Everything You Need to Know About Octopuses
Introduction
Octopuses, those fascinating and often misunderstood cephalopods, capture our imaginations with their unique anatomy, remarkable intelligence, and mysterious lives in the ocean's depths. Often seen as creepy or mysterious, these creatures have inspired countless myths and legends, from the Kraken to Ursula the sea witch. But octopuses are far more than just monsters or curiosities. They are intelligent, anatomically unique creatures that have inspired both ancient Greek philosophy and Japanese erotic art. Let's delve into the world of octopuses and uncover some amazing facts about these incredible animals.
Octopus Ancestry and Evolution
The history of octopuses stretches back millions of years. The oldest known fossil of an octopus ancestor lived approximately 330 million years ago, long before the dinosaurs roamed the Earth. This fossil, discovered in Montana’s Bear Gulch limestone formation and described in 2022, reveals that ancient octopuses had ten limbs, unlike the eight arms of modern species. Previously, the oldest octopus fossil was a 296-million-year-old invertebrate called Pohlsepia mazonensis. Despite being described as a “cow patty-flattened out into a globular splat,” a close examination revealed its eight arms, two eyes, and possible ink sac.
Anatomy and Physiology
Three Hearts
Octopuses have a unique circulatory system featuring three hearts. Two of these hearts, known as branchial hearts, are dedicated to pumping blood through the gills, where carbon dioxide is released, and oxygen is absorbed. The third heart, called the systemic heart, circulates the oxygen-rich blood to the rest of the body, providing energy to the organs and muscles. This three-heart system is good at keeping blood pressure up. Branchial hearts pump blood through the gills to get oxygen, but octopuses still need a big heart to pump the blood around the rest of the body.
Blue Blood
Instead of iron-based hemoglobin like humans, octopus blood relies on a copper-containing protein called hemocyanin to transport oxygen. This hemocyanin makes their blood appear blue when oxygenated. Hemocyanin is more efficient than hemoglobin at carrying oxygen molecules in cold water and low-oxygen conditions. This adaptation is essential for survival in the deep ocean, where temperatures are low, and oxygen is scarce. However, this also makes octopuses highly sensitive to changes in acidity, as a drop in pH can hinder their ability to circulate enough oxygen.
Distributed Intelligence
An octopus's intelligence isn't confined to its brain. In fact, two-thirds of an octopus’ neurons reside in its arms, not its head. This decentralized nervous system allows each arm to function somewhat independently. Individual arms can taste, touch, and move without direction from the central brain, though the central brain is capable of taking control of the arms as well, according to the Natural History Museum. Octopus arms can figure out how to crack open a shellfish while the rest of the animal is busy doing something else, like checking out a cave for more edible goodies. Octopus tentacles can even react after they’ve been completely severed from a dead animal.
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The Beak
All cephalopods, including octopuses, have beaks that resemble a parrot's beak. The common octopus has a two-part beak which it uses to eat crunchy prey like crabs and clams. Mostly made of chitin, the beak is indigestible, meaning you could tell if a predator snacked on an octopus!
Intelligence and Behavior
Problem Solvers
Aristotle famously dismissed octopuses as stupid, but modern science has proven otherwise. Octopuses possess remarkable intelligence. They have big brains for their size, and they’re able to figure things out, like how to open a clamshell that’s been wired shut. They can navigate mazes, solve problems, remember solutions, and even take things apart for fun. Octopuses even have distinct personalities, as explored in the Oscar-winning documentary My Octopus Teacher.
Camouflage and Self-Protection
Octopuses are masters of camouflage and have evolved an array of tricks over tens of millions of years to avoid or thwart would-be attackers. They can match the colors and even textures of their surroundings, allowing them to hide in plain sight. This is accomplished through a network of pigment cells called chromatophores within its skin. The common octopus has mastered this camouflage so well that even the fiercest of predators can swim right by without noticing!
If a predator gets too close octopuses can escape quickly, shooting themselves forward by expelling water from a muscular tube called a siphon. Octopuses can also release a cloud of black ink, which obscures them and dulls an encroacher’s sense of smell. Their ink even clouds a predator’s sense of smell, making it more difficult to follow the escaping octopus! This ink is a mixture of mucus and melanin, the same substance that provides pigment in human skin, hair and nails. The ink also physically harms enemies. It contains a compound called tyrosinase, which, in humans, helps to control the production of the natural pigment melanin. But when sprayed in a predator’s eyes, tyrosinase causes irritation.
Their soft bodies mean octopuses can fit into impossibly small nooks and crannies, as long as the holes are not smaller than the only hard parts of their bodies: their beaks. If all else fails, octopuses can lose an arm to an attacker and regrow one later.
