Yet scientists have an extremely difficult time studying them in the wild because these highly intelligent invertebrates are the ultimate masters of disguise.
In her book, "Octopus!" Katherine Harmon Courage travels the globe to swim, observe, and even taste some of the many octopuses of the world. Here are 30 mind-blowing facts she learned about this squishy predator of the sea along her epic journey.
Over 95% of all animals on Earth are invertebrates. The octopus is the smartest of them all and has approximately 300 million neurons throughout its body. That's not much compared to the 100 billion in humans, but it's a giant leap from the 16 million in frogs.