The Biology of Transparency

The Biology of Transparency

The Invisible Man: Have you ever wished to be invisible? Transparency is quite common in biology, being particularly useful as camouflage in the open ocean where there is nothing to hide behind. There is an astonishing variety of transparent jellyfish, glass squid, worms and this creepy-crawly crustacean from the “twilight zone” of the deep sea seen in the image. 

How does it work? To be transparent, light must pass through without being absorbed or scattered. Most organic molecules do not absorb light in the visible range, except for the visual pigments of the eyes, which must absorb light to function. Light scattering is caused by changes in refractive index which determines how light is bent as it passes through (see http://goo.gl/7l6zFC). To be perfectly transparent, the refractive index should be the same throughout. This is clearly a challenge in biological tissues, where lipid membranes and protein/DNA rich organelles (like mitochondria or nuclei) are much denser than the surrounding cytoplasm. So transparent animals resort to a number of tricks to avoid light scattering.

See Right Through Me: One way is to become extremely flat! Since there is an exponential relationship between thickness and light absorption/scattering, a 1 cm thick tissue that is 60% transparent will achieve 95% transparency if it is only 1 mm thick. Some tissues, like the lens of our eyes, undergo drastic reduction of complexity, relying on neighboring cells to feed them. At the ultrastructural level, surfaces can be cloaked in submicroscopic bumps, smaller than half the wavelength of light that average out the differences in refractive indexes. Known as moth eye surfaces, these are responsible for the transparency of the beautiful glasswing butterfly Greta oto (see http://goo.gl/KS85mo).

I See You!: It’s hard to keep the gut transparent, unless one only eats transparent food, like the larvae of the phantom midge that sucks out clear fluids from its prey. Also, transparency can be foiled by predators that have evolved to use UV light or even polarized light to spot their prey, since underwater light is polarized particularly in the horizontal plane. A study with squid showed that they attacked plastic beads with birefringence, preferentially over beads without this optical property. Something to think about before you invest in an invisibility cloak!

GIF: This 9 cm long amphipod is nearly completely transparent. Via http://goo.gl/bL14Oy from the video below.

Video: For a short 2:41 minute video of more stunning transparent creatures, watch Deep Sea Creatures – Nature’s Microworlds – Episode 11 Preview – BBC Four

REFhttp://biology.duke.edu/johnsenlab/pdfs/pubs/transparencyreview.pdf

Musical InspirationQueen – ‘The Invisible Man’

#ScienceSunday   #ScienceEveryday  

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109 Responses to The Biology of Transparency

  1. Rich Pollett says:


    Prambug swims nicely to the Musical Inspiration 

  2. Rajini Rao says:


    Thanks, I always wondered how some creatures are completely transparent 🙂

  3. Rajini Rao says:


    Rich Pollett I recall that you posted the BBC video before. Did you mean to post a link to the “prambug” ?

  4. Rich Pollett says:


    Not really I had to use a different link to the music as it’s not available in my country. There are always alternative sources : )

  5. Rajini Rao says:


    The prambug Phronima was apparently the inspiration for the scary creature in the movie Alien  :O


    http://www.flickr.com/photos/solvinzankl/4369557020/


  6. Nice clear post.  I’ll never look at transparency in the same way again.

  7. Paris Blando says:


    What does this mean like is it a bug

  8. Rajini Rao says:


    Paris Blando , it is a crustacean, like a crab, that lives in the ocean. 

  9. steel Mack says:


    Wow amazing.. that’s for sharing..

  10. Paris Blando says:


    Rajini Rao so it is not a bug like

  11. Jaz Emminger says:


    Wow….your posts are always so amazing! How is it that some post with a cat gif gets “what’s hot” and this doesn’t?

  12. Sam Sharma says:


    Rajini Rao just amazing , what a creature.

  13. Jim Tipping says:


    Neat-O! Thanks for the enlightenment. 

  14. Rajini Rao says:


    Jaz Emminger I’d better start posting cat gifs then 🙂

  15. James Brine says:


    My favorite example is the glass catfish, remained hidden to many predatory fish in one of my tanks for several years before it died due to a nitrogen spike from a dead molly, it is greatly missed.

  16. Rajini Rao says:


    James Brine that’s pretty neat that the glass catfish avoided predators even in the confines of a tank! 


    Here’s a nice image of transparent catfish: http://www.practicalfishkeeping.co.uk/custom/images/large/amyc0eezg.png 

  17. James Brine says:


    Rajini Rao it always amazed me that the larger fish like oscars were completely oblivious to it and allowed it to continue being a surface feeder. Having plenty of places to hide helped of course. 🙂


  18. great post, awesome information, and very interesting topic.

