Read & Think · Wild Science

Three Hearts, Blue Blood

Meet the octopus — the ocean's shape-shifting genius with eight minds of its own.

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A giant Pacific octopus photographed in a NOAA national marine sanctuary — the same eight-armed, three-hearted animal this piece explores. Photo: NOAA / National Marine Sanctuaries, public domain.

Imagine an animal with three beating hearts, blood as blue as the sky, and eight arms that each seem to make up their own mind. That animal is real — it's the octopus, one of the strangest and smartest creatures in the ocean.

Start with those hearts. An octopus has three hearts, and they split the work. Two of them pump blood to the gills, where the octopus pulls oxygen from the water so it can breathe. The third heart pushes that oxygen-rich blood out to the rest of the body.

Now the blood itself. Ours is red because it carries iron. An octopus's blue blood is built around copper instead. That copper is what turns the blood blue, and it helps the octopus move oxygen through cold, dark water where oxygen is hard to come by.

Then there are the arms — eight of them, lined with suckers all the way to the tip. A giant Pacific octopus can have up to 240 suckers on a single arm. Here's the wild part: each arm has its own brain. Add the main brain in the head, and an octopus has nine brains in total. That's why the arms can taste, grab, and explore almost on their own.

Maybe the most jaw-dropping trick is the vanishing act. In a blink, an octopus can change its color, shape, texture, and size. This is camouflage like nothing else in nature. It can copy other animals, melt into the rocks and coral, or bury itself in sand and shells until you'd swear it was never there.

The largest of them all is the giant Pacific octopus. Most weigh 30 to 50 pounds and stretch 6 to 8 feet across, but the biggest one ever caught, off Alaska, weighed over 600 pounds. Even so, these giants usually live just three to five years.

Three hearts, blue blood, nine brains, and arms with minds of their own. The octopus is proof that some of the most alien-seeming life on Earth is right here, hiding in plain sight.

Source: Facts from NOAA (National Oceanic and Atmospheric Administration), National Ocean Service and NOAA Fisheries — public domain.

Three Hearts, Blue BloodComprehension

Check that you read it

Fill each blank with the right word from the box.

Word bank: copper · gills · Alaska · brains · hearts

An octopus has three hearts, and they split the work of moving blood and oxygen.
Two hearts pump blood to the gills, where the octopus pulls oxygen from the water.
Instead of iron, an octopus's blue blood is built around copper.
Each arm has its own brain, so an octopus has nine brains in total.
The biggest giant Pacific octopus ever caught was found off the coast of Alaska.

Choose the best answer

Which sentence best states the main idea of the article?
- A. The octopus is a remarkable animal with unusual body systems and surprising abilities.
- B. Octopuses are dangerous and should always be avoided by swimmers.
- C. The giant Pacific octopus is the only octopus worth studying.
- D. Blue blood works better than red blood for every animal.
Why is an octopus's blood blue instead of red?
- A. It is built around copper instead of iron.
- B. It reflects the blue color of the ocean water.
- C. It is full of tiny air bubbles.
- D. It carries extra iron, unlike our blood.
Based on the article, why might an octopus's arms seem to 'think for themselves'?
- A. Each arm has its own brain.
- B. The arms are controlled by nearby fish.
- C. The arms are not connected to the body.
- D. The octopus has no main brain at all.

Three Hearts, Blue BloodVocabulary

Word cross

Use what you read to fill the puzzle. Every clue is answered somewhere in the article.

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3B

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Across

An octopus has three of these pumping organs.
The surprising color of an octopus's blood.
The metal that makes an octopus's blood blue.
The gas an octopus pulls from the water to breathe.
Two hearts pump blood here to collect oxygen.
Eight-armed sea animal at the center of this piece.
An octopus has eight of these, each with its own brain.

Down

A giant Pacific octopus can have up to 240 of these on one arm.
Counting one per arm plus the head, an octopus has nine of these.

Three Hearts, Blue BloodCritical Thinking

Now think

There isn't one right answer here. Explain your thinking — the reasons matter more than the answer.

1 · The article calls the octopus 'one of the strangest and smartest creatures in the ocean.' Which facts back up the 'smartest' part, and which back up 'strangest'? Could any single fact support both?

For the teacherA strong answer sorts specific evidence (nine brains and arms that explore on their own point to smart; three hearts, blue blood, and instant camouflage point to strange) and notices that a fact like 'each arm has its own brain' can support both claims at once.

2 · The article says copper 'turns the blood blue' AND 'helps move oxygen through cold, dark water.' Is being blue the reason octopuses survive deep water, or is the blue color just a side effect of the copper? Explain your thinking.

For the teacherA strong answer separates the color (an effect of the copper) from the function (copper carrying oxygen), reasoning that the blue is likely a side effect rather than the survival cause itself, and points to text to support it.

3 · An octopus can change its color, shape, texture, and size in a blink to hide. If you could give one human tool or machine that same camouflage power, what would you pick, what problem would it solve, and what could go wrong?

For the teacherA strong answer names a specific application, connects it to a real problem it would solve, and weighs at least one trade-off or downside, showing the student can transfer the article's idea to a new situation.