8.1 A Possible Starting Point
8.2 The Process of Exoskeletal Growth
8.3 The Incorporation of Iron
8.4 Developmental Rate
8.5 Open vs. Closed Circulatory System
8.6 Hyper-Stable Collagen Variants and a Wide Range of Uses
8.7 Possible Timelines For Exposure to Low pH Substances

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A Possible Starting Point

We begin to see the first viable option for the construction of an I. raptus exoskeleton by working within the understanding that the vast majority of eukaryotes employ a multilayered dermal structure that is comprised largely of proteins. The current working model for the Alien revolves around the utilization of a “hyper-stable fluorinated collagen variant” (also known as a “collagen mimic”). This is similar to what has been employed by the scientific and medical communities since the first half of 21st century as a structural bio-stabilizing protein. This model also sees the pattern of growth for the Alien's exoskeleton as similar to that of byssal threads (as produced by Terran mussels). However, to further understand this theory we must first understand collagen, its acceptance of Fluorine and its use in byssal development.

Collagen
Collagen is one of several structural proteins found in the vast majority of eukaryotic organisms. It has great tensile strength, and is the main component of ligaments and tendons making it the primary protein of connective tissue. It is also responsible for skin elasticity. Collagen is the most abundant protein in mammals. Among humans collagen makes up approximately 25% of the protein content within the body - aside from connective tissue it's fundamental in the construction of bone, skin, scar tissue, and teeth. Collagen also has a very interesting amino acid composition: it contains a great deal of glycine and proline, as well as two amino acids that are not inserted directly by ribosomes - hydroxyproline and hydroxylysine. The former composes a rather large percentage of the total amino acids within the protein. Both are derivatives of proline and lysine in enzymatic processes of Post-Translational Modification, for which vitamin C is required.

The white collagen found in the majority of connective tissue among mammals consists of interwoven fibers of the protein. These fibers are comprised of globular units of the collagen subunit: tropocollagen. Tropocollagen sub-units spontaneously arrange themselves under given physiological conditions into structurally staggered arrays, which are stabilized by numerous Hydrogen and covalent bonds. Tropocollagen sub-units are known to be left-handed triple helices in which each strand is further, a right-handed helix unto itself. Thereby making tropocollagen a “coiled coil.”

Another feature of interest in collagen is that it has a regular arrangement of amino acids in each of the alpha chains of the collagen sub-units. The sequence generally follows the pattern of Gly-X-Y: X is proline, and Y is proline or hydroxyproline. There are very few other proteins known to current science with such regularity. The incredibly high number of Gly residues allows the tight coiling of each of the alpha chain subunits of tropocollagen. This gives a rise per turn of 0.3 nm as opposed to the 0.36 nm found in a standard Alpha helical coil. Hydroxylysine and hydroxyproline play key roles in the stabilization of the tropocollagen globular structure as well as the final fiber shaped by forming covalent bonds. The resulting structure is known as a "collagen helix."

As for the addition of Fluorine to create a “hyper-stable collagen variant “(or collagen mimic) the hydroxyproline residue, characteristic of the triple repeats normally found in native collagen, is replaced by fluorinated proline residue. In collagen's common state, the polymeric hyroxyproline is created via the proline's interaction with excess oxygen and Vitamin C. In the case of I. raptus this would be excess fluorine. The potential presence of Hydrofluoric acid within the creature's body could lead to the creation of a fluoroproline This resulting molecule would bond with the base proline and entwine glycine to form the necessary polymer. The creation of a Fluoroproline in place of hydroxyproline also eliminates the need for Vitamin C because this molecule now relies on the presence of elements already in the Alien's physiology. And because Fluorine so readily replaces hydrogen in many instances it is possible that we may see the additional creation of a Fluorolysine as opposed to the common Hydroxylisine. The end result is a hyper-stable variation of collagen which has an increased strength, chemical inertness, and heat resistance - thereby creating a collagen-based protein whose life span is extended considerably via the neutralization of standard denaturalizing time lines and conditions. Such a variant is able to withstand exposure to much higher temperatures, greater pressures, and various reactive agents for much longer periods of time before chemical breakdown – Something that is consistent with the Alien's exoskeleton on numerous recorded instances.

