Get ready to count: one, two, three! An octopus has three hearts. And its closest relatives, squid and cuttlefish, have three hearts too.
Each heart has a job. Two of the hearts work only to move blood past the octopus's gills. There, the blood lets go of carbon dioxide and picks up oxygen. Then the third heart sends that oxygen-rich blood out to the organs and muscles, giving them energy. That third heart sits in the middle of the octopus's body. An octopus scientist says it is the largest and most muscular of the three.
Now for the wild part. That big main heart actually stops beating when the octopus swims! Swimming wears an octopus out. That helps explain why octopuses would rather crawl than swim.
And their blood? It's blue! Octopus blood carries oxygen with a special protein called hemocyanin, and that protein has copper in it. In sea animals, hemocyanin has no color at all. But when it grabs onto oxygen, it turns blue. Squid and some crustaceans have blue blood too.
So here's a question for you: if you had three hearts, what job would you give each one?
