The Black Carapace, also known as the Interface, is the last and one of the most important of all the 19 gene-seed organ implants a Space Marine Neophyte will receive as he is transformed from a normal, adolescent human male into a superhuman Astartes. This neuroreactive, black organic fibrous material is implanted directly under the skin of the Neophyte's torso. Points are then cut through the Carapace by an Apothecary using surgical tools that allow a Space Marine to directly interface his central nervous system with his Power Armour's cybernetic systems. After a few hours, the material hardens and invasive synthetic fiber bundles that will serve as connection points for neurons grow inward and interlink with the newborn Astartes' central nervous system. Note that a Space Marine needs the Black Carapace to use his Power Armour to its maximum capabilities, but the armour itself does not need this implant in order to function. The Sisters of Battle, for example, as well as some Inquisitors, also wear Power Armour. However, since their central nervous systems are not linked directly to their armour's Machine Spirit as a Space Marine would be, their Power Armour is markedly less efficient at providing protection or allowing them to maneuver in combat than that of an Astartes.
- Codex: Space Marines (5th Edition)