The Mist Which Fogs Mortal Eyes

"His spirit failed him, and down over his eyes a mist was shed."

Homer, The Iliad

The innermost "habitable" world. It's a sweltering, volcanic planet choked in a permanent, sulfurous fog. Monolith's Xeno-Biology Division has a small station here, studying the hyper-aggressive, silicon-based fungal life.

The fungal colonies of Achlys do not rot. They mineralize. A dead specimen hardens within hours into something indistinguishable from basalt, which made early field identification challenging, since basalt is, on Achlys, everywhere, and the early field teams were not initially looking very carefully at the rocks.

They are classified as Silicomorphic Mycotic Colonies in Monolith's taxonomy, and as "the gray stuff" in every other document produced by anyone who had actually been on the surface. The gray stuff grows. It grows fast, and it grows toward heat signatures with a directional persistence that the XBD's behavioral models classify as tropism and that anyone who has spent a night in the terminator zone would classify as something that keeps them awake.

It does not photosynthesize. It does not metabolize in any carbon-framework sense. What it does, instead, is consume. Exothermic processes. Heat differentials. The thermal gradient of a warm body against a cool surface.