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Octopuses and other cephalopods can 'see' with their skin

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Octopuses and their tentacled brethren are fascinating, and even a little scary. In addition to their uniquely alien intelligence, cephalopods are known to change color based on their surroundings. That ability is thought to rely mainly on eyesight, as the creatures can visually detect basic changes in the environment and camouflage themselves in order to hide from predators. However, new research shows that pigment proteins found in eyes are also present in cephalopod skin, allowing them to detect different kinds of light without input from the brain.

The research, published in the Journal of Experimental Biology, investigates how cell structures known as chromatophores interact with light, and is an extension of research on octopuses that was conducted in the 1960s. Chromatophores contain pigment and control color expression in the skin — melanocytes in humans function the same way — but in cephalopods they also feature rings of muscle that allow them to expand, changing their color.

Researchers were able to prove that chromatophores respond directly to light by taking biopsies of octopus and squid skin and exposing it to different wavelengths of light. The chromatophores in the skin samples expanded the most when exposed to blue light — the same kind of light that opsins, or the proteins found in eyes that detect pigment, respond to the best. The team then tested the skin for the presence of opsin genes, and discovered that the sensory neurons in the skin produce the opsins needed for light detection.

Cephalopods are believed to be colorblind

The findings are significant because cephalopods are believed to be colorblind, so their ability to mimic their surroundings has confounded observers for years. Research published in the 1970s showed that while octopuses can distinguish between light and dark colors, they were unable to recognize different hues. While cephalopods aren't alone in their having light-detecting opsin in their skin — other animals like the Moorish gecko are capable of much the same — this research gives a clearer picture of how the octopus evolved one of its more fascinating behaviors.