Bio-Titan

A Bio-Titan is a monstrously large Tyranid biomorph intended to counter the greatest war engines deployed by the other intelligent species of the Milky Way Galaxy. Towering above the battlefields, leading the swarms of lesser Tyranid creatures, stand the vast forms of the Bio-Titans. These massive biomechanical war-machines stalk the warzones of the Imperium spitting death and destruction, cutting down their foes with potent bio-weapons. Their approach is a terrifying sight to behold as they rip apart buildings, tear to pieces infantry and tank formations and even destroy Imperial Titans, Eldar Wraithlords or Ork Gargants with their armoured claws and ripper tentacles. Propelled relentlessly forward on their powerful legs, these horrifying creatures smash enemy defences into rubble with their deadly arsenal of bio-weapons. In return their enemies can do little; even under the heaviest fire, Bio-Titans are notoriously hard to kill as their huge bodies are protected by ridged plates of chitinous armour, and even when a lucky shot does penetrate their armoured sides a Bio-Titan is capable of rapid tissue regeneration.

Carnifex/Dominatrix Strain

 * Hierophant - The Hierophant Bio-Titan is an immense, hideous creature, towering over the battlefields and bristling with spines, tendrils and symbiote weapons. They are amongst the largest biomorphs yet encountered by the forces of the Imperium amongst the swarms of the Hive Fleets, comparable in size and power to an Imperial Titan. A brood of Hierophants are likely to be at the forefront of a major Tyranid attack -- striding forwards, drawing enemy heavy weapons fire away from the lesser creatures of the swarm, absorbing huge amounts of damage before smashing into the enemy line with devastating force. The Hierophant is the Tyranids' largest shock trooper, armed with monstrous Bio-Cannons, multiple claws and razor-sharp blades, and armoured with a thick chitinous hide that exudes poisonous spores from rends in its plates. Like all Tyranid biomorphs, the Bio-Titan seems to be able to mutate rapidly, evolving new weapons and defences. Other variants of the Hierophant biotitan have been identified with huge crushing claws or long scythe-like blades, cluster spines and other bio-weapons. The development of such large bio constucts remains mystery to the Imperium's Biologis. Whilst it seems a Hive Tyrant or Carnifex could easily be the result of a further genetic manipulation of the basic Tyranid Warrior genotype, there is no known genetic antecedent among the existing Tyranid biomorphs for the Hierophant. It is speculated by the Magos Biologis of the Adeptus Mechanicus that the Hierophant was derived from the combined genetic strains of the Tyranid Carnifex and the Dominatrix. The forces of the Imperium have learned that combating Hierophants is simply a matter of applying the heaviest firepower available; large ordnance weapons and heavy artillery have so far proved the only effective weapons in destroying Bio-Titans.
 * Tyrannofex - The Tyrannofex is a massive Tyranid Bio-Titan that exists purely to spread destruction to the Hive Fleet's foes. Created for service on the most grueling battlegrounds, the Tyrannofex is clad in a dozen layers of ablative chitinous armour and supported by three pairs of massive legs, and it is as unyielding as any war engine constructed of steel or born of more conventional technology. The Tyrannofex has the armour and fortitude of a living battle fortress and its bio-weaponry eclipses that of its foes' most powerful main battle tanks in both quantity and destructive potential. Worse, its body houses several breeding chambers, nurturing all manner of ferocious Tyranid organisms that it can unleash onto any enemy foolish enough to come too close. Its main weapon is a massive Bio-Cannon fused with its torso, the largest and most destructive of any of the Tyranid bio-weapons carried by a Bio-Titan. The precise nature of this weapon is different from creature to creature. Each represents a particular pinnacle of Tyranid bio-weaponry and is as efficient as it is unearthly in its design. It is speculated by the Magos Biologis of the Adeptus Mechanicus that the Tyrannofex, like the Hierophant, was derived from the combined genetic strains of the Tyranid Carnifex and the Dominatrix.

