Cuttlefish colors

Octopuses abd other cephalopods can make patterns on their skin to camouflage against background or to communicate with fish or other cephalopods.

The entire body is a pixeled screen on which patterns are played. Neurons reach from the brain out into the skin where they control pixel-like sacs of color.A typical cephalopod may control tens of millions of colord pixels, which is comparable to the resolution of a cell phone camera. A cuttlefish senses or decides something and its color pattern changes in an instant.

Below the outer layer of skin are the chromatophores, the most important of the color control devices. A chromatophore consists of a sac of colored pigment [less than 1 mm in diameter] surrounded by dozens of muscles that can pull the sac into different shapes. Each chromatophore contains just one color. Usually, chromatophores come in three color types, which vary from species to species. In the giant cuttlefish, the sacs are red, yellow, and dark brown. Chromatophore colors can be combined, but there is no way to produce blue or green from the chromatophores of the giant cuttlefish. These colors are produced, however, by reflecting cells (iridophores) in the skin layer beneath the chromatophores. Incoming light is filtered and partially reflected by stacks of semi-transparent plates. The light that shines back can be different in color from the light that came in. Iridophores are not connected directly to the brain, and yet the animal seems able to create blues and greens with them at will. Below the iridophores is a layer of leucophores, another kind of reflecting cells. They can reflect (or not) whatever color impinges on them. Part of the input to the leucophores and iridophores is ambient light, and part comes from the chromatophores. [Nature article]

Cephalopods use color patterns to camouflage themselves against whatever background they are resting. Their skin contains light sensors, millions of tiny eyes that help enable this ability. But a mystery is that the eyes and skin of cephalopods contain only one kind of color receptor. Human eyes, by contrast, have three, which are thought to enable our color vision. We don’t know how cephalopods perceive color, either with their eyes or with their skin. But obviously they do, because when camouflaging, skin patterns are color-matched to the background.

Octopus individuals do not always wish to camouflage themselves. Body color patterns are also used to communicate with other octopuses, to warn or to invite or to express other messages that human scientists have yet to decode. An octopus might present one view to another octopus on its left, while camouflaging itself as seen from the right.

Not only color but also texture of the skin can be changed at will. The skin can be smooth or bumpy or lined with ridges. The gross form of the body is also under exquisite control. When showing aggression, male cuttlefish will often flatten their fourth arms into shapes like broad blades. Another aggressive gesture is to hold the first pair of arms vertically like horns. Some cuttlefish make the arms elegantly wavy, while others shape their arms into fiddleheads, hooks, or clubs. In the most elaborate cases, cuttlefish will arrange their arms into four different levels. The first arms are tall and straight; the second arms horn-like at a lower level; The third and fourth pair of arms are flattened, and made to appear as massive as possible.

Some individuals have distinctive styles of color change. I’ve occasionally encountered cuttlefish who produce colors the others have not thought of, or patterns with particular brilliance. One of these, I named ‘Matisse’. He was a friendly cuttlefish I visited over the course of several days…He would be hovering without fuss in some mixture of reds and whites and would suddenly explode into bright, canary yellow. This flood covered his entire body, with no other marks visible…One moment he would be dark red with veins and stripes, and in less than a second he looked like a sun. The flare would then fade more slowly, with oranges darkening among yellow patches. In ten seconds or so, he was dark red…

Kandinsky had fixed habits and a home base. He produced all the colors of his peers, but in a more extravagant way. For about a week, I would visit his home in the late afternoon, seeking to photograph him. He would have arms going everywhere like a collection of ceremonial lances…On his skin, Kandinsky favored flaring mixtures of red and orange, including a kind of pale orange-green. He often combined these colors with a “passing cloud” display, in which waves of dark shapes flowed over the skin. Tear-like patterns moved down his inner arms.

The above is excerpted and edited from Other Minds by Peter Godfrey-Smith

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