Have you ever wondered which animals have 8 eyes? If so, you’re not alone – many people are fascinated by creatures with extra sets of eyes. In this article, we’ll explore the amazing animals that have 8 eyes and why they evolved this way.
If you’re short on time, here’s a quick answer to your question: Octopuses, along with other cephalopods like squid and cuttlefish, are the main animals that have 8 eyes. Their 8 arms each have a highly complex eye at the tip, giving them excellent all-around vision to detect predators and capture prey.
Below, we’ll take a deep dive into these incredible 8-eyed cephalopods. We’ll learn about their anatomy, evolution, behavior, and more. From giant Pacific octopuses to tiny octopus species, we’ll uncover why these brainy, color-changing animals developed 8 eyes instead of just 2 like us.
Let’s explore the mysteries of these alien-like creatures of the sea!
An Overview of Cephalopods and Their 8 Arms
Octopuses
Octopuses are a highly intelligent species of cephalopod mollusks that inhabit tropical and temperate ocean waters worldwide. They have 8 arms covered with suckers that are incredibly strong and enable them to taste, touch, and grab prey and objects.
Their arms are attached to a sack-like head and can regrow if lost. Octopuses have the rare trait of being able to fit through any hole larger than their beak. There are over 300 species of octopus identified so far, with the Giant Pacific octopus being the largest at 16 feet long according to the Smithsonian Ocean.
Octopuses are masters of disguise and can change both skin color and texture very quickly to match their surroundings as a defense mechanism. They have blue copper-based blood, three hearts, and a doughnut-shaped brain that allows them to have intelligence comparable to many vertebrates.
Known for problem-solving skills, an octopus in 2016 famously escaped its tank and slid down a 164-foot pipe to freedom.
Squid
Squids belong to a subclass of around 304 species of cephalopods closely related to octopuses. They inhabit oceans globally and come in a huge range of sizes from less than an inch up to 66 feet for the colossal squid.
Squids have fins on the sides of their mantles compared to octopuses and cuttlefish. They also differ with their 10 appendages – 8 arms and 2 longer feeding tentacles used to bring food to their beak-like mouths.
Squids move by jet propulsion, sucking water into their mantles and pushing it powerfully out of their siphons to propel themselves. They defend themselves by ejecting black ink clouds to confuse predators. Some squid species can fly briefly out of the ocean for distances over 30 feet.
Deep sea squids make up the largest portion of biomass on Earth according to AMNH.
Cuttlefish
Cuttlefish have a unique internal shell called a cuttlebone which they use to control buoyancy underwater. They have the amazing ability like octopuses and squid to adapt skin color, pattern, and texture almost instantaneously to disguise themselves from predators.
Cuttlefish propel with fin undulations and jet propulsion via their siphon and reach average lengths between 12-20 inches.
Cuttlefish are voracious predators with parrot-like beaks surrounded by 8 arms and 2 longer feeding tentacles. They have advanced camouflage capabilities, a sophisticated communication system via color and posture, and remarkable intelligence.
Cuttlefish can solve mazes, use tools, plan ahead, and outsmart prey according to research. Their large brain-to-body size ratio rivals octopuses in terms of intelligence.
The Anatomy and Capabilities of Cephalopod Eyes
Advanced Eye Structures
Cephalopods like octopuses, squids, and cuttlefish have incredibly advanced eye structures with capabilities rivaling most vertebrates. Their eyes contain components similar to human eyes – they have cornea, iris, crystalline lens, vitreous cavity, choroid, retina, and optic nerve.
However, there are some amazing differences that enable their fantastic vision.
While humans have a single lens in each eye, cephalopods have two lenses stacked on top of each other in each eye. This allows them to see extremely clearly both in water and air, with the ability to rapidly accommodate focus changes.
The lenses are spherical and much more pronounced than human lenses.
Wide Fields of Vision
Another incredible aspect of cephalopod vision is their exceptionally wide fields of view, nearing 360 degrees. Each eye can rotate independently, allowing the octopus to effectively see in all directions at once with just a slight head movement.
| Creature | Field of Vision |
| Octopus | Approaching 360 degrees |
| Humans | Around 180 degrees |
Researchers believe octopuses likely process visual information in a more parallel fashion compared to the sequential way humans process images. This massive visual data stream may be handled by the distributed computing power of the octopus nervous system.
Focusing and Depth Perception
The octopus lens system provides great ability to rapidly focus on objects at varying distances. Similar to humans, their eyes can change shape to focus light appropriately on the retina. However, their flexibility in lens accommodation exceeds the human eye – they can literally see clearly from inches to many feet away in an instant.
