prettyokayray said:[re: cuttlefish masquerading as crabs] aren't cuttlefish also blind??
They’re colorblind, but not totally blind. Yet they’re still able to match the colors of the area around them, not just the contrast! It’s all because cuttlefish skin is super cool.
Basically, cuttlefish skin is covered in chromatophores - little organs that have muscular control and contain pigmented sacs. Each is attached to it’s own nerve, which mean they can be controlled independently. As these dilate or contract, different patterns display across the skin. Chromatophores contain some basic colors - generally only yellow, brown, and/or red. What’s more, the skin itself contains light sensitive pigments that process information about the animal’s immediate surroundings - but still, they’re matching to information about degrees of contrast, not color.
(First image - individuals chromatophores at a high resolution. Second image - a diagram of the inside of a chromatophore. From Nature).
So where does the ability to accurately change color come from? It turns out there are two different other types of cells in cuttlefish skin that allow them to - entirely passively - match and mimic the colors in their environments. These are called iridiophores and leucophores.
Iridiophores are basically stacks of thing cells that reflect light back at different wavelengths depending on the angle that they’re observed at. When viewed from above they look blue, but appear red from a more oblique angle. Since cuttlefish can control the texture of their skin as well as the chromatophores in it, a correct positioning can allow these cells to contribute to the visual appearance of the animal.
Leucophores are another type of reflector cell that is specific only to cuttlefish and octopus, and they have two jobs. Leucophores both scatter full-spectrum light in a way that makes them appear white (this is a similar reason to why polar bear fur appears white) and reflect back whatever color of light they encounter. They don’t change depending on the viewing angle, but are thought to support color matching by reflecting ambient light and by helping to break up the cuttlefish’s outline.