  19. Rozni Yusof says:


    I always look forward to your posts, miss/ madam. Not very frequent but always worth the wait. 🙂

  20. Rajini Rao says:


    Rozni Yusof, thank you! I make sure that I have time set aside to respond to comments, and that’s not very often. Love the feedback. 


  21. Fascinating information Rajini Rao I learn so many new things from your posts.Thank you for sharing!

  22. Rajini Rao says:


    Same here, Siromi Samarasinghe !

  23. Rajini Rao says:


    Siromi Samarasinghe , a very short one. Visiting parents in B’lore followed by a few days in New Delhi for a conference. Anjana is with me too. So glad to be home.


  24. Very interesting. Many thanks Rajini Rao. You mentioned thickness that half the wave length of light. My mind blew off!!

  25. Rajini Rao says:


    Indeed, R Prakash Prakash . It has to be viewed with an electron microscope since it is below the resolution of a light microscope! 


  26. Thank you for the time and energy you put into this interesting post, Rajini Rao

  27. Rajini Rao says:


    My pleasure, Deborah L Gabriel . I was jet lagged from traveling and putting this post together turned out to be the perfect way to keep myself busy 🙂 

  28. Shar Banning says:


    Wonderful Rajini Rao! Thanks for tagging me in Annelouise Verboon. 😀

  29. Patel Rajesh says:


    Nice good morning to all

  30. Marta Rauch says:


    Fascinating topic. Thank you, Rajini Rao!

  31. John Deere says:


    A deep sea creature using water instead of a skeleton. 

  32. Alison Bell says:


    Great post, that is awesome.


  33. Transparency is not only for biological works….it’s also for each movement of life…without transparency we cant see the truth behind our life.

  34. Mary T says:


    Fascinating post and beautiful video Rajini Rao :-).

  35. Adit Morey says:


    These creatures are already equipped by nature with such a great technology.

  36. Rajini Rao says:


    Adit Morey good point. We should try to replicate their nanotech “cloaking device”.

  37. Linda Redman says:


    I learned something new and it was very interesting.

  38. Rajini Rao says:


    Anupama Sharda , I’m glad that you enjoyed it! I have indeed shared it to Science on Google+ community (it’s in the Life section). Is that the one you meant?


  39. Rajini Rao it is very nice yah…

  40. Rama Drama says:


    I want to be invisible but visible to the ones I love Rajini Rao 🙂 Not much fun in life when you don’t exist…very creepy but wonderful gif at same time :)..Love the musical inspiration…when art inspires science or vice versa, it is pure magic 🙂

  41. Rajini Rao says:


    Glad you approved of my excuse to post Queen, Rama Drama ! Definitely, the invisibility should be reversible. I’m thinking of the time when nosy relatives come to call….

  42. Rama Drama says:


    Rajini Rao Thats one of the reasons I love G+ to FB..where you can’t say anything about nosy relatives 😉


  43. cool but that picture is kind of freaking me out 


  44. Wonderful posting, thanks for that.


  45. Amazing wonders of nature!


  46. This is a wonderful post, Rajini Rao 🙂


    Happy New Year, as well.

  47. Rajini Rao says:


    Thanks, hope you have a wonderful 2014 Daniel Mihai Popescu 🙂

  48. jeetu kumar says:


    so nice and .happy new years


  49. I’ve been told I can’t ask for your friendships unless I know you! If y’all want to be are more correctly make Friends y’all will have to move first! Thanks again for your support David R Cape go and Love All 54David!


  50. Rajini Rao you take me to my childhood once again: playing with transparent shrimps in tidepools!

  51. Rajini Rao says:


    Aren’t transparent creatures beautiful?! I’m delighted to bring back those memories, nomad dimitri 🙂


  52. Rajini Rao i have swam with indonesian jellyfish for hours, they were as big as me!

  53. Gen A says:


    BTW that looks really creepy

  54. Rajini Rao says:


    Isn’t it?! Have you seen my last post on molting tarantula? 😉

  55. Rajini Rao says:


    Well then, take a look, unless you are scared of spiders 🙂

  56. M.A. N. says:


    Now it needs swimming lessons, at the moment it won’t win any titles! Extreme high speed appears transparent too!


  57. 気持ち悪い、エイリアンか?

  58. 张鹏飞 says:


    Really awesome!

  59. Micki Mick says:


    This is so beautiful

  60. Luna Ephraim says:


    Looks like a bubble.


  61. Very amazing creature


  62. What creature is that? However that was cute


  63. この世のものとは思えない、生物ですね、


    山本溶接

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