Xenomorph

Xenomorphs (Latin perfectus venator meaning "perfect hunter") are a highly aggressive endoparasitoid extraterrestrial species. They are infamous for being the deadliest species in the universe, second only to the Flood. The Xenomorph hives are a third party in the Great Virgo Intergalactic War.

Physiology
Xenomorphs are a large, bipedal, and exotic, sentient species with a silicon exoskeleton.

Appearance
Notably, Xenomorphs will alter their physical appearance during development depending on the physiology of the host in which they gestate — this incorporation of physical traits gleaned from the host is designed to ensure the adult creature is better suited to the environment in which it will find itself. This ability to alter its form based on the host's physical attributes occurs at a cellular level and has been referred to as the "DNA Reflex". Historically, most Xenomorphs encountered have typically gestated inside human hosts, and therefore adopt a basically bipedal, humanoid stance, but other variations born from a wide variety of different host organisms have been seen, and as a result feature varying physical appearances. However, regardless of any physical variation resulting from the host, Xenomorphs always possess certain distinctive, trademark characteristics.

Outwardly, they have a skeletal, seemingly biomechanical (which is really their exoskeleton) appearance and are usually colored in muted shades of black, blue or bronze. Whatever the host organism, they invariably possess distinctive, elongated, cylindrical skulls, but possess no visible facial features other than their mouth. The carapace atop the head has been seen to vary, from smooth and vaguely translucent to ridged and opaque. This difference is part of a maturation process, and younger Xenomorphs, or Drones, possess the smoother, domed carapace, while older specimens, such as Warriors, feature ridges. Notably, ridges are often visible beneath the smooth dome of Drones.

The Xenomorphs' primary weapon is their inner pharyngeal jaw, which is capable of shooting from their mouth like a piston with sufficient power to smash through bone and metal. In fact, a common tactic used by the creatures to eliminate prey is to restrain the victim with their hands, immobilizing them, before killing them with a precision jaw strike to the head, piercing through the skull and penetrating the brain; this form of attack is colloquially known as a "Headbite". On several occasions, Xenomorphs have been seen to suspend the corpses of those that they kill from ceilings.

Xenomorphs have segmented, blade-tipped tails. The sharp tip has been seen to vary from a small, scorpion-like barb to a larger, flat blade. Despite their seemingly flimsy physical construction, the creature's tail makes for an incredibly potent weapon, strong enough to impale and lift a Sangheili or Jiralhanae from the floor with seemingly little effort. The tails have been used variously as stabbing, slashing and blunt force trauma weapons. Above the tails, the creature possesses several Dorsal Tubes on its back, typically consisting of two pairs — a larger upper pair and a smaller lower pair — often with a fifth, sharper spine in the centre below the base of the head. The exact purpose of these tubes is unclear.

As a result of the DNA Reflex, Xenomorphs have appeared as both plantigrade and digitigrade organisms, usually in accordance with their host. For example, human-spawned Xenomorphs typically possess humanoid hind limbs and walk upright, while Xenomorph's spawned from quadrupedal hosts (referred to as "Runners") sport double-jointed hind legs and move predominantly on all fours.

Physical Abilities
When standing upright, Xenomorphs are vaguely bipedal in form, though they adopt a more hunched stance when walking or sprinting and are equally adept at moving on all four limbs, even in instances where the host was a bipedal lifeform, such as humans. They are quite capable of running and crawling along ceilings and walls and are expert jumpers. They possess great physical strength, having been known to break through metal vent covers and welded steel doors with little effort, and even of breaking down reinforced pressurized doors over time. Their large clawed talons are more than capable of tearing humans apart, while their primary jaws are capable of producing a bite strength estimated at 6,000 psi.

Xenomorphs do not radiate heat, and their body heat matches the ambient temperature of the environment in which they are found. Adverse extremes of temperature appear to have little, if any, affect on their physical prowess. In fact, physiologically they are incredibly hardy creatures — aside from being unaffected by temperature extremes that would quickly incapacitate or kill a human, they are capable of surviving in the hard vacuum of space for a limited period of time.

Senses
Studies by Valamorius' exploration and science group have shown that Xenomorphs possess several senses. First and foremost, the creatures have sensory structures along the sides of their extended skulls that are capable of perceiving atmospheric vibrations (sound). Given the lengthy structure of the head, which gives the creature a wide field of "hearing", this is thought to be the Xenomorph's primary means of rationalizing its environment. The creatures are also capable of detecting heat via highly sensitive thermoreactive organs located behind the skull's frontal plate — which is itself constructed of the unusual C60 carbon-lattice, known to demonstrate exceptional conductive properties. Finally, the creatures possess largely vestigial photosensitive organs flanking the frontal plate; these visual receptors are thought to aid the creatures in seeing each other (Xenomorphs produce no notable body heat, a fact that would otherwise render them blind to their thermal receptors). These remnant visual organs are also thought to grant the creature the necessary depth perception required when attacking prey.

During tests, personnel discovered that it is possible to stun Xenomorph specimens through the use of a low-intensity ultrasound pulse, rendering them completely inert and relatively safe for manipulation and study. This discovery led to the development of weapons effective at disabling Xenomorphs.

According to research, the Xenomorph has a electro-reception organ at the front of its head lined with compound cells of fullerite-encased hurlantium. The internal structure is solid neurons in two binary very dense fans. The fullerite and hurlantium pick up E-waves and the binary fans create interference patterns from electromagnetic fields. This allows the Alien to receive brainwaves and electrical signals and enables it to assess another animal's physical characteristics by seeing its subtle body. That is why strong electromagnetic fields affect the Aliens.

Life Cycle
"Full Article: Xenomorph Life Cycle" The Xenomorph life cycle is a complex process comprising several distinct stages. The creature begins its life as an Ovomorph, or Egg, laid by a Queen, which hatches a parasitoid larval form known as a Facehugger, which in turn "impregnates" a living host with an embryo known as a Chestburster. After a gestation period of several hours, the Chestburster erupts violently from the host's chest, resulting in the death of the host. The Chestburster rapidly matures to an adult phase (within a matter of hours), shedding its skin as it grows and replacing its cells with polarized silicon. Due to the DNA Reflex, horizontal gene transfer during the gestation period leads the adult Xenomorph to take on some of the basic physical attributes of the host from which it was born.

The Xenomorph life cycle bears similarities to that of certain parasitoid insect species found on Earth. Its use of a living host as an incubator for the developing infant is arguably the creature's most well-known physical attribute.