Two of an octopus’s hearts pump blood through the gills; a third pushes it around the body. When the animal swims, the systemic heart can pause — one reason crawling often beats jetting for efficiency.
Their blood is blue because of hemocyanin, a copper-based oxygen carrier instead of iron-rich hemoglobin. That chemistry works especially well in cold, low-oxygen seawater.
Three hearts and blue blood are not quirks for show. They are adaptations for an active, soft-bodied hunter that thrives where oxygen is scarce and pressure and temperature swing with depth.
Shahzad Mahota
Octopuses have three hearts and blue blood
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