The Extragalactic Crustaceans hiding in The Grim Darkness of The Far Future

I'll be honest, I've wanted to write this little analysis/rant for longer than this blog has existed, years to be exact... But the more I want it the more terrified I become of how to tackle something like this.

Warhammer 40,000 is unlike any other fictional universe I know, not because of the themes or concepts it presents and explores (although those truly are unique to the setting) but rather the sheer and absurd amount of lore and world building details and events all shoved into a barely coherent chaotic mess of a universe that somehow remains largely consistent and to an extend follows its own internal logic for progression and pace.

To try and cover a single aspect of 40k without delving deep into the lore is both really easy and extremely... idiotically... impractical.

Luckily for me in the past 2 decades the only thing I actually do somewhat understand and follow about the 40k universe are (to no surprise) the Tyranids!

I was a late comer to the 40k craze. In fact saying I've been into the lore for 2 decades is a bit of a lie.

I've known about 40k since the early 00s but my knowledge extended only to the fact it has insectoid aliens that want to devour all life in the galaxy, so far so good, plenty of those back then. I won't hide I was a lot more captivated by the Zerg back then until StarCraft 2 changed their aesthetic and even philosophy in ways I could no longer feel ecstatic about. The slimy pulsating organic parasitic monstrosities of the 90s were replaced by... hairy beasts and exaggerated but still tame monstrous teeth and scales?

Then I finally took a closer look at the Tyranids and to my surprise they were what I was craving for now that the Zerg became way too predictable for me.

Any 40k fan would agree that the first time you dive into the lore you are overwhelmed to such extremes that you either back out screaming or brace yourself and go in deeper.

I chose neither.

I follow a certain philosophy, one that has robbed me of many professional and hobby related ventures but has kept my mental and intellectual capacity working in an organised and efficient manner since I was a little boy.

I never dig deeper than I need to at the moment.

No matter how appetising or seductive a topic or fictional universe is I never rush to taste it all at once.

Step by step, layer by layer, I slowly but steadily unravel whatever interests me, even if takes me years or decades to do so. Better to be immersed in something you love gradually and slowly than to burn out in no time at all.

And now I come to the reason for making this analysis.

The lore and details surrounding the Tyranids are fragmented, incomplete and worst of all absolutely contradictory... For every fact and solid information we are given there are hints of contradictions, falsifications and outright lies and deception. There is no definitive lore book I can point at for you to read and suddenly grasp everything about these insectoid monstrosities.

That is unless you can get your hands on Xenology.

As far as I'm concerned that is the quintessential piece of lore about the Tyranids even if it's outdated and probably not even official canon at this point... then again talking about what is or is not canon in 40k is an even stickier topic for debate.

So for my personal convenience and out of respect for my sanity I will mostly use the info we are given in Xenology for the analysis I want to share with you all today.

Tyranid Autopsy

by Adrian Smith

As both a fan of the Zerg and Tyranids I have a saying that I am particularly fond of: "The Tyranids are dinosaurs that want to be bugs and the Zerg are bugs that want to be dinosaurs".

Both insectoid races share a lot of similar traits and functions but the core difference is their consistency.

As I mentioned above the Zerg are slowly but surely become more reptilian and even mammalian while the Tyranids despite having a rather typical vertebrate body plan stick closer to their arthropodal traits.

In a way it's funny to see the race that outnumbers most other insectoid swarms in fiction both in sheer numbers and diversity of forms and lifestyles to be so universally consistent and follow a similar morphology while adding or reshaping it to the extremes to reach the ultimate diversification through endless adaptation. Kind of like arthropods of real have been doing throughout Earth's history.

That is to say Tyranids are in no way alike, even the question of what is or is not part of their "species" is something that cannot be easily explained or even hypothesised upon. Everything from the microscopic organisms that can be found inside each bioform, bioship or even deployed on a planet up to the gigantic towering living mountains of terror that are the massive troops of the Swarm are part of the collective. It's easier to think of the Tyranids as a whole mobile ecosystem than a single species or even phylum.

However for this analysis I want to do something different.

I created this blog in order to continue sharing my thoughts and views on any fictional creature that I feel fits into the overall arthropodal aesthetic or theme of design.

The Tyranids themselves are obviously quite insectoid in appearance and behaviour but instead of breaking down their individual designs and function I want to try something a bit sillier...

Comparing real life organisms with fictional ones is helluva fun, no one can make me think otherwise but I won't lie that it's both tricky and ultimately serves no real purpose other than to entertain and maybe teach a thing or two about the organism.

Saying that a fictional alien being is even comparable to a single group of real organisms raises more problems than anyone involved in the discussion would like to deal with.

Still... The Tyranids are crabs!

There I've been waiting years to write this... and it feels absolutely liberating!

Now with that click/attention bait out of the way, what do I mean by this?

Well I did say the Tyranids are insectoid, and they absolutely are.

But then again Pancrustacea is a thing.

And yes I am aware that is hardly an excuse to call insects crabs or even crustaceans but it doesn't really change what I am proposing here, which is that out of all the animal organisms on this planet I believe crustaceans are the closest, morphologically speaking, to the Great Devourer of 40k!

Once again I suggest you go grab a copy of Xenology somewhere (libraries still a thing?) and dig through all the info presented there as it goes into insane detail about the Tyranid morphology, very impressively so too!

What I can summarise for you is that the typical Tyranid bioforms (their troops basically) are hexapodal (possessing 6 limbs much like insects and other hexapods), have a rigid chitinous exoskeleton and a partial endoskeleton, are able to heal and repair the outer layers of their shell/cuticle by shedding parts (usually scales) and replacing them in a very similar manner to how arthropods moult, have a circulatory system that is neither fully closed or open, use something more similar to hemolymph for blood and posses both gills and what is essentially spiracles on various different places on their bodies.

