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The ocean is filled with strange and fascinating life forms, but few are as extraordinary as the octopus. With remarkable intelligence, the ability to blend seamlessly into their surroundings, and features that seem almost alien, octopuses stand apart from all other creatures. What makes them even more astonishing is their unusual biology — they possess not just one brain, but nine, and three hearts instead of one.
This article dives into the unusual anatomy of the octopus, exploring how these incredible adaptations evolved and what they reveal about intelligence, survival, and life in the depths of the sea.
Understanding Octopus Anatomy: A Quick Overview
Octopuses are soft, eight-armed sea creatures that belong to the same family as squid, cuttlefish, and nautiluses, all part of the group called Cephalopods. With no internal skeleton and the ability to squeeze through tiny spaces, octopuses are masters of survival. But what truly sets them apart is their complex nervous and circulatory systems — unlike anything seen in vertebrates like mammals or birds.
Let’s break down the two most extraordinary aspects of their internal anatomy:
- They have nine brains in total — one main brain in their head plus a smaller brain in each of their eight arms.
- 3 hearts (2 branchial hearts + 1 systemic heart)
Why Does an Octopus Have 9 Brains?
Octopuses are often referred to as the “smartest invertebrates,” and with good reason. They exhibit problem-solving abilities, short- and long-term memory, tool use, and even individual personalities. But to support their incredibly flexible and autonomous limbs, evolution gave them a radically different nervous system than anything we’re familiar with.
Here’s how their 9-brain system works:
- Central Brain (1):
Located between the octopus’s eyes, this doughnut-shaped brain controls higher cognitive functions such as learning, memory, decision-making, and complex behaviors like escaping predators, camouflage, and hunting strategies. - Peripheral Arm Brains (8):
Each of the octopus’s eight arms has its own little brain, called a ganglion, that can move the arm on its own without needing directions from the main brain. This decentralized nervous system gives octopuses an almost robotic level of autonomy.
Fascinating Facts:
- An octopus’s arm can taste, touch, and even react to stimuli independently of the main brain.
- Even if severed, an octopus arm can continue to respond to touch and move on its own for a short time.
- Almost two-thirds of the octopus’s brain cells—about 500 million—are found right in its arms.
This multi-brain setup is not about intelligence per se, but about distributed control — allowing the octopus to multitask efficiently. For example, an octopus can open a shell with one arm while exploring a new area with another, and while the central brain may be focused elsewhere.
Why Does an Octopus Have 3 Hearts?
Octopuses also boast a three-heart circulatory system, which supports their highly active and oxygen-demanding lifestyle. As cold-blooded animals with high metabolic needs, especially during fast movement or camouflage, multiple hearts provide the necessary circulatory efficiency.
Breakdown of the octopus heart system:
- Two Branchial Hearts (2):
These hearts are responsible for pumping blood through the gills, where oxygen is absorbed. Each branchial heart supplies a separate gill. - One Systemic Heart (1):
Once the blood is oxygen-rich, the primary heart circulates it throughout the body, delivering oxygen to the organs and tissues.
An Interesting Twist:
- When an octopus swims, the systemic heart temporarily stops beating — which is why swimming is so energetically costly and why octopuses prefer to crawl.
- Their blood uses hemocyanin, a copper-based molecule that makes it blue, instead of the iron-based hemoglobin found in most animals. This helps them survive better in cold places with little oxygen.
Evolutionary Advantages of 9 Brains and 3 Hearts
1. Survival and Reflexive Autonomy
- Independent arm brains allow octopuses to react to threats or stimuli without needing to send signals back to the central brain.
- This setup reduces reaction time, which is critical when escaping predators or manipulating complex environments.
2. Efficient Blood Circulation
- Having three hearts ensures that even the most remote tissues receive adequate oxygen.
- This is crucial for an animal with no skeleton and constantly moving limbs, particularly during intense activity.
3. Advanced Problem Solving and Behavior
- The central brain’s cognitive power lets octopuses solve puzzles, escape enclosures, mimic other animals, and interact with humans.
- Combined with arm autonomy, this allows for incredibly coordinated movement and multitasking in real-time.
Intelligent Aliens of the Deep?
Octopuses are often described as “aliens” on Earth — and for good reason. Their intelligence, decentralized nervous system, and ability to change shape and color are so unique that some scientists even question whether octopus evolution followed a completely different path from most other animals.
Consider These Amazing Octopus Behaviors:
- Opening jars to retrieve food
- Escaping from aquarium tanks
- Using coconut shells or rocks as shelters, showcasing their ability to use tools.
- Changing color and texture for camouflage within milliseconds
- Displaying short-term and long-term memory in lab experiments
This level of conscious behavior and awareness — in an animal that split from humans evolutionarily over 500 million years ago — challenges everything we know about what constitutes “intelligence.”
What Can Humans Learn from Octopus Anatomy?
1. Decentralized Intelligence
- Understanding how octopus arms function independently could influence robotics, AI, and biomimetic designs for flexible machinery.
2. Redundancy in Systems
- The octopus’s three-heart system shows how biological redundancy can enhance survival — a lesson applicable to medical and engineering systems.
3. Blue Blood Efficiency
- Studying how hemocyanin works in low-oxygen environments may offer insights into human medicine or deep-sea exploration gear.