Byssal
Byssal threads - which are strands of collagen - are among the strongest natural adhesives known to man. The manner in which these strands bind to any substrate (natural or synthetic) is unparalleled among carbon-based organisms. And at 5 times stronger than a human tendon, and 16 times more extensible, a single byssal thread weighs in as one of the strongest natural protein fibers known to man – next to spider silk. However, as strong as these strands are mussels do not rely on a single thread to anchor themselves to an object – numerous threads are formed to create a byssal mass. The relative strength and tensile resilience of the mass increases with the addition of each thread, thereby creating an incredibly durable protein net.

The initial base for byssal growth is a mucus-like fluid that is a first excreted via the mussel's foot. From here the byssal threads are formed as the fluid solidifies. A fully formed thread is comprised of two distinct forms of collagen: Col-P and Col-D. These are distributed in a complimentary gradient with Col-P being most predominant in the elastic region near the foot of the mussel, and Col-D located at the further distal end. Precursors of Col-D and Col-P are found in the mussel's foot - the preCol-P contains three major domains - a tough collagen-based domain, flanked on either side by a pair of elastin-like regions. These stretchy domains are in turn flanked at each end by sections rich in the amino acid histidine. Also present, but in slightly lesser degrees are Glycine and Alanine.

Located at each end of the preCol-P the histidine is what actually helps create the incredible strength of byssal threads. Whenever histidine-rich domains occur in proteins, they usually bind with metal. In human blood histidine-loaded glycoprotein binds with zinc. In byssal threads these domains react with iron to produce incredibly strong bridges, which link up linear arrays of collagen, and should a break occur in any of these cross-linked sections it is promptly repaired. It is iron that also causes the threads to form and solidify. As iron from the surrounding seawater is absorbed it's quickly incorporated into the pre-byssal formations.

Byssal threads have the amazing ability to bind to any man made or natural surface: including plant fiber, animal tissue, glass, Teflon, as well as other byssal threads.

In the early 21st century contemporary science was able to reproduce this material. Since then it has been utilized by the medical community in sealing incisions, “pinning” broken bones, applying cells to tissue substrate, and numerous other medical aspects due to its extreme strength and biocompatibility. Because of its organic nature and biocompatibility it is not a pollutant, therefore it does not cause toxicity within a receiving organism, nor is it detrimental to a given physiological environment or natural ecosystem.

Collagen also has the interesting trait of developing in relation to the amount of heat available to it in a given environment: it's optimal range for development and growth is between the 15° C and 37° C range. Growth will often occur at temperatures outside this range, but the most significant growth can be seen here. When looking at this information with regards to byssal thread production we see a unique development: Mussels that are kept in temperatures ranging from 15° C to 30° C (one degree below the lethal limit for the organism) byssal thread production underwent a two stage process. The first stage being an accelerated growth rate of Byssus, which lasted 1 to 7 days. In the second stage the Byssus development time is reduced, and lasts up to 21 days. Mussels observed in seawater ranging from 14° C to 5° C show a different rate of Byssus growth: there is no stage of accelerated growth – all Byssal Threads are formed at a reduced, yet consistent, rate. It has also been observed that mussels in colder climates require extended periods of time to generate a byssal mass of equal size and density to those mussels located in warmer climates.

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The Process of Exoskeletal Growth

It is the current belief that I. raptus employs a highly Fluorinated hyper-stable collagen variant in the construction of its exoskeleton. Following what we know of byssal threads and their growth and development it is also believed that this exoskeleton is constructed of a dense network of interbonded byssal-like fibers, thereby enabling the creature to have a incredibly strong, yet resilient epidermis capable of withstanding flexure stress, weight support, fluid movement, and highly reactive chemical compounds such as Hydrofluoric acid.

The working concept of growth and development for this structure is as follows: being a collagen mimic the protein is able to develop and amass within a host with little to no adverse, or outward, effects to said host. The protein is able to grow within a relatively neutral environment, such as that of a mammal, or the interior of an I. raptus egg, and not require the surrounding material to come into contact with the potentially hazardous/toxic internal chemistry of the Alien. This also allows the internal chemistry of the Alien to develop separately from the external, thereby never endangering the host organism or itself via the host's immuno response to reactive and toxic biochemistry.

The first, and innermost layer of the exoskeleton, is believed to be a Fluorinated unsaturated hydrocarbon. This particular structure, though not very rigid is believed to be the core element responsible for not only bioelectric dispersion throughout the body, but also for the suppression of detectable thermal signatures. The incorporation of the halogen Fluorine with this type pf hydrocarbon creates a polymer that is chemically inert (thereby making it virtually immune to reactive substances), it acts as a thermal shield, and is able to generate and conduct free electrons as a result of contact with external sources of radiating energy.