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Social Interactions
Octopuses are usually solitary animals that live alone, but that doesn't mean they aren't social. Males and females communicate with each other through displays, potentially to attract mates but also to show aggression. In Australia, gloomy octopuses signal aggression by making themselves darker and sometimes climbing on top of ship wreckage so they're taller. They've also been recorded flinging shells and sand at each other.
Octopuses each have their own personalities. For example, some octopuses kept in aquariums are very keen to interact with their human keepers, while others aren't bothered. Captive octopuses have even been known to develop a dislike for certain people but not others.
Tool Use
Scientists have observed octopuses demonstrating a variety of learning characteristics, such as the use of tools. For example, an octopus may find a discarded coconut husk and use it as a shelter. Octopuses have also demonstrated the ability to manipulate objects by pushing, pulling and even twisting things like jar lids!
Reproduction and Life Cycle
Mating and parenthood are brief affairs for octopuses, which die shortly after. The species practices external fertilization. A male inserts his spermatophores directly into the female’s mantle cavity, using his hectocotylus, a special, longer arm. Afterward, the male’s “sex arm” falls off, and the animal dies. Instead, male octopuses use a modified arm-called a hectocotylus-to pass sperm to the female octopus, and the appearance varies between octopus species. Some species, such as paper nautiluses, leave their sexual appendage behind as they jet away.
As for the females, they can lay up to 400,000 eggs, which they obsessively guard and tend to. Eggs are laid in strands attached to substrate in shallow waters. The female then cares for the eggs and stands guard until they are all hatched. To prioritize their motherly duties, females stop eating. By the time their eggs hatch, female octopuses are either dying or dead. Their optic glands rapidly produce self-destructive chemicals, causing a rapid change in cholesterol metabolism and ultimately killing them.
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Octopuses are considered semelparous animals, meaning they only reproduce once in their lifetime. So while they may not have long lives, we can be confident that the octopus plays an integral role in the ocean ecosystem in which they thrive.
Newly hatched octopuses, called larvae, are mere millimeters in length!
Habitat and Distribution
There are around 300 species of octopus and they are found in every ocean. They live in oceans around the world, from the frigid waters of the Arctic and Antarctic, to the warm waters of the tropics. Most live on the seafloor, but some, like the paper nautilus, drift nearer to the surface. Different octopus species are adapted to life in different conditions, such as coral reefs or the deep sea. Dumbo octopuses - named for their big ear-like fins resembling the Disney elephant - live at the deepest depths. In 2020, researchers filmed a dumbo octopus 4.3 miles (6.9 kilometers) beneath the surface of the Indian Ocean - nearly twice as deep as the wreck of the Titanic.
Diet
Octopuses are carnivores, so they eat meat. They mostly feed on crabs, shrimp, and mollusks. Their diet includes fish, clams, shrimp, crabs and even other octopuses. They change their hunting tactics depending on what they're eating. For example, an octopus will pounce like a cat on crabs, while it's more cautious with shrimp, leading with just one arm so as to not spook its dinner. Some octopuses team up with fish they don't eat to find smaller prey they do eat. Octopuses can cover more area hunting with a group of fish and increase their chances of a catch. However, octopuses can be irritable hunting partners. Researchers have observed big blue octopuses using their arms to punch fish they're hunting with in the head. A 2024 study found that octopuses most frequently hit blacktip groupers, which weren't very good hunting partners.
Relationship with Humans
Culinary Delicacy
Octopuses are consumed as food in many parts of the world. But such culinary prevalence has had an impact on octopus populations around the world. The international demand for octopus inspired North and West African fisheries to start targeting the animals in the 1980s, and overfishing in those waters has shifted the industry from Morocco to Mauritania and, more recently, Senegal.
Cultural Significance
Octopuses have also inspired art and literature throughout history. “Tentacle erotica” goes as far back as a sensual 1814 woodblock print, published in Katsushika Hokusai’s Kinoe no Komatsu collection of erotic books. According to Harmon Courage, the image takes inspiration from a legend about a female shell diver who is chased by sea creatures, including octopuses, after attracting the eye of a sea dragon god. As Japanese art curator Ann Yonemura wrote for the Pulverer Collection, the 1814 print referred to a longtime erotic association with abalone divers.
Ethical Considerations
Octopuses are typically submerged in a freezing “ice slurry” of 26 degrees Fahrenheit, causing an incredibly slow and stressful death. A study on this method found that when an octopus’s body drops below 30 degrees, their muscles revert to a state that resembles unconsciousness or death-but they are very much still alive, leading to possibly severe pain.
As we’ve learned in this blog, octopuses are keenly aware of the fact they’re in captivity. These animals suffer immensely in captivity, such as zoos and aquariums, but companies are also trying to open octopus factory farms. Octopus farming is so immensely cruel that states are preemptively banning the process because there’s simply no humane way to keep these animals in captivity.
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