Bellix
The Bellix is a benign soil microbe, living in the silty bottoms of its habitats. It "eats" simple hydrogen compounds, such as methane, ammonia and hydrogen gas, and "breathes" from all the kinds of metals its ancestor can use. It cannot, however, breathe from copper, and is in fact poisoned by it.
It co-occurs with other silt-dwelling microbes with no need for oxygen. Where the concentrations of metals, hydrogen compounds, and low oxygen are just right, it can form barely-visible light bluish specks in the silt 0.5 cm-2 cm down, forming a distinct layer.
Physiology
As a microbe from an ancient lineage, it has a strange mixture of needs, strengths, and weaknesses. It has no need for oxygen, although it can tolerate low oxygen levels. Sustained exposure to high oxygen levels will, depending on the exact levels and time span, slow its growth, halt its growth entirely, or kill it. In the LadyM Twilight Floor, it is rare above the oxygen minimum zone, and common below it.
The Bellix is one of the most radiation-resistant microbes at time of evolution, and can withstand low levels of UV light indefinitely (although the ability is useless in its present biome). However, very high UV exposure shall kill it quickly. Should a Bellix ever get stuck on a large migratory organism and carried up to the waters' surface in the daytime, it will die in roughly ten to thirty minutes, depending on sunniness and latitude.
The Bellix is sensitive to the oligodynamic effect, although copper is its most notable and severe "weakness". Like many microbes, it is also killed by high concentrations of chlorine. Unlike the Skarlixids genus group, it cannot form oval cysts to withstand harsh conditions.
Infection
Much like the normally-harmless soil bacterium tetanus, the Bellix can also be a life-threatening condition.
Rarely, silt containing Bellixes can enter the open wounds of Geletaventrians. They feed upon hydrogen compounds floating within the blood, in ruptured tissue, or water going past the wound, and "breathe" using metal compounds in the blood or tissue. They may multiply within the wound, provided there's not enough oxygen, and overwhelm the host. However, it is not so much the Bellix's ability to infect hosts that's the problem, so much as the host's lack of blood defenses.