Mind-blowing facts about this alien-looking creature that's one of the hardest to study in the wild

With their eight arms and giant egg-shaped head, octopuses are one of the most alien-looking creatures on the planet.

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 world 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.

Octopuses are solitary creatures who spend most of their lives swimming alone, even when it comes time to mate.

Image courtesy of NOAA Okeanos Explorer Program, Our Deepwater Backyard: Exploring Atlantic Canyons and Seamounts.

Octopuses have three hearts. The main heart will actually stop beating when the animal is swimming, so it can't swim very far before tiring out.

But walking is slow and makes the octopus vulnerable to predators. As a result, some octopuses carry protection with them. Here an octopus is transporting two empty coconut halves it can hide inside if necessary.

Octopuses' most impressive survival tactic is their skin: They can change the colour and texture of their skin to blend in with their surroundings and avoid detection. Can you spot the octopus in this photo?

Greg Deocampo on YouTube

They can complete a full-body transformation in just three tenths of a second using the three different colour-changing sacs in their skin: chromatophores, iridophores, and leucophores. Most other animals who can change colour have only chromatophores.

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