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Stealthy cuttlefish use electric cloaking

Cuttlefish

Cuttlefish are renown for their tremendous camouflage capabilities – changing the color and texture of their skin to match their surroundings. They have another weapon in their hide and seek armory though – electric cloaking.

 

When a cuttlefish sees a predator, like a shark or other cuttlefish-eating fish, it freezes. The shark has eyes on the side of its head making it effectively blind straight ahead and near the front of the mouth. It relies instead on ampullae of Lorenzini which detect electrical fields.

The shark can sense a faint current emanating from the tube-like siphons on either side of the cuttlefish’s head and the gap around its mantle.

When the cuttlefish freezes it slows its ventilation, throws its arms around to cover the siphons and clamps down on its mantle, dropping its current right down.


Should the freezing trick fail, the cuttlefish’s last-ditch defense is to squirt a cloud of ink and try to escape using jet propulsion.

What makes the Cuttlefish so good at controlling its color and blending in with its surroundings? This month scientists at Harvard University and the Woods Hole Marine Biological Laboratory have helped answer that question.

It has been long known that the skin of the Cuttlefish contains chromatophores: yellow, red, and brown pigmented sacs that the Cuttlefish can expand and contract to allow their skin to act as a color filter of their surrounding light. In addition, Cuttlefish contain leucophores and iridophores that, respectively, scatter light over the entire visible spectrum and reflect light.

Under control of their nervous system, Cuttlefish can reportedly change the surface area of the pigmented sacs by as much as 500% (allowing for different combinations of pigments to be combined to a greater or lesser degree and providing different gradations in color filtration). However, that alone doesn’t explain the color repertoire of the Cuttlefish and the speed with which it can change colors.

What the scientists discovered and published for the first time is that the chromatophores also contain luminescent protein structures that allow them to actively emit light, not just reflect and filter the ambient light from their environment.

In addition, they also discovered the presence of reflectin in the chromatophores, a high-refractive-index protein that, they suggest, allows the chromatophores, when highly stretched out, to more effectively absorb light than if they contained color pigments alone. Another protein, crystallin, was also found there, adding to the understanding that chromatophores are not simply sacs of pigment as previously thought.

It is this combination of light emission and enhanced reflection/filtering abilities that provides the Cuttlefish with its impressive flexibility of appearance.

The researchers suggest that bioinspiration from the Cuttlefish could provide designs for new types of thin, flexible displays with superior color contrast and accuracy. They also note that this enhanced color contrast would provide better ability to disrupt pattern recognition as compared with pixilation camouflage technologies (such as are found in current military uniforms).

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