Metroid (species)
Metroid is a fictional species of alien predators in the video game series of the same name, originating from the planet SR-388. They share aspects of their behavior with both predators and parasites. Metroids feed on the "life energy" of their prey in a manner similar to leeches draining a host organism's blood. However, Metroids normally drain enough energy to kill their victims. The name 'Metroid' means 'ultimate warrior' in the Chozo language.
Physiology and Morphology
The body of infant Metroids consists of a gelatinous substance, similar to what a jellyfish is made of, encasing a set of four red nuclei which resemble raspberries. They have two pairs of mandibles used for extracting life energy from their prey. Once they have a grip on their prey they hang on until finished feeding. They have an endless appetite and will feed again and again, without stopping, if food is abundant. In early stages of their development, Metroids hover in the air. Metroid Prime 2 explains that they defeat gravity by using kinetic energy they store in their body. These larval Metroids are the ones most often encountered in the Metroid games.
In their natural life cycle (as seen in Metroid II and the end of Metroid Fusion), Metroids gradually metamorphose to take a somewhat reptilian form, growing a hard organic shell, a head, and limbs around their amoeba-like center. Their shell is impervious to all weapons Samus can wield. However, part of their gelatenous center remains exposed in all forms except the Metroid Queen, and this exposed area is vulnerable to explosive missiles and, under some circumstances, freezing. As they grow, Metroids also gain the ability to project energy, such as by creating lightning or blowing fire.
When mutated by Phazon (as seen in the Metroid Prime series), Metroids retain their jellyfish-like appearance, but grow longer tentacles or take on elemental attributes.
The Metroids live on a mysterious energy that they drain from their victims. No one has been able to figure out just what it is — no blood or other body fluids are lost during a Metroid attack, but the Metroids grow larger on it and the victim dies without it. As of Metroid Prime 2: Echoes, this energy is referred to as life energy. The Space Pirates are quite interested in this ability.
Besides draining life energy from victims, Metroids also have the ability to transfer stored up life energy into another lifeform, healing them. Federation scientists were greatly interested in this aspect of the Metroids, as it promised to be a significant breakthrough in medical science. This avenue of research was lost when the only Metroid ever to be successfully domesticated was destroyed by the Space Pirate's Mother Brain.
One of the species' major weakness is an extreme sensitivity to cold temperatures – they can be pacified at 20°C (68°F). Once frozen, Metroids can be shattered with explosive missiles. They are generally very resistant to most other forms of weaponry. Exposure to beta radiation causes them to divide.
History:
They were said to have been originally discovered by the Galactic Federation while researching SR-388. Not long after that, the Space Pirates boarded a ship in which some Metroids were being transported and stole the specimens, taking them to their base deep within the planet Zebes. Shortly after that incident, female bounty hunter Samus Aran was sent to Zebes to destroy the Space Pirates and their stolen Metroids.
The Space Pirates have conducted a number of experiments on the Metroids. In the first Metroid game (Which was re-released as an enhanced remake called Metroid: Zero Mission) the Space Pirates planned to harness the power of the Metroids as a bioweapon to make their forces invincible. Samus Aran later infiltrated and destroyed the base.
The Metroids themselves do not show up until the final level of the game, the Tourian area. There, they are the only enemy aside from the base's automated turrets. Metroids are significantly larger than the other regular enemy types the player has previously faced, and can only be killed by a specific combination of weapons (the ice beam plus missiles).
In Metroid Prime, a few surviving Space Pirates found the mutagen Phazon on the planet Tallon IV and used it to rebuild their army. They exposed the Metroids to it, along with many other life-forms, including themselves. In the same game, new Metroid developmental stages were revealed: infant Metroids, the 'Hunter' Metroids which had orange pigmentation and two energy-extracting tentacles; and 'Fission' Metroids, which reproduce into two different Metroids, each weak to a different beam according to their colouring. However, these stages were likely brought about by Phazon mutation, as they contradict the natural life cycle seen in Metroid II. Also seen in the game is a creature called Metroid Prime that may be a Phazon-evolved Metroid, but this fact is never made clear. The Space Pirate logs in the North American version of the game say that it has genetic relations to the Metroids, but this was removed in the PAL release of the game. Metroid Prime is capable of producing Fission, Hunter, and infant Metroids.
Metroid Prime 2: Echoes had the Space Pirates bring along Metroids (referred to as Tallon Metroids and having red instead of green coloring) on their trip to Aether. The Ing would later possess some Metroids, creating Dark Metroids. Also seen are Metroid cocoons, which release very small infant Metroids who need to come in contact with Phazon in order to grow to the size of the Tallon Metroids. Very young infant Metroids cannot yet absorb energy, and use ramming attacks to damage their foes instead. The game's villain Dark Samus seems to be some form of Metroid Prime, but much of its history is still unknown.
After 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. It was in this game that the whole natural life-cycle was revealed.
