Xeno- and Neomorph mass

from my understanding the chestburster feeds on its hosts blood supply and would probably releases a form of pain killer while gestating before its born

Well they are Totally Alien and Made Up Organisms/Parasites so some Science goes out the Window.

I am not sure if there is any Material that Details the Chest Buster and its Process, i have not read the Weyland Yutani Report so i am not sure how much information is given in that Book.

The Chest Buster Embryo is something that gets Changed a bit in some Movies, such as Gestation Time etc, in ALIEN the X-ray seemed to show a Black Mass and not really any Embryo but this was at a Earlier Stage.  This kind of Fits in with Alien Covenant and the Neomorph Infection (Mass/Cloud of Tiny Parasites that then go on to Create the Embryo that Grows).

But from ALIENS on wards it seemed to be the Status Quo that some kind of Embryo was Implanted.  

The Franchise would seem to show that the Face Hugger would implant something, be it Embryo or a Tiny Parasites/Pathogen that would Form to a Embryo, the Face Hugger seemed to keep the Host Alive by Acting as some kind of External Lungs.

As the SEED if you would Gestates, we assume it is Obtaining some DNA from somewhere which it Encodes into its Genetic Make Up to take Traits from the Organism, but it also would have to take some Nutrients from the Host. It is likely the Embryo gains Nutrients from the Lining of the Lungs like a Normal Embryo would from the Endometrium of a Uterus, before at a Certain Stage (after the Face Hugger disconnects its Breathing Apparatus from Supplying the Bronchus) it can maybe Connect to the Blood Supply that goes to the Heart

I think it likely releases some Immune Suppressant too so that the Body does not Reject or Attack the developing Embryo as well as Enzymes or similar that effect the Nervous System so the Host can-not feel anything Growing inside.

Alien Covenant confuses things because of HOW QUICK the Gestation seemed and also with Lopes infection the Face Hugger was not required to be Attached in order to have any EFFECT on the Embryo.

The Neomorph seemed a WHOLE different Kettle of Fish we can only Speculate that the Nano Parasites either only Needed ONE to connect to a Blood/Nutrient Supply in a Host and Grow (Cell Multiply) from this (or inject its Payload that begins the Cell Production/Multiplication) or if the Parasites would Clump together and Join like Cell Multiplication. 

Again the Parasite being able to Take Nutrients to Grow and DNA at a Super Accelerated Pace.

I would add the Neomorph seems Superior to me as far as Procreation, if you could Genetically Engineer a Neomorph to gain some more Traits that would make it Tougher and Stronger i would see the Xenomorph as Inferior.

We dont see the Neomorph as having Acid Blood which is a Advantage for the Xenomorph.

Which i Forgot... i think its likely the Xenomorph when ready to Chest Burst may release some Acid to Weaken the Chest Wall to make for a Easier Chest Bursting.

  If drawing the required mass so rapidly from inside their host, Kane should have been feeling pain a lot earlier and an autopsy on Ledward should have shown more internal mass missing too.

would probably releases a form of pain killer while gestating before its born

I think both of these are good points. And lets not forget a couple other things. Kane, having been feeding a rapidly growing parasite should have looked even weaker than he appeared and should have had difficulty breathing far earlier from having his lung capacity diminished so much. 

Interestingly, as the buster grew, the host should have had more trouble supplying oxygenated blood as the creature grew because of its own growth. By the time it was ready to burst, Kane's entire cardiovascular system should have cut off all blood/oxygen to the brain and he should have just collapsed instead of thrashing around. Oh well- still gotta love that iconic scene!

What impressed me about the original Alien was that the alien was GENUINELY alien. Acid for blood, very rapid growth, etc. Giger seems particularly interested in bubble forms (rounded, as if pressurised from within) so for me, the problem of rapid growth is easily explained by the alien being mostly exoskeleton: I imagine a very low density fibrous structure inside. Did you ever see the movie Shin Godzilla? Could that be a very similar concept: not just a large lizard, but a radically different concept of life? In the case of Shin Godzilla the body seemed to be held together and moved by atomic energy – that is the force that not only stopped the being from collapsing under its weight, but could even burst out from the body, and rapidly reconfigure the physical shape. I was particularly interested in the very end where the humanoid creatures began to break from the tail, suggesting that the whole body was made from a web of fibres, filled with plasma and space, rather than solid bone or muscle. In Prometheus, the black goo worked so quickly that I wonder if something similar was going on. That is, is the life force best thought of as fibre and energy rather than solid blocks? It might use a host body, but only as a parasite uses a superstructure: once it has sufficient materials it becomes a shell with low density fibrous inside. Now low density does not have to mean weak or soft: it might be like drums of steel mesh inside: a drum of steel mesh is extremely strong even though most of it is air. Or it could be aerogel – filling the space with no gaps yet being almost as light as air.

Whatever the biology, if the blood is molecular acid then the body must be fundamentally different from the usual human form. Maybe the acid is only created by injuries – that is, two substances are kept apart, but if the skin is cut they mix and create the acid. Or maybe the body makes use of the acid through some very unusual reactions. Either way, a low density body seems possible. As far as I know the aliens require a host in order to grow, which suggests that the final form may be extremely unusual: otherwise, why not just grow on its own using regular food? But my guess is that creating the final alien form requires all the complexity of a regular body to feed it, much in the same way that an electronic brain requires a biological brain to create it, but once created it can link an entire planet and do things that a biological brain cannot even imagine.

Just thinking aloud!

im sure the neomorph does have acid for blood as we saw with walter shoving his hand inside the mouth of the neomorph that attacked him and his hand melted didnt it?

i might be wrong its been a while since i watched it.

Well it kind of  Looked that way, as Walters Hand did look like it had Melted a Bit, but then its a Case of HOW did David replicate that (but the Crew maybe would not have paid a Great lot of Attention to his Wound).

However during the Shooting of the Neomorph by Oram we NEVER really saw any Evidence of Acid Blood.  Which is a bit ODD as the Hammerpedes had Acid Blood, and it was likely the Trilobite did too (as the Full Scene it would appear the Engineer obtained his Acid Burn from Biting the Trilobite but we DONT have that Full Shoot not even on Extras).

As David and Dr Shaw had taken the Juggernaught from another Complex, maybe this Complex has a Different Kind of Black Goo that does-not pass on the Acid Blood, but David was able to add this to his Final Specimen?

Looking at the ACID BLOOD and in reply to Nathan, then maybe the Chemical that is the Blood would React with the Air and so WHILE the Blood is inside the Organism it does-not have the Acid Properties but it does so ONCE the Blood leaves the Body?

But it is more Likely the Genetic Structure of the Xenomorph is NOT affected by the Acid.

There was a lot of potential with the creature. I liked actually that it stood up in front of david and was mesmerized by him somehow. David not being a lifeform somehow causes it to see no threat or reason to attack it McDVOICE

It's possible that the neomorph can rapidly secrete a highly acidic form of 'saliva'. As BigDave mentions, David's wrist looks melted. You can clearly see a burn mark on his sleeve.