Radiolaria

Radiolaria, referred to by some Guardians as "Vex Milk", is the liquid biological component of Vex constructs, although its exact nature is unknown. Massive concentrations of Radiolaria are often found on planets transformed into machine worlds.

History
It is unknown how Radilaria came into existence however Radiolaria was first encountered after the Collapse when the Exodus Black crashed landed on Nessus and their Failsafe saw them terraform the centaur.

Biology
Radiolaria is a white electric being found on Vexised planets such as Nessus and is what powers and controls the Vex within their chests however some Vex have this "brain" located elsewhere. Such as Harpies who have is located behind their eye or Cyclopes who have it located on their abdomen. If Radiolaria comes into contact with anything, it will attempt to turn it into a Vex regardless of what it is. An example was Kabr, the Legionless who drank of an Oracle and transformed into a Vex.