The game begins with a total global Metroid population of 39 (such a relatively small number does make some degree of sense, as a stable ecosystem can only naturally sustain a limited number of top predators). Samus' goal is to explore SR-388 and hunt the Metroids down one by one. As she progresses further into the planet, the Metroids continue to evolve further into their life-cycle, culminating in the Omega Metroids. Samus eventually makes her way into the Metroid nest at the center of the planet, destroying several larval Metroids before engaging in a final battle with the Metroid Queen.
After destroying the Queen, Samus did end up destroying all Metroids... almost. An infant Metroid hatched and imprinted on her as its mother. This infant helped Samus escape from SR-388 as it began to collapse, so she took it back to the Federation Academy.
Super Metroid took place directly after Metroid II, continuing the storyline. The infant Metroid that had imprinted on Samus was studied, and it was found that the Metroids' potential as life saving creatures was as great as their destructive powers. Right after Samus left the Academy, the Space Pirates besieged it and Ridley stole the infant, taking it back to the Space Pirates' rebuilt base on Zebes. Samus chased them to return the last Metroid to the Federation.
Unfortunately, the baby Metroid turns out to no longer be the last Metroid, as the Space Pirates quickly use it to clone a new army of feral larval Metroids. Once again, these Metroids appear near the end of the game as particularly difficult enemies.
The baby Metroid is also discovered late in the game, only much bigger and stronger (several times the size of even a regular Metroid). It overpowers and begins to feed on Samus, but eventually recognizes her as its "mother", and flies away. It appears once again to intervene in the final battle between Samus and Mother Brain, attacking Mother Brain's monster form just as she is about to finish off Samus. The baby Metroid drains Mother Brain's life energy and uses it to heal Samus, but Mother Brain revives and begins blasting the baby Metroid as it attempts to restore Samus' life. The baby Metroid manages to heal Samus completely and give her the power needed to destroy Mother Brain, but at the cost of its own life. Thus perishes the last Metroid... at least for a while.
On a side note, this game is actually the first to state that Metroids were made by the Chozo. However, since Fusion was the first game to directly state this, it often gets the credit for this revalation. Some fans dislike this part of the story.
Metroid Fusion takes place several years after Super Metroid. On planet SR-388, all was not well - the Metroids had been the top predators, and with them gone the ecosystem was thrown completely out of balance. Samus was hired to protect some Federation scientists who were studying the recovery of the SR-388 ecosystem. While they were on the planet, Samus was infected with a then-unknown parasite that was later named the X Parasite. She was rushed back to Federation Headquarters with a minimal chance of survival, and was saved when a sample from the last Metroid was injected into her.
The Metroids had evidently had a taste for the X and an immunity to them. This makes sense, as it had recently been discovered that the Chozo, the same people who had built Samus' Power Suit, had created the Metroids to stave off the pending ecological disaster on SR-388. The X were too efficient for the good of the ecosystem, and so the Metroids were introduced to keep them in check. The X were now loose on the Biologic Space Labs station in orbit over SR-388; with the now partially Metroid Samus the only person able to fight them, she was sent to eradicate the X infestation.
Later in Metroid Fusion, it was revealed that the Federation had a secret Metroid breeding program going, presumably based off of clones of the last Metroid. Not only has the Federation managed to successfully clone the larval Metroids, but they have also induced them to mature through their life-cycle as well. The program was destroyed by a powerful X Parasite mimic of Samus, the SA-X. However some of the Metroids escaped, overpowered the SA-X, and began devouring X parasites throughout the station. This actually worked to Samus' favor, as the Metroids cleared the station of enemies, while Samus never actually encountered any face to face in combat.
However, at the very end of the game, Samus' path to her escape pod is blocked by an Omega Metroid, which began attacking her. The Omega Metroid proved impervious to all of Samus' weapons, and she had not been able to obtain an Ice Beam due to the Federation's belief that she could no longer use that weapon due to her own Metroid DNA. However, the SA-X appears and began to attack the Omega Metroid with an Ice Beam, wounding it but ultimately being destroyed by it. Samus merged with the defeated SA-X, regained her Ice Beam, and used it to destroy the Omega Metroid and escape the station.
Any Metroid survivors remaining onboard the station were killed when said station was destroyed by its self-destruct sequence. Samus Aran is now, therefore, the last remaining being known to have Metroid genetics.
Cameos
A creature bearing a startling resemblance to the Metroid appears in Kid Icarus, and is called Komatayo. The resemblance is most likely intentional, as Nintendo developed and released Kid Icarus and the original Metroid at approximately the same time. Another resemblance can be seen in the water areas in the NES game, Blaster Master. This resemblance may be to use a jellyfish design for one of the underwater enemies, thus a seeming relationship to Metroid larva.
Also, in Kirby's Dream Land 3 there is a level with several Metroids in it. If a player kills them all, Samus takes off her helmet at the end of the level, otherwise she simply stands by the goal.
A Metroid trophy is available in Super Smash Bros. Melee.