Cephalopod facts

Himadri has just said my blog is becoming more esoteric by day. 
I suppose it is. 
The thing with me is, if I’m fascinated by something, I want to know more and more about it. I love Moby Dick for example, so I read Philip Hoare’s book about whales, watched Blue Planet about whales, and went whale-watching in Whitby, and I read other works by Melville. Or I discovered Ingmar Bergman, so now I’ve seen 17 films by him, read his biography The Magic Lantern, and read multiple books about his works. 
Certain things wear off after some time, like with whales, but it was fun whilst it lasted (my love for Melville remains, though). 
So, back to cephalopods—this class includes octopuses, cuttlefish, squids, and nautiluses. 
Squids: 



2 tentacles and 8 arms 
Have ink 
In Vietnamese, squids are called mực, which means ink 
Blue-green blood
Can change colours but not as well as cuttlefish
3 hearts  

Cuttlefish: 



2 tentacles and 8 arms 
The most colourful of cephalopods
W-shaped eyes 
Colour-blind 
Have a cuttlebone 
Have ink 
In Vietnamese, also called mực (like squids), which means ink 
Blue-green blood
3 hearts
Unlike octopuses, cuttlefish don’t tend their eggs but glue them to rocks and leave them

Octopuses: 



8 arms (though some scientists say 6 arms and 2 legs) 
Can smell and taste with their arms 
3 hearts 
Have ink 
Blue-green blood
Less colourful than cuttlefish but have no bone, can take almost any shape and can change texture of their skin
Master of camouflage  
Colour-blind 
Horizontal pupils 
Highly complex nervous system (500 million neurons) 
Females tend their eggs for their remaining days and die 
Smartest of cephalopods: can solve puzzles, recognise individual humans, open a jar from inside, fit through anything as long as the beak fits, use tools, manipulate objects, and so on.  
Also, I didn’t think I’d ever say this, but this is a very beautiful octopus:





The octopus is called Freya and this was at New England Aquarium, the one mentioned in The Soul of an Octopus.

Nautiluses: 



I know absolutely nothing about them except that they have shells and have remained relatively unchanged for millions of years (the closest to the 1st cephalopods that appeared, compared to octopuses or cuttlefish). 
Compared to other cephalopods, they’re not particularly smart, and therefore not really interesting.  



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Look at this sad passage from Other Minds, chapter 7, “Experience Compressed”: 

“A strange-looking rock-dwelling fish that inhabits the same patch of sea as my cephalopod is from a group that includes fish who live to 200 years of age. 200! This seemed extraordinarily unfair. A dull-looking fish lives for centuries while the cuttlefish, in their splendor, and the octopus, in their curious intelligence, are dead before they are 2?” 

What is the point of such a complex nervous system when they have a lifespan of 2-3 years? Their intelligence just goes to waste. 
Peter Godfrey-Smith goes on: 

“Nautiluses, the elegant but psychologically unimpressive cephalopods who steer their shells like submarines around the Pacific, can live for more than 20 years. That is several drawn-out decades of life for what biologists, unflatteringly, have called a “smell-and-grope scavenger”. These animals are relatives of octopuses and cuttlefish, and they are not rushing through their lives at all.” 

This is ridiculous.