The octopus, one of Earth’s oddest and most enduring creatures – they were here before dinosaurs – is spotlighted April 21 with NatGeo’s eye-opening “Secrets of the Octopus.”

These incredibly unique marine creatures have three hearts, blue blood and the ability to transform their bodies to mimic other animals. They can even communicate with different species.

But, notes Australian marine biologist and the show’s host Dr. Alex Schnell, “They are very sensitive to changes in their environment.  Changes in temperature can affect their appetite, their developmental rates, their sexual maturity.

“Amongst the 300 species of octopus, none of them are listed as vulnerable or threatened but given how sensitive they are to changes in their environment, there’s a huge risk that a lot of our species are going to be negatively impacted by the changes we’re seeing in the ocean.”

Schnell has been octopus obsessed since, “From when I can remember. I was lucky enough to grow up along the eastern beaches of Sydney where every octopus encounter cemented my path to be a marine biologist and study their behavior and their minds.”

If here before dinosaurs, why didn’t the octopus make the leap to walk on land?

“It’s just the evolutionary path that’s been taken. I mean, nature doesn’t make sense. Different critters on our planet come up with their own different solutions.

“Their ancestors mainly lived in the deep. They had a shell, but they lost that because they were living in pitch blackness. Then, octopuses that had no shell started infiltrating our oceans and now you’ll find them in every corner of the earth. In every ocean. Very different species but they all come up with these very innovative solutions to overcome the challenges that they’re faced with.”

Octopuses are, “Surprisingly bright,” Dr. Schnell learned. “People don’t expect that because an octopus doesn’t have a backbone. But they have an incredibly large brain. In terms of brain to body size ratio, the octopus’ is huge.

“And it’s very different to the brain that were used to seeing: It’s doughnut shaped, it’s wrapped around their throat and then it’s connected to these other clusters of brain cells that live at the base of the arm. So compared to the brain that we have in our head it’s spread out.

“But despite all these differences we’re seeing in terms of their physical appearance, physiology and even their behavior, we are seeing glimmers of intelligence that we once thought were unique to apes, to whales, to even crows and parrots!”

“Secrets of the Octopus” broadcasts Sunday on NatGeo and then streams on Disney+ and Hulu on Earth Day, April 22