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Deep Sea Squid Uses Optical Fibers To Create An Invisibility Cloak

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Benjamin Taub

author

Benjamin Taub

Freelance Writer

Benjamin holds a Master's degree in anthropology from University College London and has worked in the fields of neuroscience research and mental health treatment.

Freelance Writer

Glass squid
A glass squid. Photograph by Darren Stevens of New Zealand, International Polar Year and the Census of Antarctic Marine Life. Wikipedia/ CC BY 3.0

With their color-changing, luminous ink-squirting, whale-shredding abilities, it’s hardly as if the many varieties of squid found in the world’s oceans were ever lacking in awesomeness. However, if you need yet another reason to make the squiggly cephalopods your favorite animal, then you should be aware that there’s a deep sea squid that has its own invisibility cloak.

Known as the glass squid, this wobbly torpedo is fully transparent apart from its eyes, which stick out like magic eight balls. Even at the extreme depths at which the animal lives, this can make it conspicuous to predators, especially those that attack from below. When looking upwards, they may be able to detect the squid’s eyes blocking out the faint light that penetrates from the surface.

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To get around this, the squid’s eyes are equipped with small fiber-like organs called photophores, which emit light downwards so that the animal can’t be seen from below. While this is pretty smart, it doesn’t explain how the glass squid protects itself from predators viewing it from other angles.

A new study in the Journal of the Royal Society Interface details the work of a team of researchers who examined these photophores up close, describing them as “incomplete, asymmetric ellipses that will tend to emit light from their sides and their ends.” In other words, they are “leaky”, allowing light to escape sideways as well as downwards – something which initially surprised the study authors, as evolution tends to drive most organisms towards perfection rather than imperfection.

According to the researchers, achieving such perfection would not be particularly difficult, given that only a few “minor geometric adjustments” are required in order for these fibers to “guide light to their ends with efficiency approaching 100 percent.”

Glass squid eyes, complete with photopheres. Amanda L. Holt, Alison M. Sweeney/Journal of the Royal Society Interface

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To investigate how this defect affects the squids’ visibility to predators, the study authors recreated their photophores and placed them in a tank of water with similar light conditions to their deep sea habitat. In doing so, they found that this allowed the squids’ eyes to emit light in all directions that matched the varying radiance of the natural light present in their environment.

For instance, they discovered that light traveling downwards in the deep sea is between 25 and 500 times brighter than light traveling vertically. As such, it is vital that the glass squid is able to reproduce this variation in radiance as it reflects light in different directions.

Based on this finding, the researchers explain that the fibers actually “evolved to be leaky,” as this allows for “dynamic matching of radiance from all angles and at all positions” within a deep sea habitat, essentially making the squid invisible.

So, it looks like you now have a new favorite animal.


ARTICLE POSTED IN

natureNature
  • tag
  • prey,

  • bioluminescence,

  • deep sea,

  • squid,

  • predator,

  • glass squid,

  • photopheres

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