Isolated broods of this Tyranid creature are typified by a blue-indigo coloration. Such beasts have been encountered not only on numerous Space Hulks, notably the Sin of Damnation, but also upon the moons of Ymgarl, once thought home to a tentacle-mawed variation of the xenoform. This strain is possibly specifically nomadic; bio-engineered purely to infect new hosts. Some of these pods are filled with microbial life. These hostile micro-organisms immediately begin to change the planet's atmosphere, oceans, soil, flora, and fauna. Complex organic molecules are broken down and recreated in formats that are best suited for absorption by the swarm. Other spores bear more complex Tyranid creatures. By spreading their genetic curse in secrecy, these creatures multiply the threat they pose in the manner of a virus. Even a single Purestrain Genestealer, borne across the stars by an unwitting pilot who lands upon a fertile planet, can spawn enough tainted progeny to take that world over from the bottom up. Such potential disasters are seeded across the Imperium in great measure.

The mentality of the Tyranid approach to warfare can be described with the phrase "quantity has a quality all its own." From the "lowly" Ripper, to the deadly Hive Tyrant and beyond, the signature of the Tyranid species is that they overwhelm their foes with sheer numbers, reproducing massive numbers of highly virulent organisms in record time from the biochemical soup that they derive from the biospheres of the worlds they consume. Situated within this tangled web are specialised "synapse creatures" whose slightly more advanced brains function as psychic routers, buses, and hubs, co-ordinating and policing the riotous cacophony of the collective brain power of a mass organism that is sometimes larger than most planets. Tyrant Guard - The Tyrant Guards are a special species of Tyranid spawned in small broods for the sole purpose of defending the Hive Tyrant. They are large, tough, and difficult to harm, and it is nearly impossible to surpass their defense. Tyrant Guard are completely blind, utterly controlled by the synapse creatures they protect. On occasion Carnifex also benefit from the Tyrant Guard's protection. Tyrant Guard are believed by some Adeptus Mechanicus Magi to contain the DNA of the defeated Space Marine Chapters, but the Imperium considers this blasphemy and denies its very likely possibility. Their secondary limbs are typically shaped like gnarled hands, allowing them to manipulate objects, climb and even operate simple devices such as touch-panels. The number of digits differs depending on the parent organism. A Genestealer hybrid of four or more generations of consistent Human parentage would pass for a baseline Human on cursory inspection, although a closer look would reveal bluish skin, sharp, pointed teeth and unsettling behaviors.

Hive Fleet Moloch

Tyranids appear in a multitude of genera, and all have an extremely rapid rate of evolution directed by the Hive Mind, adapting to threats in direct response to their presence. Tyranid matter is constantly reabsorbed into biomass reclamation pools to create new species and adapt existing ones to suit the Hive Mind's immediate purpose. Taking a fully upright stance, the Third Generation Hybrid is reminiscent of many mutants in Imperial society. Their foul features go unnoticed in the underhives of many Imperial worlds. Yet the Tyranids crossed this expanse nonetheless, moving through the empty darkness for countless millennia to reach the rim of the galaxy. All these creatures are born to service the ship, and the ship in turn exists only to service the needs of the Hive Fleet. Whereas other armies like those of the Imperium and the T'au fight for conquest or self-defence, and the forces of Chaos and the Ork tribes battle merely for the chance to wreak violence and havoc, the Tyranid hive fleets are driven by the will of the Hive Mind, which itself is motivated by the most ineradicable instinct inherent to all lifeforms -- reproduction, and through reproduction and the acquisition of new genetic traits, evolution to a better adapted form. As this happens, many of the Capillary Towers are also broken down so that their biomass may be reabsorbed. Finally, the planet's atmosphere, and then the last few massive Capillary Towers, are absorbed into the Hive Ships.

These layers provide a considerable degree of protection; combined with their naturally tough physique it is possible for a Genestealer to charge headlong through a volley of Lasgun fire and survive. As with other Tyranid organisms, they typically have an open circulatory system with haemolymph flooding the intercellular spaces. This system is host to unnumbered phage cells, believed by the Magos Biologis of the New Hallefuss research facility to be digestive systems. Just as it seemed the defences of the Segmentum Solar and perhaps Terra itself would be tested, the Tyranids were distracted by being deflected into the star system of the powerful Ork Empire of Octarius in the Octarius Sector of the Segmentum Ultima. The Genestealer DNA will be incorporated into the host's germ cells and so any child that results from this union will be a Genestealer hybrid, which now has the complete loyalty of its parents through a psychic bond.The mutable, inconstant psychic energy of Chaos provides none of this vital sustenance. With every passing season, more planets and systems are swallowed up by the roiling tide of empyric madness, denying the Tyranids the precious biomass that sustains them.