Friendly-looking, big-eyed, and found in shoals like fish — the Morivarid pass for harmless right up until they're on you. They are the cleaners of the murk, and what they clean is soft tissue: eyeballs first, then the tongue, then the flesh off the bone. You hear them coming, if you hear them at all, as a sound like a wet cough.

Syncarid don't announce themselves - you feel the pull before you understand what's pulling, and what they're consuming is not your mind but the programme running inside it, the accumulated decisions and self-preservation instincts that make you a person rather than a body. At zero murk, you walk toward them; this does not feel like a loss of control. It feels like a very good idea.

Morivarids are the size of a small bird, clean the murk, and look something like a friendly fish — large eyes, smooth form, the kind of thing you are already leaning toward when the first one takes your tongue. They come in threes: one to distract, one to feed, one to watch. Killing the first makes the other two significantly less cautious, which is the worst possible trade.

Dyapnids are the size of a spaniel barker, move in coordinated packs, and will wait at the treeline for days before deciding to flush a position. Their mandibles crack bone.