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The Pinnacle of the Invertebrates

#1
Yazata Offline
In her very engaging popular science book Squid Empire - The Rise and Fall of the Cephalopods, Danna Staaf calls squid: "swimming protein bars".

"Pretty much every animal that encounters a squid tries to eat it... the poor things are born delicious"  and "Back in the 1980s, scientists calculated that the mass of cephalopods eaten by whales, seals and seabirds outweighed the total marine catch (fish, cephalopods, and everything) of all fishing fleets around the world."

"Squid have brains too, but instead of a double-hemisphered lump, they come in three parts: one optic lobe behind the left eye, another optic lobe behind the right eye, and between them a strangely shaped doughnut of nervous tissue. Through the doughnut runs the squid's esophagus. This is the most direct route from the mouth into the mantle, where the stomach and other organs lie, but as you might imagine, swallowing through your brain can be risky."


But despite their dangerous lives, these animals have managed to survive in one form or another since the Cambrian period 500 million years ago when multicellular animals were newly arrived in what had hitherto been a world of microorganisms. They were the most advanced animals and the top predators in the oceans in those early days and fish with bony jaws probably evolved to exploit them. (Then some of those fish hauled themselves out of the sea, turned into terrestrial tetrapods and ended up as us.) But the cephalopods remained,  constantly evolving to become smarter and smarter in an unceasing undersea arms race, as predators in an ocean where seemingly everything wanted to eat them back, and managed to survive all the mass extinctions and here they are, including the octopuses who are probably the most intelligent and sentient of the invertebrates (perhaps even rivaling dolphins in their space-alien way). Jet-propelled snails.

"Cephalopods became the first creatures to rise from the seafloor, essentially inventing the act of swimming. With dozens of tentacles and formidable shells, they presided over an undersea empire for millions of years. But when fish evolved jaws, the ocean's former top predator became its most delicious snack. Cephalopods had to step up their game."

https://www.amazon.com/Squid-Empire-Rise...ephalopods

Regarding octopus intelligence, the book to read is Peter Godfrey-Smith's Other Minds - The Octopus and the Evolution of Intelligent Life.

"What if intelligent life on Earth evolved not once, but twice? The octopus is the closest we will come to meeting an intelligent alien. What can we learn from the encounter? Tracking the mind's fitful development from unruly clumps of seaborne cells to the first evolved nervous systems in ancient relatives of jellyfish, he explores the incredible evolutionary journey of the cephalopods, which began as inconspicuous molluscs who would later abandon their shells to rise above the ocean floor, searching for prey and acquiring the greater intelligence needed to do so - a journey completely independent from the route that mammals and birds would later take."

https://www.amazon.com/Other-Minds-Octop...B01LXKA6FO
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#2
Syne Offline
Cuttlefish are by far the smartest cephalopods. Octopi just have greater terrestrial mobility.
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