Ravener Strain
It is speculated that the Exocrine, Mawloc, and Trygon Bio-Titans are genetically derived from the Ravener subgroup of the Tyranid Warrior genus.
 * Exocrine - The Exocrine is undoubtedly the most specialised of all the Tyranid war machines, bred for the purpose of striking at the foe from long range while more conventional Tyranid bio-constructs close in to attack with tooth and claw. The highly developed forelimbs of other Tyranid creatures appear to be absent from the Exocrine body form, but the distinctive bony head frill and long tubular Bio-Cannon were originally the creature's forelimbs. These have fused together and expanded considerably to achieve their new purpose. The Exocrine fires high-velocity chitin shells, which with the aid of their silicon-based penetrator core, can punch through even Titan armour with ease. The shells are simple but deadly, penetrating the target and releasing an acidic slime fungus which replicates rapidly and cause severe damage to complex electronic and mechanical systems. More short range destruction is supplied by outgrowths of virulent spores on the creature's carapace. An autonomic nerve function fires in the presence of non-Tyranid bioforms with the speed and hitting power of Bolters. Exocrine are driven by instinct and are liable to become confused and uncoordinated unless they are tightly controlled by the Hive Mind. The Exocrine's natural instincts have been genetically altered to make it enter a nesting state, remaining stationary and hurling its chitin shells at the nearest enemy.
 * Mawloc - A Mawloc is a huge worm-like creature with massive razor-toothed maws that serve as the entryway to its equally cavernous gullet. These loathsome creatures are outriders to the Tyranid swarm, burrowing deep beneath the ground to bypass the enemy's front-line defences. Once past the outer perimeter, a Mawloc bursts forth in a shower of dirt and shattered stone to run rampant through supply lines, command posts or artillery batteries, only to vanish back below ground as forward units are recalled to the fight. Severe tremors are the only warning of a Mawloc attack, making defence duty a particularly harrowing experience. Most of a Mawloc's victims are swallowed whole, to be painfully digested within its body cavity. Anything too large to swallow is pounded flat by the Mawloc's muscular tail before being devoured.
 * Trygon - A Trygon resembles a much larger version of a Ravener. This vast serpentine creature is so colossal, that it even towers over the mighty Carnifex. It is heavily armoured, covered from head to tail with a carapace of shifting plates. A Trygon's claws are fearsome weapons in close combat, but they also allow it to burrow through practically any material. The Hive Mind uses the Trygon to excavate a massive network of underground tunnels so that other Tyranid creatures may use these tunnels left in the Trygon's wake, scuttling unseen to strike their targets unexpectedly as battle rages overhead. The emergence of a tunneling Trygon therefore often heralds a larger Tyranid attack, with hordes of biomorphs pouring out of the tunnel shortly after its emergence.

Winged Strain
It is speculated that the Harridan Bio-Titan is derived from a combined strain of the Gargoyle and the Winged Warrior subgroup of the Tyranid Warrior genus.
 * Harridan - The Harridan is the largest flying Tyranid biomorph the Imperium has yet encountered in it bitter war against the inter-galactic alien menace. Harridans resemble a monstrously huge Gargoyle with great wings. They are the Gargoyles' "brood-mothers" and carry their "young" into battle. Circling high above, the Harridan waits patiently before diving down over the battlefield, strafing its foes with Bio-Cannons or swooping low to rake a tank with its two massive claws, or snapping its great fanged jaws around an infantryman. This creature's fearsome armament makes the Harridan capable of attacking just about any target on the field of battle. The Magos Biologis of the Adeptus Mechanicus have noted that Harridans have been encountered in a variety of sizes. Some are huge, upwards of 30 metres in length with a sizable wingspan of 40 metres, while other, far smaller Harridans have also been encoutered that were well below the size of what would be considered a Bio-Titan and more like larger and somewhat tougher Gargoyles.

