How many hearts does an octopus have?

An octopus has three hearts. Two pump blood through the gills so it can pick up oxygen, and a third pumps that oxygenated blood around the rest of the body.

What's actually true

An octopus has three hearts. Octopuses run on a split circulatory system. Two hearts are dedicated to the gills, pushing blood through them so it can pick up oxygen. A third heart then pumps that freshly oxygenated blood around the rest of the body. It is one of many ways their anatomy differs from ours.

Takeaway: Great trivia comeback: an octopus has two hearts just for breathing.

Why people believe it

It sounds like a made-up trivia fact because one heart is so universal among the animals we know best, including fish, birds and mammals. Octopuses are distant relatives on the tree of life, closer to snails and clams than to us, and their bodies solved the same problems in different ways. The three-heart setup is a split circulation: the gill hearts boost blood through the gills, and the main heart handles the rest of the body.

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