Their excellent depth perception likely comes from having two separate images in their brain that can be compared to estimate distance. This gives them precise ability to capture prey at the right moment.
According to the cephalopod research site The Cephalopod Page, some octopuses may also be able to perceive polarized light, which could aid in contrast and depth detection.
Seeing in Low Light
Finally, octopuses have excellent low light vision due to their high concentrations of rod cells in the retina. Coupled with the light gathering ability of their large lenses, this allows octopuses to see up to 1000 times better than humans in dark or murky waters!
The rods also enable excellent peripheral vision and motion detection abilities.
Octopuses achieve color vision via color filters in their skin above the retina, rather than colored retina receptor cells like humans have. By changing pigments in these filters, cephalopods can also adjust color vision to camouflage according to researchers from Cell Press.
The Evolution of 8 Eyes in Cephalopods
Origin as Molluscs
Octopuses, along with squids, cuttlefish, and nautiluses, belong to a class of marine animals known as cephalopods. Cephalopods evolved from ancient molluscs over 500 million years ago during the Cambrian explosion, when life on Earth diversified rapidly.
The earliest cephalopods had shells and tentacles but lacked complex eyes. Over millions of years, cephalopods adapted to become efficient hunters, developing complex brains, color-changing abilities, jet propulsion, and – perhaps most incredibly – camera-like eyes.
Development of Complex Eyes
The evolution of complex eyes allowed cephalopods to become formidable predators. Their eyes evolved independently from vertebrate eyes but have many similarities. Each eye contains a lens, iris, cornea, retina, and optic nerve.
Their retina contains photoreceptor cells called rhabdomes, which can detect light and send signals to the brain. Cephalopods also have an additional light-sensitive organ called the parapineal complex, which allows them to finely adjust vision in changing light conditions.
The structure of cephalopod eyes makes them exceptional at detecting movement and contrast, helping them hunt effectively.
Selection Pressures of the Ocean
Several evolutionary pressures selected for cephalopods to develop advanced vision. As carnivores, they needed acute eyesight to catch nimble prey like fish and crustaceans. Their eyes allow them to judge distance and movement precisely.
Cephalopods also live in dim ocean depths where vision is limited. Their large, sensitive eyes with excellent low-light capabilities help them see clearly where other animals cannot. Additionally, the ocean contains many camouflaged creatures.
Cephalopod eyes discern color, light, and patterns to spot hidden animals. Their evolving eyes were key to their survival in the challenging ocean environment.
Cephalopod Behavior and Their Use of 8 Eyes
Hunting, Prey Capture and Defense
Octopuses are amazing hunters, using their 8 eyes and color-changing abilities to great effect. Their eyes are complex – each one can focus independently, giving octopuses a nearly 360-degree field of vision to spot prey and predators.
When hunting, octopuses change color and texture to camouflage with their surroundings. Then they swiftly shoot out their arms to grab prey like crabs, shrimp, and fish. Their arms have powerful suction cups to grip prey tightly.
Once caught, prey is passed to the sharp beak to be torn apart and consumed.
Octopuses also use their color-changing abilities for defense. When threatened, they can quickly blend in with surrounding rocks or coral. Some species release ink clouds to confuse predators while they jet away.
The venomous blue-ringed octopus flashes bright blue rings to warn predators of its toxicity. So those 8 eyes not only help octopuses find food, but also help them avoid becoming food themselves!
Visual Communication
octopuses rely primarily on their excellent vision to communicate. By rapidly changing color and texture, they can convey a range of messages. For example, a male octopus will darken and develop reddish spots when confronting a rival. Females also use color to signal receptiveness during mating.
Impressively, octopuses can display different colors and patterns on different parts of the body simultaneously. So their 8 widely spaced eyes allow them to send visual signals in several directions at once – a handy talent!
Octopuses also communicate through visual displays like stretching their arms or puffing their Mantle. Displays like the ‘moving wall’ and ‘passing cloud’ are used during courtship. Researchers have identified up to 38 distinct body patterns used for communication.
Having 8 eyes enhances octopuses’ ability to both send visual signals and monitor each other’s responses. Their excellent vision is key to their sophisticated visual language.
Camouflage and Color Changing
One of the most astounding octopus abilities is their remarkable color-changing camouflage. They can almost instantaneously match the color, pattern and even texture of their surroundings. This helps them avoid predation and surprise prey. So how does having 8 eyes aid their camouflage skills?
Octopuses have specialized skin cells called chromatophores that allow rapid color changes. Their 8 widely-spaced eyes provide a panoramic view to closely monitor their surroundings. This helps them accurately match backgrounds.
