Octopuses Have Three Hearts and Blue Blood
Close-up of an octopus swimming in deep blue water with its tentacles spread
These cephalopods have a central heart and two gill hearts. Their blood is copper-based, making it blue — more efficient for cold, low-oxygen deep-sea environments.
Why It’s Interesting
It challenges our mammal-centric view of biology. Copper-based blood is better adapted to extreme conditions, proving evolution finds wildly different solutions to the same problems.
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