The Daemonculaba was the name given to the individuals used in the attempt to create new Chaos Space Marines from the mutated womb of a Human female, making use of the uncorrupted gene-seed stolen from the Imperial Fists' repository on the world of Hydra Cordatus.
It was a project undertaken by the Iron Warriors Traitor Legion, and overseen by the Warsmith Honsou. It took place deep within the dungeons of Khalan-Ghol, Honsou's fortress on the Daemon World of Medrengard.
The creation of the Daemonculaba began with the rounding up of Human females present on Medrengard as slaves. Once corralled, they were shackled naked within iron cages and force-fed nutrients which caused their bodies to widen and bloat to grotesque proportions.
Next, the Hereteks known as Savage Morticians utilised surgical and chemical techniques as well as the sorcery of Chaos to radically alter the slaves' internal morphology and embed within their wombs the stolen Imperial Fists gene-seed.
Once this "birthing-womb" was readied, an adolescent Human male drawn from Medrengard's slave population was sealed within through the use of a surgical procedure that was essentially a "reverse C-section."
Days later, the new Astartes candidate was reborn from the womb of the Daemonculaba lacking any skin. Provided they had not died from metabolic shock during the process, the candidate was inspected to see if he was physically worthy to be an Astartes.
If he was not because his body had horribly mutated during the transformation process, he was literally flushed through the sewers of Khalan-Ghol to die in the barren wastelands of Medrengard surrounding the fortress.
If the candidate passed the inspection, a new skin would be cross-stitched onto his body and his life as a Chaos Space Marine of the Iron Warriors would begin.
The skin was harvested from the flayed bodies of Human slaves whose flesh had first been painfully stretched to the necessary proportions to fit an Astartes before they were flayed alive.
The system could also use genetic material extracted from the corpses of Iron Warriors Heretic Astartes, which would then be implanted within the Daemonculaba and fed to the maturing Astartes "child" rapidly maturing within.
As for the Daemonculaba themselves, if they happened to survive the birthing process, the nightmarish cycle would begin anew only solar days later until death finally brought release.
Varro Tigurius of the Ultramarines had experienced visions of the Daemonculaba, in the form of nightmares brought to him by his potent psychic presence in the Warp. This prompted the Ultramarines Chapter Master, Marneus Calgar, to sentence the recently dishonoured Ultramarines, Uriel Ventris and Pasanius Lysane, to carry out a Death Oath which required them to seek out and destroy such abominations within the Eye of Terror.
With the help of the Unfleshed, Uriel and Pasanius ultimately succeeded in this mission. The Warsmith Honsou swore to obtain vengeance against Ventris and the Ultramarines for the destruction of his plans to build a new army of Iron Warriors Heretic Astartes that would allow him to rule all of Medrengard.
- Dead Sky, Black Sun (Novel) by Graham McNeill