Chestburster (Earth-9471)

"In a few hours it's gonna burst through your ribcage, and you're gonna die. Any questions?"

- - Ellen Ripley to Larry Purvis

The Chestburster is the third stage of the xenomorph evolution and the speciies' infant form. The creature is infamous for its horrific gestation - after being implanted into a host by a Facehugger, it matures within their bodies, mutating into a cancerous body that eventually erupts from the host's chest with extreme violence and trauma.

Anatomy and physiology
Chestbursters are small, reaching only 2' (60,48 cms) from their head to their tail. They resemble massive worms, being beige or brown in color as opposed to the black and bluish mature xenomorph forms. They possess two dimunute arms which later develop as they grow older, and which can vary between forms, notably Queen Chestbursters, who are born with all of its four extant arms and legs present. While the reason for the differences remain unknown, it has been theorized that some hosts die prematurely duo to the Chestbuster's nature as an invasive organism, prompting the Chestbuster to be unable to escape from their bodies in time.

Within the body of their hosts, Chestbursters are attached through small umbilical cords that gather nutrients necessary for their growth. Because of the xenomorph super cell, the Chestburster acquires some of the genetic traits of its host via the DNA Reflex.

Gestation
Chestbursters are introduced into their hosts through a Facehugger. Once the Facehugger attaches itself to the host, it inserts the proboscis down to the victims's throat, which supplies them with a suitable atmosphere for continuous breathing, as well as the implantation of the xenomorph embryo into the victim's esophagus. The process wildly vary in time, ranging from several hours during the Feral Stage to mere minutes during the Coordinated Stage and beyond.

In fact, Chestbursters are not literally embryos, instead being a parasictic organism that deposits a tumor at the chest cavity of the host, which consists of a series of tailored cancers that restructure the cells of the host, assembling a Chestbuster. The implantation, much like the process, can vary in time, from a few hours to several minutes depending on the xenomorph stages and evolution. During the Feral Stage, it is theorized that the Facehugger detaches itself from its host after receiving a recombinant plasmid pulse from the Chestbuster. In later stages, it is likely that the Queens telepathically commands them to do so. This process is very complex, requiring the absorption of the host's organic material, which is then broken down in a molecular level to be rearranged as new compounds. Carbon units are then disassociated and quickly recombined into crystalline lattices, all of which are used by the Chestbuster to form its hard exoskeleton. The freed H+ ions are merged with surplus sulfate (SO42-) and nitrate (NO3-) to generate the xenomorph's acidic blood. Because of the resulting xenomorph super cells at work, the genetic material of the host is passed down to the Chestburster, and vice-versa. This trait allowed Weyland-Yutani Corporation scientists aboard the USS Auriga to clone the the Queen that was gestating within Ellen Ripley.

The develop of the host's characteristics within the Chestburster dictates the future appearance of the adult xenomorph, and ONI scientists have observed the "embryos" copy 10-15% of the genetic code of their hosts through a process they dubbed the DNA Reflex. As the "perfect killing organism", the genetic absorption is part of the xenomorph's incredibly adaptability to any environment they are born, also helping to "cover" from the immune system of the victim. The DNA assimiliation allows for several physical variety and diversity when the xenomorph reaches their adulthood. Notably, a Chestburster born from a sangheili will sport the species' signature four mandibles, while quadrupedal hosts, such as dogs, will birth quadrupedal xenomorphs. It has been since theorized by Weyland-Yutani that the final intelligence and instinct of the born xenomorph may be influenced by their hosts.

During the growth process, the hosts do not experience any obvious negative systems. Instead they start building up acutely after the Facehugger dies and detaches itself from the host's face. The most common symptoms are sore throats, nausea, increased congestion, moderate to extreme hunger. Chestburster Keyminds may cause additional symptoms, including shortness of breath, extreme exhaustion, internal hemorragia, chest pain and finally nightmares and hallucinations.

Chestbursters grow rapidly; for example, the inner jaw of the xenomorph forms within an hour. The gestation process wildly varies between the stage the xenomorph species is present. During the Feral Stage, it range3s from an hour to a full day, while during the Coordinated Stage, it can range from mere minutes duo to the higher calcium and influence of either a Keymind or a Gravemind. However, the physical defects in a host can affect the development of the Chestburster. Notably, Larry Purvis were both impregnated with Chestbursters by Facehuggers but had their gestation process take longer than usual; Jenkins was an avid smoker, while Purvis suffered from a thyroid defficiency.

Emergence
Once they finish development, Chestbursters releases enzymes that reduce bone to brithe-like composition and its surrounding tissues to ease its emergence, before it finally forces its way through the victim's sternum. The host experiences discomfort in the minutes leading to the emergence, such as nausea and chest pain. The actual emergence is very quick, but brutal, and the Chestburster exit from the chest within seconds. It starts with cramp-like pain in the chest of the victim, progressing to severe agony and uncontrollable convulsions. When the Chestburster emerge, death is near instantaneous and painful, with the victim experiencing massive trauma, blood loss and organ ruptures, all at the same time.

The Chestburster is the most vulnerable stage in the life cycle of the xenomorph, possessing little to no defenses outside of its acid blood, which the infant creature cannot use with extreme precision. When born in an area with other individuals, Chestbursters will try to escape instead of attacking, preferably in areas where others cannot reach them, such as holes, caves, ducts and vents; when none of these are present, a Chestburster will dig a hole with its own blood to run away. While they are capable of killing other lifeforms, they are severely limited alone and without the presence of higher xenomorph intelligence.

The impact the emergence of a Chestburster has on a victim had an adverse effect on the species, with victims seeking to commit suicide or ask others to do so before they endure the traumatic pain and violence of the creature's birth. These actions can be deadly to the Chestburster depending on the area the host kill themselves. Cryosleep can halt the development of a xenomorph and prevent their birth, such as was the case with Corporal Teresa "Tequila" Aquila, who was placed in a cryo chamber by Amir "Bacon" Kinard to save her from death.

While they are small compared to their xenomorph brethrean, Chestbursters are incredibly strong, and their emergence is not halted by dense and thick materials. They are perfectly capable of bursting through M3 Pattern Personal Armor.

Growth
After they emerge from their host's body, Chestbursters will develop very quickly. The Alien was able to reach maturity within hours after its birth aboard the USCSS Nostromo. ONI scientists aboard the USS Auriga noted that the development of a Chestburster was even perceptible to the human naked eye. There, Dr. Carlyn Williamson noted that Chestbursters expelled a viscid foam through their body during the growth process. Chestbursters start shedding similar to reptiles during their development, a sign of that full mature xenomorph is nearby.

Survivability
The birth and emergence of a Chestburster is inherently fatal, although there have been claims that the creature can be safely removed without side-effects on the host. This has been proven false by the forerunners in the past, and later by human scientists who discovered that, even if the embryo is safely removed from the host, and thus allowing the brutal emergence to not occur, the victim would still die from a series of terminal tumors that the xenomorph super cell developed while mutating the body of the host.