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One of the hallmark moves of  octopuses and their cephalopod relatives is that  they can squirt ink when they feel threatened.  Typically,  we think of this ink as an underwater  smokescreen. And it can be used that way.     But cephalopods have had the ability to   ink for at least 300 million years, and in that  time, they’ve gotten pretty creative with it.    We’re talking toxic clouds—mucus-y   decoys!—and even a dazzling display of underwater  pyrotechnics.

Trust me: cephalopod ink is so much   cooler than you’ve ever realized.      It seems like inking evolved primarily   as a way of avoiding getting eaten.    Early cephalopods all had external, hard shells to  protect their soft bodies, but as time progressed,   they lost or internalized those shells.     And researchers believe that as that happened,  the ink sac emerged as another form of defense.  This theory tracks,   seeing as nautiloids — the only cephalopods around today that have a protective shell — can’t ink.  Plus, anyone who’s seen a big ole cloud of ink in the water  knows it works super well as a smokescreen.    But not all cephalopod inks are the same.   You see, what we call “ink” is a mixture made by two separate glands: the ink gland and the funnel organ.  The ink gland is responsible for the actual color you see — that black-brown hue, courtesy of the pigment melanin.     This gland is an off-shoot of   the cephalopods digestive tract. So, you could say  these creatures are all technically pooping ink.     Meanwhile, the funnel organ is   located in the siphon — the tube-like organ that  cephalopods use to expel water, waste, and ink.     It makes mucus which combines with the ink gland’s   pigments before they’re released into the water.    While the melanin in cephalopod ink hasn’t  changed in millions of years, there are lots   of other components that do vary depending  on species, like toxins and amino acids.  And these can give the ink different properties. For instance, blue-ringed octopus  ink contains tetrodotoxin,   the same deadly paralytic  found in the animal’s venom.  Researchers think its presence in ink  might slow or deter potential predators,   giving these small octopuses  even more opportunity to escape.

Similarly, some squids have toxins in their  ink that disorient predators. This seems to   buy them a bit more time, which can make a huge  difference if they have to outrun a fast attacker. And those amino acids?

They’re  believed to have a phagomimetic role.  That’s fancy biologist speak for  making the ink taste like food,   so predators try to eat it  instead of the actual animal! Though, that’s not the most elegant  way these animals can use their ink as a decoy. Remember how I said ink is a  mixture of mucus and pigment?  Well, sometimes cephalopods up the mucus  content a ton to make what scientists call   pseudomorphs: ink clouds that are roughly the same  size and shape as the creature who inked them!

These, no joke, seem to function as decoys.  The actual critter turns tentacle and runs,   leaving an inky shape behind  for a predator to attack.  Sometimes they even release  several pseudomorphs at once,   and then hide amongst them — which I assume  the predator just finds super confusing.  They can also make a slightly less mucousy  ink, which unfurls in long, ropey strands.   The animals tend to swim next to these, instead  of away from them, which seems counterintuitive. But researchers believe they do this  because these inky ropes resemble   something else — perhaps something dangerous like  a stinging siphonophore or jellyfish tentacles,   or just something inedible to  the predator, like seagrass.  And in that way, the critter is essentially  creating a place to hide in open water. Of course, all of what we’ve talked about so  far are variations on the smokescreen idea.  It turns out ink clouds can do more  than just help a cephalopod flee.  They also act as visual alarm cues  for others in the area.

That ink   cloud is a clear sign that there’s danger nearby. And scientists think the ink itself  may also serve as a chemical alarm.  The idea here is that nearby  cephalopods could smell   or taste that their cousin  is in trouble and, therefore,   danger is afoot — allowing them to high-tail it  out of there even if they can’t see the cloud! This could also explain why deep sea cephalopods   still ink, even when they live in  the darkness some 1800 meters down.  I mean, it’s not like a big dark  cloud or even a fancy fake squid   does much good in pitch blackness  when a predator can’t see them.

Though, there is one deep sea squid that’s  figured out how to use its ink more like its shallow water cousins.  It’s aptly named the fire-shooter  squid because it emits glowing ink! Other squid can make light with their bodies,  but this is the only one known to date which has   a light-producing organ that empties into their  ink sac, allowing them to squirt out luminous ink! This ink comes out as glowing ropes or  something resembling a shower of sparks,   and is likely used to blind or  distract a potential predator.  So, much like the toxic clouds and  pseudomorphs made by their shallower kin,   it gives the squid a headstart when fleeing.

But perhaps what’s really incredible  is that all of this is just part of the   story when it comes to the biology  and ecology of cephalopod inks.  Researchers are still working to fully understand   all the variations that are out  there and how the animals use them. One thing’s for certain though: the evolution of  ink and all of these creative takes has been key   to the success and survival of these  smart, boneless marine creatures. Thanks for watching SciShow!

If you liked this  episode, I bet you’ll love the one we did on   amazing things octopuses are teaching  us. So maybe, check that one out next!  And be sure to subscribe and  ring the notification bell   to catch all of our fun explorations of the  wild and wonderful world we get to call home. [♪ OUTRO].