The Carnifex or Carnifex Primus (Carnifex voracio, Carnifex vorantii, Carnifex ululare, Carnifex arbylis, and the Carnifex bilius) is a monstrous creature that essentially acts as an organic main battle tank for the Tyranid Hive Fleets. It is armed with the most advanced Tyranid Bio-Weapons and is used primarily as a shock trooper to carry out starship boarding actions, frontal shock assaults on entrenched positions and for besieging fortified locations or enemy armour formations. As Tyranids are constantly evolving their forces, many different species of the Carnifex exist. However, all Carnifex share some common characteristics: they are very large creatures, standing significantly larger than a man; they have a thick carapace, which provides excellent protection from damage, and they frequently use some of the bio-weaponry utilized by the Tyranids. They are comparable to the Space Marine Dreadnought and Ork Killa-Kan in tactical use. A Carnifex is a living engine of destruction that is impervious to small arms fire. Any Carnifex can be mutated to possess Thornback Armour, a Barbed Strangler, Spore Cysts, a Venom Cannon, or to project burning Bio-Plasma.
The standard Carnifex bioform is classified by the Ordo Xenos as the Carnifex voracio. However, the forces of the Imperium have encountered four other major sub-species of Carnifex: the Carnifex vorantii, the Carnifex ululare, the Carnifex bilius, and the Carnifex arbylis. These are more commonly known, respectively, as the:
- Thornback (Carnifex vorantii): The Thornback Carnifex bears genetic enhancements that resemble large spikes or thorns and are used to push through an enemy's lines.
- Screamer-Killer (Carnifex ululare): The Screamer-Killer was the first type of Carnifex encountered by the military forces of the Imperium. It is known for emitting a piercing shriek before shooting Bio-Plasma.
- Bile-Beast (Carnifex bilius): The Bile Beast spews acidic fluids onto its foes before attacking in close combat using its huge crab-like claws.
- Stone-Crusher (Carnifex arbylis): The Stone-Crusher is a variant of the Carnifex intended for use as a siege unit against fortifed targets. It is armed with huge wrecking claws, capable of tearing down the thickest of fortifications, a heavier version of a scything tail, and battering rams; used for crashing into enemy ranks, and fortresses. Other sightings of this creature have been seen with a large wrecking-ball looking symbiont.
- Codex: Tyranids (5th Edition)
- Imperial Armour Apocalypse Second Edition, p. 74