The Mucranoid, also called the Weaver, is the 16th of the 19 gene-seed organs implanted within an adolescent Space Marine Neophyte to create a new Astartes. This organ is implanted within the central nervous system and responds to specific chemical stimuli in the environment, causing the Space Marine to secrete a waxy protein substance similar to mucus through his pores that seals his skin. The gland's operations must first be activated by an external chemical treatment, usually self-administered, before it will activate. Space Marines are cocooned in this way before they enter suspended animation, and the process can even protect them from the harshness of the vacuum and other extremes of temperature, particularly deeply frigid environments.
- Codex: Space Marines (5th Edition)