The second layer, referred to as the I. raptus equivalent to the stratum germinativum, is believed to be a thin viscous material from which amino acids are formed and eventually develop the collagen mimic precursor. As the protein forms and matures iron is introduced, which forces the production of strands similar to those found in byssal mass. As the strands solidify they move outward - ultimately forming the outermost layer of the epidermis.

Based on limited data from the Nostromo and the Auriga it is believed that the chestburster's epidermis is similar to that found on the Facehugger: a protein polysaccharide sheath - which is rapidly replaced by a layer of polarized silicon. This variation in epidermis between the hatchling Alien and the adult is believed to be a result of the collagen-like exoskeleton requiring a suitable substrate to bind to prior to initial development. The protein polysaccharide sheath, though an acceptable formation for byssal-like bonding, is structurally less sound than the layer of polarized silicon. It also allows for the required polarization based on variables present in the surrounding environment at the time of the Alien's birth, which in turn is believed to aid in the accelerated growth of the exoskeleton.

The average time frame of development of the hatchling Alien is so advanced that it's believed that the creation of a silicon skin begins moments after birth. The polarization of this skin allows specific electromagnetic energy to pass through, while deflecting all others, thus allowing the hatchling to absorb only that energy which is beneficial to its development and the generation of its own bioelectric output. All living organisms, as well as electronic devices emit electromagnetic fields – in most cases these fields are too slight to cause any natural or mechanical interference, but it has been recognized that various organism will react to these fields – even if it only generates a slightly different behavioral response. It is believed that the Alien is much more sensitive to these fields and is able to utilize them in such a way so as enhance and amplify it's own bioelectric output. It is theorized that for the first 20 to 30 minutes of life the newborn Alien is absorbing the necessary electromagnetic energy needed to sustain the bioelectric and metabolic maelstrom that will ensue, and which ultimately causes further development into adulthood.

As the external electromagnetic fields come into contact with the sub-dermal Fluorohydrocarbon layer free electrons are released in response to the stimulus. This release of energy then generates additional energetic output - which, in turn, causes the release of additional energy. This cyclical response in conjunction with the incoming electromagnetic energy generates an ever-increasing level of bioelectric output. This energy is then used in the generation of cellular material through out the body. The continual increase in bioelectric energy is believed to culminate and eventually cause a massive burst of bioelectric output which lasts anywhere from 30 to 45 minutes. It is at this point that the most dramatic exoskeletal formations occur. Prior to this the exoskeleton is believed to exist as a pre-skeletal formation beneath the polysaccharide epidermis: a thin layer of densely arranged collagen variant fibers that exist in a state that is firm enough to offer support and structure to the young Alien, but soft enough to leave the creature in considerable danger if left out in the open for too long. This softened pre-skeletal formation may be a result of aiding in the absorption of electromagnetic fields. If the pre-skeletal structure were more densely constructed these fields would not have the desired level of intensity once they penetrate the creature's skin, thereby causing the process of growth and development to slow down considerably. It should be noted here that the head is a probable exception to this: due to the force needed to emerge from the chest cavity of a host the pre-skeletal structure would not bear the required strength to free the young I. raptus from it's “womb”. The cranial structure is believed to be much more developed – possibly even “over developed” in comparison to the rest of the creature's anatomy. This is thought to be analogous to the “egg tooth” that many egg laying reptiles have at birth. The sole purpose of this tooth is to pierce and tear the egg shell so that the young reptile can free itself. A noted exception here is that this tooth is lost early in a reptile's life, where as the cranial structure of the Alien is retained and continues to develop.

As the exoskeleton develops the tensile abilities of the young Alien's silicon epidermis are pushed to their limits, eventually causing it to split. Based on records form the Nostromo and Furina 161 it would appear that this split occurs along the entire vertical axis of the dorsal surface – possibly starting in the region of the cephalathorax and continuing downward over the tail with minor lateral splits occurring along the abdomen. This would also remain consistent with various organisms, such as arachnids and insects, which are known to shed in a similar manner.