Each eye also has an exceptional ability to discern color, texture, and patterns. Moreover, having independent eye control likely aids in depth perception and detecting contrasts that reveal the octopus’s outline.
So while all cephalopods possess color-changing abilities, octopuses’ 8 keen eyes make them the masters of disguise.
Unique Cephalopod Species and Their 8 Eyes
Giant Pacific Octopus
The Giant Pacific octopus (Enteroctopus dofleini) is the largest known octopus species in the world, growing up to 16 feet in length and weighing up to 110 pounds. These enormous cephalopods inhabit the northeastern Pacific Ocean along the coasts of America and Canada.
Like all octopuses, they have eight arms covered with suckers and a beak-like mouth. Their most distinguishing feature is the eight eyes, allowing them to see very well underwater. Giant Pacific octopuses are quite intelligent, known for problem-solving skills and short-term memory retention.
Some key facts and statistics about the Giant Pacific octopus include:
- Lifespan: 3-5 years on average
- Habitat range: Intertidal zone down to 1900 meters depth
- Diet: Crustaceans, mollusks, fish, and sometimes even sharks and birds
- Enemies: Sperm whales, elephant seals, sea otters, wolf eels
- Camouflage experts – can change skin color/texture to blend into surroundings
Unfortunately, Giant Pacific octopus populations have been declining in recent decades, primarily due to overfishing, pollution, and climate change impacting their habitat. Several conservation efforts are underway to better protect this fascinating 8-eyed creature in the wild through marine protected areas and sustainable fishing regulations (Oceana.org).
Humboldt Squid
The Humboldt squid (Dosidicus gigas) is an aggressive predator found in the Eastern Pacific waters along the west coast of the Americas. These mean-tempered mollusks grow up to 6 feet long and weigh over 100 pounds.
They earned the nickname “red devils” for their blood-red skin coloration and volatile nature. Humboldt squid travel in large shoals and ambush prey using their 8 arms and suckers. They have excellent vision from their two camera-like eyes, able to see color and light/dark contrasts.
Humboldt squid have expanded their habitat range in recent years, a phenomenon linked to warming ocean waters and declining fisheries. Some key statistics on these prolific cephalopods include:
- Lifespan: Typically 1-2 years
- Swim speed: Up to 15 mph in short bursts
- Annual population: Possibly over 100 million individuals
- Beaks sharp enough to puncture heavy wetsuits
- Bioluminescent photophores along body for counter-illumination camouflage
While Humboldt squid are not currently considered threatened, their populations do fluctuate substantially each year depending on water temperatures and food availability. Their rapid reproduction and adaptation to environmental changes ensure these 8-eyed ocean predators will continue thriving (MontereyBayAquarium.org).
Mimic Octopus
The Mimic octopus (Thaumoctopus mimicus) is a talented shapeshifter earning fame across the underwater world. Found in tropical Indo-Pacific waters, it earns its name from an incredible ability to imitate the appearance and movements of other sea creatures.
This brilliant invertebrate can contort its soft body into various shapes while changing color/texture patterns for disguise. It has great eyesight from those trademark octopus peepers to closely observe organisms it wants to impersonate.
Some of the amazing impressions in the mimic octopus repertoire include:
- Sea snakes – by forming a long thin shape
- Lionfish – by spreading web between arms
- Jellyfish – by billowing arms/web and pulsing along
- Crabs – shapes an arm into a claw and walks on seabed
- Sea stars – curls arms together and moves stiffly like one
First discovered in 1998, there is still much to uncover about the full capabilities of this highly intelligent 8-eyed master of disguise. Its incredible adaptable form and behaviors showcase the evolutionary wonders made possible through natural selection (Oceana.org).
Protecting the fragile coral reef ecosystems this shy octopus calls home is vital for the species’ conservation in the changing ocean environment.
Conclusion
In closing, cephalopods like octopuses, squid and cuttlefish offer astounding examples of just how useful it can be to possess 8 eyes. Their eye structures and placement supports exceptional vision from all angles, allowing them to expertly hunt, avoid predators, communicate visually and camouflage themselves in their marine environments.
Researchers continue uncovering new insights into these animals and their biological innovations. Octopuses in particular continue intriguing scientists with their intelligence, problem-solving skills and personalities.
While land animals evolved with just two eyes, cephalopods found an advantage underwater through their 8-eyed anatomy. These multi-eyed creatures of the sea will likely continue inspiring imagination and discovery about the many successful evolutionary paths life can take.
