Metroid (species)

Metroids are a species of predators in the video game series of the same name, originating from the planet SR-388. Metroids feed on the "life energy" of their prey in a manner similar to the way leeches drain a host organism's blood. However, Metroids normally drain enough energy to kill their victims. According to the Metroid Fusion instruction manual, the Metroids were created by the Chozo to stem the spread of the X parasites. While the name "Metroid" was given to the creatures by the Federation science team that made the discovery, it turns out that the Chozo word for Metroid (which is, as of yet, unknown) translates to "Ultimate Warrior."

Physiology and morphology
The body of a Metroid consists of a thick gelatinous membrane, resembling a jellyfish, which contains a set of three red, raspberry-like nuclei. They have two pairs of mandibles, one for gripping their prey and the other for extracting its life energy. In early stages of their development, Metroids hover in the air. Metroid Prime 2: Echoes explains that they defy gravity by using kinetic energy that they store in their body. These larval Metroids are the ones most often encountered in the Metroid games.

Metroids are vicious predators with no natural enemies. Once attached to their prey, they are very difficult to dislodge and will otherwise drain their victim completely, killing it. They are known to finish their victims in a matter of seconds. 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 by concussive weaponry (such as missiles), killing the Metroid.



In their natural life cycle (as seen in Metroid II: Return of Samus and the end of Metroid Fusion), Metroids gradually metamorphose to take a somewhat reptilian form, growing a hard organic shell, a head, and limbs. The shell removes their weakness to cold temperatures, but most forms retain a section of weak, uncovered membrane, making them vulnerable to attack. The only known forms with complete shells are the Metroid Queen and Metroid Prime. The egg-laying Metroid Queen appears to be the only form in which Metroids can normally reproduce. As they grow, Metroids also gain the ability to project bolts of static electricity and spit their toxic saliva as attacks.

When mutated by Phazon, metroids gain various odd qualities. (See Phazon for notes on Phazon-mutated Metroids.) Exposure to beta radiation causes them to asexually reproduce by dividing, much like a cell undergoing mitosis.

The Metroids live on a mysterious energy that they drain from their victims. What this energy is is unknown, as the victim loses no bodily fluid but perishes nonetheless. As of Metroid Prime, this energy is referred to as life energy. Metroids are stated to be energy-based organisms and increase in mass as they drain energy. Metroids can also feed off the energy used by Samus's Power Suit, which will protect Samus herself as long as it is active.

Besides draining life energy from victims, Metroids also have the ability to transfer stored life energy into another lifeform, healing it, as shown in Super Metroid.

Metroid
In Metroid, Metroids 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, bounty hunter Samus Aran was sent to Zebes to destroy the Space Pirates and their stolen Metroids.

Metroid Prime
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. This revealed two new stages in Metroid development: 'Hunter' Metroids which had orange pigmentation and two energy-extracting tentacles and 'Fission' Metroids, which split into two smaller Metroids when attacked. These stages are presumed to be the result of Phazon mutation, as they contradict the natural life cycle seen in Metroid II, and are called Tallon Metroids in Metroid Prime 2: Echoes. Also seen in the game is a creature called Metroid Prime, which is suggested to be a Phazon mutated creature with an unknown relation to Metroids.

Metroid Prime: Hunters
Metroid Prime Hunters is the only game in the Metroid series that does not feature Metroids. It does, however, feature Quadtroids, a genetically engineered species that is similar in appearance and function to Metroids.

Metroid Prime 2: Echoes
InMetroid Prime 2: Echoes, the Space Pirates bring Metroids with them to Aether. Metroids in this game appeared with both red and the traditional green membranes. The Ing later possessed some Metroids, creating Dark Metroids. Also seen are Metroid cocoons, which release very small infant Metroids which need to come in contact with Phazon in order to grow to the size of normal Metroids. Very young infant Metroids cannot yet absorb energy, and instead use ramming attacks to damage their foes. The logbook scan for these infant Metroids suggests that the Space Pirates may have somehow created this kind of Metroids to be less dangerous and easier to transport, this is supported by the fact that in the end of Metroid 2: Return of Samus, the Metroid hatchling already is in its most usually seen (larva) form when it hatches, as Samus approaches it.

Metroid II: Return of Samus
In Metroid II: Return of Samus, 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 several encounters with the creatures. It was in this game that the natural Metroid life-cycle was revealed.

The game begins with a total global Metroid population of 39. Samus's goal was 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, a result of stronger Gamma Radiation, culminating into the Omega Metroids. Samus eventually makes her way into the Metroid nest at the center of the planet, destroying several Metroids before engaging in a final battle with the Metroid Queen.

After the Queen was destroyed, an infant Metroid hatched and imprinted Samus as its mother. Because of Samus's efforts, this infant was the last surviving Metroid in the galaxy. It helped Samus escape from SR-388, and she took it back to the Federation Academy.

Super Metroid


In Super Metroid the Metroid larva 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 Ceres Station, the Space Pirates besieged it and Ridley stole the Metroid larva, taking it back to the Space Pirates' rebuilt base on Zebes.

The Space Pirates quickly used beta rays to multiply the Metroid into a new army of feral larval Metroids. In Maridia Samus also finds many Space Pirate attempts of clones of the Metroids called Mochtroids. While they could leech life, they were weak and could not latch onto their prey. At the end of the game, the Metroid larva sacrificed itself to save Samus, causing the Metroid species to become apparently extinct.

Metroid Fusion
Metroid Fusion takes place some time after Super Metroid and is considered "Metroid IV" in the official timeline. On planet SR-388, 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 an X Parasite. She was rushed back to Federation Headquarters with a minimal chance of survival. It had recently been discovered that the Chozo had created the Metroids to prey upon the X Parasites, which were dominating the ecosystem of SR-388. Using this information, the Federation saved Samus by injecting her with a vaccine made of a DNA sample from the last Metroid.

Later in Metroid Fusion, it was revealed that the Federation had a secret Metroid breeding program going, presumably based on clones of the last Metroid. The program was destroyed by a powerful X Parasite mimic of Samus, the SA-X. The entire section was detached from the station and ejected into space, just after Samus escaped, completely destroying the Federation's research. However, one Metroid had escaped and advanced to Omega level, and Samus had to defeat it before evacuating.