Once the silicon epidermis has split it sloughs off and is quickly discarded. The continued growth and development of the exposed exoskeleton progresses, matching the growth of the Alien's internal structures until it ultimately bears the form that is widely recognized, and associated with in regards to I. raptus. Exoskeletal growth and development continue once the Alien has reached it's full size, but it is considerably slowed. This is seen as being analogous to byssal thread and mammalian hair growth: the means to produce additional protein is present, but production is reduced to the point of falling into a rest period – only when damage is sustained, or portions of the exoskeleton age and need new growth does the production of new protein rise from a rest period to an active period. Because of the Alien's apparent natural efficiency it is believed that protein production for use in regenerating damaged exoskeleton is a relatively restricted process – occurring only in the areas that require new growth. And between Collagen's natural abilities to aid in regeneration and the Alien's apparent abilities to grow and develop at a remarkable rate it is no surprise that regeneration is believed to occur within hours and fractions of hours as opposed to the standard days or months.

The end product is believed to be an exoskeleton that is constructed of a dense mesh of inter-bonded collagen variant fibers. In order to maintain the strength and resilience recorded throughout the numerous encounters with humanity this protein mesh would not need to be exceptionally thick. The natural strength and resilience of the byssal-like fibers are enough to offer a great level of benefit while remaining relatively thin and light weight (the use of the word “thin” is a relative term when compared to the proportional needs of a chitin-based exoskeleton which would need to be many times thicker).

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The Incorporation of Iron

As with byssal threads it is believed that the strength of the Alien's exoskeleton is due to the incorporation of iron. On Earth, mussels pull iron from the surrounding seawater and then use it as a key aspect in byssal formation. It is believed that I. raptus also pulls iron from its surroundings, but the way this is done may vary depending on the stage in the Alien's life cycle. The first method is via the host. While the embryo is forming, and because its initial formation is done as a result of the reorganization of host cellular material, it is very likely - and quite possible - that not only is iron incorporated into the Alien's biology as it develops, but a considerable store of the element is acquired as well. This store would then be used to aid in exoskeletal development as the Alien transforms from hatchling into adult. This is considered extremely probable given the fact that the carbon-based life forms rely on the incorporation of iron as part of their physiology. The second means of acquiring iron is through ingestion.

Iron is the tenth most astronomically abundant element – which means that odds are very low that the Alien would ever find itself in an iron-deprived environment. As such it is very likely that the Alien would be able to supplement its need for iron by consuming various aspects of its environment – this includes organic and/or inorganic substances. It should also be noted that all five recorded encounters with I. raptus have shown that the Alien appears to favor iron-rich environments. Aboard the Nostromo the adult Alien (and its freshly shed skin) was first encountered in close proximity to the ship's mining and collection vehicles – vehicles that had just recently been used in iron ore extraction. These vehicles – though scheduled for routine maintenance and cleaning – were likely to have retained residual iron ore deposits. The Nostromo, itself, was nothing more than a tug for a large iron ore refinery (however, it should be noted that it has never been confirmed the Alien ever left the Nostromo and traveled to the refinery). A great deal of the Nostromo's structural elements, as well as large portions of the mining equipment, were constructed of tempered steel – which is an alloy composed of carbon and iron (carbon being another element believed to be an integral part of the Alien's dietary needs). We see a similar pattern on LV-426, Fiorina 161, and the USM Auriga: all of which relied heavily on the use of tempered and poly-tempered steel. Fiorina 161 also employed a rather archaic system of cast iron piping for portions of the facility's pluming – as was reported in areas on the creature's lair.

It should also be noted that iron is essential to all carbon-based life forms – with the exception of a few specific forms of bacteria. It's incorporated into the heme complex, an essential component of proteins involved in redox reactions – such as respiration. Inorganic iron is also prevalent in the iron-sulfur formations of many enzymes, such as nitrogenase and hydogenase. A class of non-heme-iron enzymes are responsible for a variety of functions within several life forms, such as methane monooxygenase (responsible for oxidizing methane to methanol), ribonucleotide reductase (responsible for the reduction of ribose to desoxyribose; DNA biosynthesis), hemerythrins (responsible for oxygen transport and fixation in marine invertebrae ) and purple acid phosphatase (responsible for the hydrolysis of phosphate esters). This then includes all carbon-based life forms within the scope of satisfying the Alien's dietary needs – which may help explain the creature's occasional carnivorous tendencies (as recorded on Fiorina 161) – this is discussed in greater detail in the Feeding Habits essay.

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