Octopus: The Footed Void, at the New York Review of Books.
The closer you look at an octopus, the more you see.
Consider its anatomy: the “head,” a sack resembling a human scrotum that can shift through the entire color spectrum; the three hearts pumping blood that contains copper rather than iron; the eyes so very like human ones and yet radically more elegant in design. In a celebrated poem Ogden Nash begs the octopus to tell him if its limbs are arms or legs. Textbooks have a no-nonsense answer: they are arms, not legs (and emphatically not tentacles). But super tongues would be at least as good. Each octopus arm is a muscular hydrostat, like a human tongue, and each of the tens or hundreds of suckers on it is lined with tens of thousands of chemoreceptors—taste buds to you and me—and a comparable number of nerve endings that provide an exquisite sense of touch.
Or consider its intelligence.
More at the article.
Related viewing: This video from some years back.