|Previous Edition Warning: This article discusses a topic from a previous edition of Warhammer 40,000.|
Its canonicity is in question but was once considered canon.
Bonded Exoskeletons come from aging, and the older an organism the tougher its chitin. Various layers of bone, muscle and cartilage grow over various vital spots, forming a sleek cover over the entire body. This makes creatures extremely tough and difficult to kill.