9 Fascinating Octopus Facts

This red octopus is one of about 3,300 species of cepahlopods alive today.
This red octopus is one of about 3,300 species of cepahlopods alive today. Photo © Noah Gubner / Getty Images.

Octopuses are a family of cephalopods (a subgroup of marine invertebrates) known for their intelligence, their uncanny ability to blend into their surroundings, their unique style of locomotion, and their ability to squirt ink. They are some of the most fascinating creatures in the sea.

01
of 09

Octopuses Technically Have Arms, Not Tentacles

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An octopus arm. Wikimedia Commons

The names may seem interchangeable to non-experts, but where cephalopods are concerned, marine biologists are careful to distinguish between "arms" and "tentacles." If the invertebrate structure has suckers along its entire length, it's called an arm; if it only has suckers at the tip, it's called a tentacle. By this standard, most octopuses have eight arms and no tentacles, while two other cephalopods, cuttlefish and squids, have eight arms and two tentacles.

02
of 09

Octopuses Squirt Ink to Defend Themselves

octopus
Wikimedia Commons

When threatened by predators, most octopuses release a thick cloud of black ink, composed primarily of melanin (the same pigment that gives human beings their skin and hair color). This cloud is not simply a visual "smoke screen" that allows the octopus to escape unnoticed; it also interferes with predators' sense of smell. Sharks, which can sniff small droplets of blood from hundreds of yards away, are especially vulnerable to this type of olfactory attack.

03
of 09

Octopuses Are Extremely Intelligent

octopus
Wikimedia Commons

Octopuses are the only marine animals, apart from whales and pinnipeds, of course, that demonstrate primitive problem-solving and pattern recognition skills. But whatever kind of intelligence these cephalopods possess, it's extremely different from the human variety. Two-thirds of an octopus's neurons are located along the length of its tentacles, rather than its brain, and there's no convincing evidence that these invertebrates are capable of communicating with others of their kind. Still, there's a reason so many science fiction movies (such as "Arrival") feature aliens vaguely modeled on octopuses.

04
of 09

Octopuses Have Three Hearts

octopus
Wikimedia Commons

All vertebrate animals have one heart, but the octopus is equipped with three: one that pumps blood through the cephalopod's body (including the arms), and two that pump blood through the gills, the organs that enable the octopus to breathe underwater by harvesting oxygen. And there's another key difference, too: the primary component of octopus blood is hemocyanin, which incorporates atoms of copper, rather than hemoglobin, which incorporates atoms of iron. This is why octopus blood is blue rather than red.

05
of 09

Octopuses Employ Three Different Means of Propulsion

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A swimming octopus. Wikimedia Commons

A bit like an undersea sports car, the octopus has three gears. If it's in no particular hurry, this cephalopod will walk lazily with its arms along the ocean bottom. If it's feeling a bit more urgent, it will actively swim by flexing its arms and body. And if it's in a real hurry (say, because it has just been spotted by a hungry shark), it will expel a jet of water from its body cavity and zoom away as fast as it possibly can, often squirting a disorienting blob of ink at the same time.

06
of 09

Octopuses Are Accomplished Mimics

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A camouflaged octopus. Wikimedia Commons

Octopus skin is covered by three types of specialized skin cells that can quickly change their color, reflectivity, and opacity, allowing this invertebrate to easily blend in with its surroundings. "Chromatophores" are responsible for the colors red, orange, yellow, brown, and black; "leucophores" mimic white; and "iridophores" are reflective, and thus ideally suited to camouflage. Thanks to this arsenal of cells, some octopuses can make themselves indistinguishable from seaweed.

07
of 09

The Largest Octopus Is the Giant Pacific

giant pacific octopus
The Giant Pacific Octopus. Wikimedia Commons

Forget all those movies you've seen in which an island-sized octopus, with tentacles as thick as a polar bear's trunk, sweeps helpless sailors overboard and swamps their vessel. The largest identified octopus is the Giant Pacific Octopus, the full-grown adults of which only weigh a puny 50 pounds or so and have long, trailing, 14-foot-long tentacles. However, there is some tantalizing evidence of larger-than-usual Giant Pacific octopuses, including one specimen that may have weighed as much as 500 pounds.

08
of 09

Octopuses Have Short Lifespans

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Wikimedia Commons

You may want to reconsider buying an octopus as a pet. Most species have a life expectancy of less than a year, and for a very gruesome reason. Millions of years of evolution have programmed male octopuses to die a few weeks after mating, and female octopuses stop eating while waiting for their eggs to hatch, starving themselves to death in the course of a few weeks. Even if you neuter your octopus (this procedure may not be offered by all veterinarians in your area), it's unlikely to outlast the average hamster or gerbil.

09
of 09

There Are Three Ways to Pluralize the Word 'Octopus'

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Wikimedia Commons

You may have noticed that this article refers to "octopuses," which strikes many ears as a bit awkward. It's also perfectly legitimate to say "octopi," even though this is a misuse of the classical plural Greek word structure ("octopus" is Greek for "eight legs") and outlawed by strict grammarians. If neither of these options appeals to you, you can also avail yourself of the lesser-used "octopodes," which refers to the larger order of cephalopods to which these creatures belong.