Book 6, Question 34
Why Does an Octopus Have Three Hearts?
An octopus is a mollusk, not a fish, and it has three hearts. Two hearts serve the gills, and a third heart serves the rest of the body. That is one reason it is one of the most amazing animals in the sea!
From the book
Page from A Million Whys Book 6
More fun facts
- Two of an octopus's hearts pump blood past the gills to pick up oxygen.
- The third heart sends that oxygen-rich blood to the rest of the body.
- An octopus has blue blood.
- Two-thirds of an octopus's nerve cells are in its arms, not its head.
- Sea stars have no heart at all. They move seawater through their bodies instead.
- A fossil once called the earliest known octopus turned out not to be an octopus after all.
Sources: NOAA Ocean Service, Science News Explores, Smithsonian Magazine, Smithsonian Magazine
Questions kids ask
What color is octopus blood?
Blue.