Now the chitinous exoskeleton, spiracles, moulting and even cuticle repair is something insects posses.

Healing of injuries on the cuticle of insects is limited but present and the method by which cracks and tears are fixed is hauntingly similar to what is described for the Tyranids in Xenology. Basically the crack is sealed by depositing new cuticle layers in liquid form (the arthropod cuticle is non-living and easily replaced during moulting by secreting the new layers beneath the old ones before shedding the entire old shell and inflating the new one before it hardens into shape).

Tyranids also posses endoskeletal structures but most of those are indeed ingrowths of the exoskeleton, something again present in many arthropods including insects.

The only true endoskeleton inside these bioforms are the skull and spine (making them genuine vertebrates even with such a reduced internal skeletal system) but even those are hidden beneath the chitinous covering.

I also want to point out how ingenious it is to decide NOT to include any bones inside the limbs.

I've always had an issue with insectoid monsters having both exo and endoskeletons simply because it makes very little sense and actually harms the creature.

Any benefits brought by having an exoskeleton disappear the moment your giant bug monster also grows an internal skeleton, it doubles the weight of the creature while also diminishing most space inside the limbs which could have been used for muscles and better attachment points for them.

Arthropods are proportionally strong not only because of their smaller size combined with an exoskeleton but also because their limbs are practically hollow (somewhat) and provide better leverage for the muscles, once you add any rigid skeletal system inside those you defeat the purpose entirely.

So discovering that Tyranids are indeed vertebrates and have endoskeletons combined with exo ones was at first troubling but the way it was handled (at least in Xenology) is remarkable! The skull and spine serve as extra protection for the central nervous system while minimising weight and keeping almost all the benefits of having an external skeleton.

So far so good, right? Tyranids are insectoids through and through, so where do crabs come in?

Aside from the obvious gills which again some insects posses (entomology is wild and confusing... I love it) there is one more morphological trait given to Tyranids in several lore sources, a circulatory system that is both open and closed.

It's a pretty common knowledge that arthropods posses an open circulatory system seeing how they are primitive and underdeveloped animals that can't dream to achieve the complexity of the great mammals like ourselves!

True.

But also wrong.

Insects posses an open system, yes, but crustaceans exhibit something that is truly remarkable but also complicated to explain in any simple way.

So let me share the research paper that deals with this phenomenon.

The decapod crustacean circulatory system: a case that is neither open nor closed

Historically, the decapod crustacean circulatory system has been classed as open. However, recent work on the blue crab, Callinectes sapidus, suggests the circulatory system may be more complex than previously described. Corrosion casting techniques were refined and used to map the circulatory system of a variety of crab species (order: Decapoda; family: Cancridae) to determine if the complexity observed in the blue crab was present in other species. Seven arteries arose from the single chambered heart. The anterior aorta, the paired anterolateral arteries, and the paired hepatic arteries exited from the anterior aspect of the heart. The small-diameter posterior aorta exited posteriorly from the heart. Exiting from the ventral surface of the heart, the sternal artery branched to supply the legs and mouthparts of the crab. These arteries were more complex than previously described, with arterioles perfusing all areas of the body. The arterioles split into fine capillary-like vessels. Most of these capillaries were blind ending. However, in several areas (antennal gland, supraesophageal ganglion) complete capillary beds were present. After passing through the capillary-like vessels, blood drained into a series of sinuses. However, rather than being arbitrary spaces as previously described, scanning electron micrographs showed the sinuses to be distinct units. Most of the sinuses formed a series of flattened membrane-bound lacunae. This complexity may qualify the decapod crustacean circulatory system as one that is "partially closed" rather than open.

https://pubmed.ncbi.nlm.nih.gov/15683568/

To understand why arthropods "chose" to stick to an open circulatory system for so long one must realise where they originated.

Like all other life on this planet arthropods arouse in the watery depths.

In an aquatic environment having an open system is both easier and more efficient but it also helps dealing with low temperatures and high pressure, something many crustaceans of today still have to overcome daily.

But decapods such as crabs often live dynamic and energetic lives, both as predators and prey.

In order to keep the benefits of the open system but also gain the various boosts of having a partially closed one some crabs developed this unique partially closed circulatory system.

What does all this have to do with our space locusts? Simple! Tyranids spend a lot of time in the vacuum of space and are expected to be able to function in many different environments, from deep space to the surface of various alien ecosystem and even deep underwater, all places that require a more open and flexible circulatory system as opposed to a completely closed one.

So the Tyranids have developed a system quite similar to crabs, one that allows greater resistance to temperature and pressure changes as well as being as efficient as possible for beings of their morphological complexity and size.

Of course this hardly makes them crustaceans in the truest sense but it is the main component of their biology that sets them apart from insects and really most other arthropod groups.

Calling them insectoid is still the best choice as they are thematically and visually such, but I like to think of them as more... crabby.

And if you're still not convinced enough...

Well let me quote what Jes Goodwin said in an interview on the Tyranid Codex 4th Edition (2005):

To make them more ‘Tyraniddy’ rather than ‘Alienesque’. It had always been the intention to make them an expression of the Gribbly/B-movie alien Archetype, which the Alien, the Predator, the Thing, the Metaluna mutant are all expressions of rather than being archetypes themselves. I also wanted to play up the Reptilian/Dinosaur/Crustacean elements to get rid of the ‘insect’ tag, Tyranids should look like an amalgamation of lots of different species, you shouldn’t be able to pigeonhole them easily [The original brief for them at the time of Rogue Trader was for 6-limbed, bio-engineered dinosaurs in space]