Living paint

Remember this little octopus from the post on 28 January 2013?  (We think it's a juvenile Red Octopus, Octopus rubescens.)

 

We decided to take a few pictures and video of it through a microscope.  Watching an octopus under a microscope is an unforgettable experience.  Their skin is alive with color.  It's as if you're watching living paint.  

Look for the thousands of small spots of color scattered across the skin.

 

Close-ups reveal the dominant colors: yellows, oranges, reds, and browns.

 

 

Octopus color patterns are quite complex.  They involve different types of organs and cells.

Chromatophores are responsible for most of the colors you see above.  Visualize a sac-like structure that contains pigments.  Muscles radiate away from the sac.  When the muscles contract, the sac expands and the color broadens.  When the muscles relax, the sac shrinks as does the color.  The muscles are controlled by nerves which receive signals from the brain.

To illustrate size change in chromatophores, here are two before and after images taken in quick succession — the first with the chromatophores reduced and the second with them expanded.  Pick any spot and trace it from the first photo to the second to see the change.  Note that each chromatophore is controlled independently, so some of them expand more than others.

 

 

Another type of cell involved in octopus color patterns is called an iridophore.  These are stacks of platelets alternating with cytoplasm that are reflective.  They are responsible for green, blue, violet, and silver colors.  I'm not an expert, but I think I found iridophores near the eyes and suckers of this octopus.  Look for the sparkling, iridescent patches in the pictures below.

 

 

 

Leucophores are responsible for white spots or patches in octopus skin.  If you go back to the first microscope photo, you can see a few white splotches here and there.

Although I'm trying to highlight the amazing skin of an octopus with these photographs, there's nothing like seeing it in motion.  So here are two short video clips that provide a glimpse of chromatophores in action.  Watch as the octopus darkens to brick red within seconds.  The videos are shown in real-time (not sped up), and are best viewed at the smaller size for now.

 

 

"The beautiful play of colour and pattern in the skin of a living cephalopod appears almost magical.  The extraordinary patterns in the skin and the speed with which they change are due mainly to tens or hundreds of thousands of chromatophore organs under neuromuscular control directly from the brain.  Cephalopod chromatophores are thus unique in the animal kingdom, and in many shallow-water forms nearly all behaviours are inextricably bound up with chromatophore activity.  Feeding, avoiding predators, mating and communication all involve the chromatophores..." 
(In Cephalopod Behaviour by Hanlon and Messenger, 1996)