaving Samus to destroy the Mother Brain. However, the Metroid did not survive the encounter, leaving the Metroids to be presumably wiped out from the Galaxy. It should be noted that the Metroid which saved Samus Aran was massive, giving proof that Metroids come in varied sizes. (Super Metroid)

After effects
Once all the metroids were gone from SR388, the X Parasite could reproduce again, and became a threat to the ecosystem. Samus Aran attempted to fight the parasite, but was unsuccessful. The parasite went inside Samus's body, leaving Samus's body integrated with her suit. Parts of it were surgically removed, but she was dying. there was a solution: a Metroid vaccine. The Metroid vaccine killed the X parasite, and saved Samus's life- again.

The Metroid that Samus brought back from SR388 was cloned on the BSL Research Station orbiting SR388. The Federation mangaged to clone each form of Metroid, up to the Omega Metroid. Whether they managed to clone a Queen, or why, is unknown. The Metroid cloning center was jettisoned into space and self-destructed after a SA-X breached it. (Metroid Fusion)

Biology and Life Cycle
The Metroid has a several-stage lifestyle.

Egg-larva
Metroids start out as Eggs, presumably laid by the Queen. They then hatch into small Metroid larvae. The larva is small, and floats in the air.

Metroid
The Metroid has a thick gelatinous membrane, resembling a solid jellyfish, which contains a set of red, raspberry-like nuclei. They have two pairs of mandibles, one for gripping their prey while the other extracts its life energy. Metroids hover in the air, defying gravity by using kinetic energy they store in their body.

Once attached to their prey, they are very difficult to dislodge and will otherwise drain their victim of their life energy completely, killing it. They have an endless appetite and will feed on any and all living creatures they come across, with the single exception of their own species. This immense threat is compounded by their invulnerability to most forms of weaponry. They have only one real weakness: an extreme sensitivity to cold temperatures. Once their membrane is frozen it can be shattered with explosives, such as a small explosive projectile.

When a Metroid takes in energy, it grows in size. Eventually, it will metamorphose to its next form.

Alpha Metroid
The Alpha Metroid is the next stage in the Metroid life cycle. While Alpha Metroids can hover like their previous form, they have four limbs, strange tusks, a horn, and two pairs of eyes.

Gamma Metroid
The Gamma Metroids are a grown version of the Alpha Metroid. The limbs are now longer and more muscular, the carapace is thicker and bigger, and the horns are stronger and thicker. Another pair of eyes is added to the head of the Metroid.

Zeta Metroid
Zeta Metroids are more of a dinosaur-like analog. This form of the Metroid has only a small bit of the blue membrane left from the unmorphed Metroid left over. The Zeta has two muscular legs, two short arms with claws at the ends, and a tail. Having lost the ability to hover, they use their legs to to leap with great speed as well as strength.

Omega Metroid
Besides the Queen Metroid, this is the fullest a Metroid can evolve. The blue membrane, usually on the underbelly on the Metroids, is now concealed. The legs, arms, and tail are now fully developed. Another pair of eyes is added, making a total of four pairs of eyes, Omega metroid's large leg muscles make it a quick runner and a mighty jumper.

Queen Metroid
The Queen Metroid is so far the only form of Metroid known to be able to reproduce normally. The queen is much bigger than any other form of Metroid, and stands on all fours as opposed to walking on two, like the Zeta and Omega Metroids. The neck of the Queen can extend to high lengths, to better protect her young.

Tallon IV Metroid
The metroid from tallon IV, due to phazon exposure,a metroid evolves into a hunter metroid, instead of an Alpha Metroid, a form never seen before. Through dedicated research it has been discovered that the process of feeding phazon to metroids is not at all enjoyable to them, much like how a goose does not enjoy being force fed in preperation for foi gras. Our scientists have stated that the metroid's reaction to phazon is "Much like a humans reaction to a cocaine milkshake.". The Tallon metroid exposed into orange phazon, evolves into a Fission Metroid.(Metroid Prime)

Fission Metroid
This Tallon Metroid variant was exposed to orange phazon and has the hability to reproduce using mitosis. This Metroid variant has been seen only on the impact crater on Tallon IV.(Metroid Prime)

Metroid Prime


Metroid Prime´s origin is unknown. It could have evolved from a Metroid Larva exposed to Phazon, this, based on the Space Pirate Log wich mentioned that Metroid Prime was at first at a small form, and now it is growing bigger. At first, Metroid Prime is in its exoskeletal form. When fighting with Samus Aran, is exoskeleton was heavily damaged, and then its essence form appeared. While in its essence form, Metroid Prime is able to create Tallon Metroids and its variants, make wave attacks, and become invisible to the naked eye. Metroid Prime in esscence form is invulnerable to all weaponry, only a phazon based attack can damage him. Samus used phazon pools created by the Metroid Prime, activated her Phazon Beam and killed it. Metroid Prime in its last breath, stole Samus' Phazon Suit and formed into Samus' new enemy: Dark Samus. There are rumors that Metroid Prime is part X-parasite, which are false. The reason is because, when Samus beat Metroid Prime and it reverted to an orbish form, people thought it looked like a Core-X. Please note that Dark Samus and SA-X are two completely different characters. SA-X seems to have Samus' face. SA-X only uses techniques it copied over from Samus. Dark Samus has her own style.