Other Bio-Titan Strains

 * Dactylis - The Dactylis Bio-Titan is speculated to be a larger genetic derivative of the Tyranid Biovore. The Dactylis hurls large Spore Mines for very long ranges. Their forelimbs are long and covered in tightly corded tendon and muscle that makes a distinctive cracking sound when used to hurl its deadly payload. When initially encountered by the forces of the Imperium, the Dactylis was noted for using the bio-weapon known as a Bile Pod. This living ammunition is a parasitic creature which feeds off the toxins emitted by the poisonous glands of the Dactylis' cranium. In recent encounters, the Dactylis has shown the Tyranids' innate ability to adapt to any combat situation or tactical need -- its cranial glands have grown a variety of spore-generating colonies that can be used to produce a number of different types of deadly ammunition that can be chosen for their particular utility against specific classes of foe.
 * Dominatrix - The Dominatrix is a specialised Bio-Titan, commanding the forces on the battlefield and providing the highest level of psychic control as exceptionally powerful -- and valuable -- synapse creatures. They are the Tyranids' largest known Bio-Titans, and it is rumoured that they sometimes carry the Norn-Queens themselves into battle on their backs. They are armed with an immensely potent Warp blast weapon, Bio-plasma emitters, and their massive chitinous claws. They also serve as synapse creatures, the Hive Mind's primary battlefield coordinators. Because of this role, the destruction of a Dominatrix can severely incapacitate a Tyranid swarm that they are responsible for directing, though the firepower required to bring down a Dominatrix is immense.
 * Norn-Queen - Tyranid Norn-Queens fill the role of the "queen" of a Hive Fleet, similar to that of a queen ant, termite, wasp or bee. As far as it is known, they are bound to a Tyranid Hive Ship and cannot leave it save under the most extreme of circumstances. They are responsible for the engineering and birthing of new Tyranids of every known bioform and they psychically communicate with the other Tyranid synapse creatures, directly transmitting the will of the Hive Mind. A Norn-Queen is always the most protected Tyranid aboard a Hive Ship, so the humans of the Imperium have been unable to garner much data about them save in the rare instances where they have been able to penetrate to the heart of a Tyranid swarm in deep space. The death of a Norn-Queen will sever the synaptic link between the Hive Mind and those Tyranids who are directly linked to that Norn-Queen, rendering them mindless, enraged beasts. The death of the Norn-Queen at Tarsis Ultra as a result of the heroic actions of Captain Uriel Ventris and the Ultramarines 4th Company caused the entire Tyranid swarm present on that world to turn on each other and become feral beasts. Norn-Queens also, to a great degree, control the evolutionary course of the Tyranid swarms. Upon arrival at a new world they intend to strip of its biomass, the Tyranids disgorge the "Alpha" swarm of biomorphs, which contain the genetic material of that particular fleet's Norn-Queen. These creatures then relay telepathic information to the Norn-Queen on the new world's environmental conditions and battlefield requirements, which spawn the second and subsequent generations of Tyranid bioforms, sometimes with tens of thousands of casualties in the collection of the data. Capture of an Alpha wave Tyranid biomorph can lead to the creation of a deadly neurotoxin which can directly affect the Norn-Queen, as was done by the Ultramarines during the invasion of Ultramar by Hive Fleet Behemoth. When a Norn-Queen is killed, the psychic backlash of its death in the Hive Mind causes nearby Tyranid Hive Ships to calve, creating more Norn-Queens within their interiors. This is an instinctual survival mechanism known as the Hydra Effect, and is the reason why even when a Hive Fleet is seemingly defeated, it can quickly form splinter fleets that in time become larger than the original.
 * Tervigon - The Tervigon is a massive creature, with a towering spined carapace that shields a swollen abdomen. Despite its massive size, the Tervigon can be deadly in close-combat, shifting its weight onto its rear legs and scything its claws back and forth in crushing arcs. The Tervigon should also not be underestimated at range -- its carapace conceals banks of cluster spines that can be fired at a considerable distance. Yet despite its fearsome weaponry, the Tervigon's true threat lies within. Each Tervigon is a living incubator beneath whose lumpen carapace dozens upon dozens of Termagants slumber in a state of hibernation. The Tervigon spawns its dormant broods at will, so that a foe engaging it will soon find itself assailed by waves of skittering Termagants. The only way to end this menace is to concentrate all firepower on the Tervigon and slay it. The resulting symbiotic backlash through the Hive Mind inevitably kills its spawn. Whilst traveling through space, Tervigons do not slumber in a dormant state. Instead, they roam the Hive Ship's cavernous innards. Should they detect intruders, it can spawn an army of frenzied Termagants to repulse the foe whilst using its potent synaptic link to awaken additional warriors.