The Hulun are a primitive race fro the planet Sacrosa. If no aluminide prey is avalable, They inhale sulfur and bromine fluorides and exhale carbon tetrafluoride and silicon tetrafluoride. They must also eat sand containing aluminum, and silicon/carbon. A diet of either of the latter will produce the associated gas.

Hulun are worm-like, and have an inner structure consisting of a hardened skin, soft flesh, an insulating layer of gallium, and finally a stomach containing antimony pentafluoride, which it sprays onto meals (or mineral sand) for pre-digestion. They have a central hole in their face protected by a clam-like shell, with various sensory organs in an area around it.

The hulun exist in small tribes/herds, with specialization for proctecting the area, to caring for the breeding site. hulun have passed many psycological tests for inteligence, and are thought to exist on the brink of sentience. Hulun are also known to farm Serenari by feeding it, and then pasteurising the parasitic nature of the flesh with acid for digestion.