Radiolaria

Radiolaria, referred to by some Guardians as "Vex Milk", are microscopic organisms that make up the biological component of Vex constructs, although their exact nature is unknown. Massive concentrations of radiolaria are often found on planets transformed into machine worlds.

History
It is unknown how radiolaria came into existence. They were first encountered after the Collapse when the Exodus Black crash-landed on Nessus, when the ship's AI Failsafe observed them terraforming the planetoid.

Biology
Radiolaria are microscopic organisms that are typically suspended in a briny white, luminescent fluid. They are found on planets transformed by the Vex, such as Nessus. They control the mechanical chassis of the Vex from a container usually found within their chests. On some Vex units this "brain" is located elsewhere; for example, behind the eye on Harpies or in the abdomen on Cyclopes. When radiolarian fluid comes into contact with non-Vex matter, it will attempt to turn the host into a Vex unit. Examples include Kabr, the Legionless, who drank from an Oracle and was transformed into a Vex, and Asher Mir, who lost an arm to radiolarian "infection".