Guhnuh

The guhnuh has fleshy fins located farther down on its body than its ancestor's fins. This change in position allows the fins to support its weight, letting it "sit" in place. This conserves energy compared to swimming in place, making it a useful adaptation when there is little food. Furthermore, the guhnuh barely moves unless it detects food. Its eyes are slightly bigger than its ancestor's, improving its vision in the low light conditions of its habitat. The guhnuh's eyes are always looking upward, as that is where its food comes from. A mutation caused its single eye to duplicate, but the two eyes don't have separate eye sockets. They are joined by a shared "corneal strip" and use the same optic nerve. (The corneal strip is toughened in comparison to the functional corneas.) Its single optic nerve serves two eyes by rapidly alternating which eye it receives signals from. The optic nerve is more developed on the left side, so it starts receiving signals from the left. It then switches to receiving signals to the right eye. The whole alternating process occurs within milliseconds. Despite the delay, the guhnuh's brain ties the two signals into one simultaneous view. Timing "trickery" by its brain makes it unaware of right-eye delays relative to its left eye. In lab conditions, flashing the image of a black square to the left eye for a millisecond, making the black square image blank and then flashing the image of a light grey square to the right eye for a millisecond makes the guhnuh perceive the square it saw as dark grey, since its brain ties what either eye sees within a range of milliseconds into one image.

Diagram of guhnuh eye from a top-down perspective. Dark blue: Lens, Medium blue, "Corneal Strip", Light blue: Cornea, Green: Retina, Purple: Optic Nerve. While guhnuhs don't have very complicated eyes, this diagram is still simplified. Guhnuhs have two tooth-like rasps in their mouth, which they use to scrape off food. This is useful for eating every scrap of meat on a sunken carcass or sustaining themselves on the skin flora of delving lyngbakrs. Their mouths are elongated and capable of some sideways articulation, which is useful for eating bits of flesh in hard-to-reach spots. Guhnuhs can still swim, but only poorly. They swim only when they detect food. Once at the feeding site, they prefer to move on their fins. (Perhaps a predator of the guhnuh can exploit the way its brain works while simultaneously making itself highly visible to its conspecifics. It would make its entire body flash black and then light grey very rapidly to blend in with a dark grey background, making it appear to match the background for the guhnuh and look like a strobe light to conspecifics.)