Dark Samus
Using the phazon suit that it stole from Samus, Metroid Prime evolved into Dark Samus, a phazon based clone of the original Samus containing her genetic material. Samus' first encounter with her evil twin was on planet Aether, which was recently damaged by a phazon meteorite. The meteorite created a Dark version of Aether. Somehow, in Dark Aether, a lifeform known as The Ing was born, devastating Aether.(Metroid Prime 2)

Darkling Metroid
The Ing have parasitic properties, and infect potential fighting creatures, using them as a vessel for combat. When the host is killed, the Ing escapes and finds a new host. The Metroid are enemies of the Ing and attack them on sight. However, some ings have managed to infect metroids, making them even more powerful.(Metroid Prime 2)

Extrapolated Life Cycle Due to Phazon Exposure
Due to experimentation by the Space Pirates on Tallon IV, as well as numerous logs, it can be safely determined that the life cycle of a Metroid is altered by atmospheric conditions. The presence of phazon will cause a Metroid to undergo many different kinds of mutations, many of them varied.

Stage 1: Phazon/Tallon Metroid
It is said that the Phazon Metroid is related to the Tallon Metroid, due to its reliance on phazon. It is likely that this particular strain is either native to the planet Phaaze or was placed there by Space Pirates. Similarly, the related Tallon Metroid may have been native to the planet Tallon IV long before Space Pirates arrived with Metroids. Either possibility yields a similar end.The Phazon Metroid is characterized by its complete dependence on phazon.

Stage 2A: Metroid Hatcher
The Metroid Hatcher is an enormous Metroid mutated through phazon exposure. The Metroid Hatcher has a large maw and long tentacles. It "births" live Metroids through its maw. This variant serves to increase the Metroid population quickly without the need for beta-ray fission or egg gestation time. It is unknown whether this variant also lays eggs. It is also unknown what conditions cause the phazon mutation to lead to this form rather than the "Hopping Metroid" (see next).

Stage 2B: Hopping Metroid
In this variant of Metroid mutated by phazon exposure, the creature has lost its ability to fly and has gained the use of powerful legs. It is believed that either this form or the "Phazon Metroid" lays eggs, due to their presence being unexplained by the "Hatcher Metroid", which "births" live young. It is believed that this form can only be found where metroids are exposed to massive quantities of phazon, such as Phaaze, or proximity to a Leviathan/Seed.

Stage 3: Metroid Prime
Metroid Prime is currently thought of as the height of Phazon Metroid mutation. It is a direct mutation of the "Hopping Metroid" due to obvious similarities and evidence. There have been two documented instances of this creature.

One instance is on Tallon IV, where this creature was found lurking in the Impact Crater. We know that the planet was impacted by an interstellar object originating from the planet Phaaze. This object was presumably a natural Leviathan (natural having the meaning of lacking the Space Pirate technology gained in later years by the entity Dark Samus; technology which augments the Leviathan into a rapidly acting phazon seed). When this Leviathan was near death, sometime after impact, it followed its natural instinct by choosing a creature in close proximity and corrupting it with immense quantities of phazon to cause it to act as a guardian until the planet has been transformed. It is debatable how the dying Leviathan came into contact with a Metroid, but it would appear that it mutated first into a "Hopping Metroid", and then through continued massive exposure, into the creature known as Metroid Prime.

The second instance is found on the planet Phaaze, where dead husks can be found which are said to be identical to the creature fought in the crater on Tallon IV. This instance is simple to explain. The planet Phaaze is, in essence, entirely phazon-based. The level of phazon radiation there is enormous. Whether the Metroids found there are native to the planet or were brought by Space Pirates is irrelevant. Their presence confirms that the massive levels of phazon would eventually mutate each Metroid into a "Hopping Metroid", and then into a "Metroid Prime". All three forms are present on the planet Phaaze, including vast amounts of "Hopping Metroids" therefore presumably there were other "Metroid Prime" bioforms on the planet, perhaps elsewhere.