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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!
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to catch all of our fun explorations of the wild and wonderful world we get to call home.
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