Metroid(species)

The base larva form of a metroid

Originating from the planet SR388c, the metroid first became known to the universe at large when the Space Pirates stole a specimen from a Galactic Federation research vessel and attempted to exploit them as bioweapons. Since then, the species has been spread out on numerous planets, endangering all life present due to the metroids living off of the mysterious "life energy" of their prey.

The metroids were thought to be created by an ancient precursor category civilization, though their motive for doing so remained a mystery to the rest of the universe. Eventually, it came to light that the Chozo, specifically those of the The'nau tribe, were responsible for genetically engineering the species in order to prevent the spread of the more dangerous Erris hyperparasite lifeform. Appropriately, the word "metroid" in the ancient Chozo language roughly translates to "hunter without equal", or "perfect predator".

## Biology and characteristics

The metroids on SR388 possess a multitude of different body structures and sizes, a result of their complex life cycle that drastically alters their physiology as they grow. They begin life as jellyfish-like creatures before molting into a form akin to an arthropod's, until eventually reaching adulthood with the features of a theropod; various Metroid husks are discarded throughout the entire process.

Despite their various forms, there is a specific physical feature shared by all metroids inhabiting SR388: the presence of a translucent, protective membrane enclosing a red nucleus. The nucleus has numerous neuron-like connections extending from it which connect to the inner surface of the membrane. Its function is unknown, but it is of vital importance to the metroid, as destroying this structure kills the organism. An even greater mystery of their biology is their capacity to perpetually float in midair, as seen in younger individuals, despite lacking any visible means of propulsion.

Metroids are highly aggressive creatures with no known natural predators and, are thus at the top of the food chain on SR388c. They feed on bioenergy from their prey in a manner akin to the way a lamprey or a leech drains a host organism's blood. It is unknown exactly how the Metroids extract this life energy or what, in fact, the latter consists of - the metroid's victim simply dies and is impossible to resuscitate. Metroids can also feed on other forms of energy, such as those found within stellar vessels, technological equipment and radioactive substances.

The corpses of those killed by a metroid are usually left with a dull, grey coloring that indicates their loss of life energy, and remain "stuck" in whatever pose they took during the final moments of their lives, usually one that expresses struggle, agony, and fear. An example is a body standing on its legs while its hands are clamped to its chest, a statue-like stance that is normally impossible for a corpse to take if killed by other means. These remains are also in a state of such extreme fragility that a mere touch will cause them to crumble into an ash-like substance.

Metroids on SR388c produce a strange substance akin to webs through unverified means. It is initially gelatinous, but in time forms into durable structures that serve as homes for the species.

### Life cycle on SR388

The first encounter between the Galactic Federation and the metroid species consisted of a etroid larva attacking the crew of a research vessel visiting planet SR388c. This incident prevented adequate data from being collected on the planet's ecosystem and consequently, it was believed for some time that the metroid larva was the only form of the entire species.

Supporting this belief was the fact that metroids cannot metamorphose into their advanced stages seen in unless they are exposed to some unknown factors native to SR388c's atmosphere, environmental stimuli, and possibly Aeion energy. As such, the growth cycle seen on SR388c has never been witnessed anywhere else.

#### Metroid Egg

An egg laid by the queen metroid. An infant metroid eventually hatches from it.

#### Infant Metroid

The infant has a simple body shape similar to a jellyfish. Perpetually floating in the air, the organism appears and behaves relatively docile, though it is known to be highly unpredictable at times and can attack without warning.

#### Metroid larva

A larva's physiology is mostly identical to an Infant's, however, its size has grown exponentially. This stage is the initial form given to the species by their Chozo creators. Seemingly unique to this stage and the previous Infant form are their responsiveness to Beta-Rays, which cause them to split and multiply within 24 hours. The larva and Infant stages can thus be grouped together as the larval phase of a Metroid's life cycle. Notable is the larva's seeming immunity to directed energy weapons, though ballistic hard rounds have been observed to have some effect, and a particular weakness to extreme colds. Certain cryo weapons have been noted to be able to freeze a larva stage solid, allowing for a direct concussive force to literally shatter the larva and kill it instantly.

#### Alpha Metroid

After shedding its larval form as a husk, the metroid is now visually akin to an arthropod, though its insect-like legs have not reached their full length and size, thus preventing their use for ground locomotion. It can discharge electricity as an offensive and defensive measure. The alpha stage metroid has gained resistance to cold temperatures, aided by a plated exoskeleton that partially covers it and helps reduce the effects of direct cold to the membrane. However, the loss of several nuclei within its green membrane has left it more vulnerable to concussive weaponry, and the metroid is not immune to freezing effects, as the membrane can still freeze and cause the alpha stage serious complications.

#### Zeta Metroid

The metroid’s transition to zeta sees a marked change in not only its appearance, but its abilities and tactics. While it retains the thick armored plates and four limbs of its previous forms, the zeta metroid gains a distinct head and neck, a torso, and a long, muscular tail. Its limbs have differentiated into distinct arms and legs, each ending in a pair of razor-sharp claws, and the creature is now equally comfortable moving on all fours or its hind legs, though it can no longer fly as it has become too heavy, now weighing nearly half a ton. The vulnerable abdominal membrane is smaller now, making it less of a target than in previous stages, and preventing it from being frozen solid. The zeta stage is also capable of spitting highly acidic mucus and breathing globs it what behaves like blasts of plasma.