The Duskcoil Serpent and the Emberwick Moss

The Duskcoil Serpent

Dragon's Chasm has layers, in case you didn't know. Forest, tundra, desert, grassland, arctic. And at the very bottom, past all the parts a sensible gnome would rappel down to see, a flooded cavern that connects to the open ocean.
  No sunlight has touched that water since before Mahan was bound. Pinwheel calls it the Under-Reach. Finley calls it, and I quote, "the only place in the world I have ever been genuinely afraid to be curious in."
  The Duskcoil Serpent lives there. Slim as a boot-lace. Blind as a stone. About as harmless a predator as you will ever meet, provided you are not a cave minnow. It hunts by smell and vibration, which works fine right up until you ask how it finds mates, raises young, or avoids swimming face-first into a wall for its entire natural life.
  It doesn't manage that alone. Nothing down there does.

The Emberwick Moss

The cavern walls where Duskcoils gather are stained a faint, sullen orange. That's Emberwick Moss. It isn't a plant that wants for light. It makes its own, a slow phosphorescent bloom.
  It needs almost nothing to survive. Except one very specific thing it cannot get on its own. Nitrogen, in a cave with no soil, no rain, and nothing rotting to feed it.
  The Duskcoil provides that. Every serpent that passes over a patch of Emberwick sheds a fine mucal residue as it moves, packed with exactly the nutrients the moss can't make for itself. The moss glows brighter wherever that residue collects. Which is precisely where the serpents keep returning to feed, breed, and raise their blind, glowing young.
  The moss doesn't feed the serpent. The serpent doesn't feed the moss. And yet neither one appears anywhere in that cavern without the other close behind it.
  Finley's notes call it "an economy with no coin, no ledger, and no cheating." That's about as close to poetry as the man gets before he footnotes how much a jar of live Emberwick spores might fetch a University alchemist. I've told him that's a terrible way to talk about a family. He's told me every family is an economy if you look at it long enough. I hate that he might be right.
  Here's what I keep coming back to. The Duskcoil doesn't choose the moss. The moss doesn't choose the Duskcoil. They were simply put in the dark together, and over ten thousand generations, need did what love usually gets credit for. I don't know what to do with that. I wrote it down anyway. That's the job.