Octopus Information for the Discerning Reader
In appearance an octopus is essentially a brain sac with eight arms attached anteriorly (That’s science talk for in the front). The beaked mouth is located ventrally (on the bottom), with two eyes located high on both sides of the brain sac.
As their name implies, all octopi have eight arms, not tentacles (tentacles are longer and only have suckers at the ends.) This is even true of species in family Allopsidae which are commonly named the Seven Armed Octopi. The name Seven Armed Octopus arose because the arm specialized for mating is reduced in size and hidden from view when not in use (I'll bet you always wondered why the seven armed octopus wasn't just called the septipus). Almost all octopod arms are lined with suction cups, usually a double row.
With the exception of suborder Cirriata, octopus bodies have no rigid structures of any sort, such as bone or shell, apart from one sharp parrot-like beak.
Like other cephalopods, octopi have an efficient closed circulatory system (blood stays in the blood vessels unless something has gone very wrong). The octopus’s blood is pumped through its body with three separate hearts: one branchial heart for each of its two gills and an additional heart for pumping the blood through the rest of the body.
In order to circulate enough water over their two gills, located in the mantle cavity (its like a ghetto lung), and to maintain their active predatory lifestyle, octopi contract the muscles in their mantle wall (sort of like a diaphragm).
At least as intelligent as the average housecat, octopi are easily the smartest of all invertebrates (by a whole lot). Proven to have both short and long term memories and possessing astonishing problem solving skills (one can solve a rubix cube), octopi are even advanced enough to manipulate foreign objects.
This intelligence combined with octopus curiosity make octopi a very stressful animal to keep in captivity even for professionals in major aquariums (they like to take things apart and they're wicked strong). A favorite example of this is the exploits of an octopus from the Vancouver aquarium they named Houdini. At the aquarium several years ago the staff were perplexed when fish started disappearing from their tanks without a trace. The staff searched the tanks of the disappeared fish thoroughly but found no fish bodies or animals that could have eaten the fish. Suspecting that someone may have been coming in at night and stealing the fish, staff members set up video cameras by several of the tanks. The video from one tank revealed Houdini, who already had a reputation for figuring out ways to get out of his tank, coming out of the water circulation pipes eating the fish and crawling back into the pipe. It turned out that the octopus had managed to remove the screen from the filtration pipes in his enclosure, crawl through the system of pipes into other tanks and amazingly remember the numerous turns and pipe changes to return to his own tank (Mario ain’t got shit). This was not the first time Houdini had paid other tanks a visit to expand his cultural horizons and eat their inhabitants.
Jacques Cousteau (the underwater Carl Sagan), through his famous crayfish in a jar experiment, found octopi capable of learning by observation (essentially they can do science). An octopus was given a sealed jar with a super delicious crayfish inside, it proceeded to bear-hug the shit out of the jar to no avail. Next they took the jar and unscrewed the lid as the octopus watched. They then gave the octopus a second jar with a crayfish in it, the octopus immediately unscrewed the lid and enjoyed crayfishy bliss. There is video of an octopus grabbing both halves of a split coconut from the ground and closing them around itself when it felt threatened (that's right an octopus using body armor).
This level of intelligence is due to the octopus’s complex nervous system, only a third of which is centralized in the brain. The nervous system of octopi, though effective, is vastly different from that which has arisen in vertebrates. Vertebrates are always aware of how every portion of their body is positioned, in other words they always have a mental picture of their entire body. A person doesn’t have to look at their knees to know if they are bent or not, or look at their hand to determine the shape of something they are holding. This is called stereognosis and is possible because large portions of the cerebral cortex are dedicated to processing all the individual muscle contractions, relaxations, and adjustments needed to carry out the commands of the brain. When a person makes a fist, the brain calculates the commands each of the muscles on each finger by just the right amount needed to make a fist. This is possible because of the extremely limited range of motion allowed by a skeletal system.
On the other hand, octopi lack stereognosis. Because of the completely unlimited range of motion on each of their eight arms, they can bend any and every part of their arms in any direction. This means that the octopus’ brain is nowhere near big enough to process all of the sensory input stereognosis would require (at a certain point everyone has to know when to delegate tasks). The octopus nervous system, rather than rely on the brain to process the minute details of how to carry out commands, has extensive nerve cords in each of its arms to carry out the details of a command from the brain. The brain only gives general instructions on what to do without knowing how to do them, whereas the arms “know” how to do; the brain takes for granted that the arm is doing it. As such, the octopus brain won’t know what an arm is doing unless it can see the arm. This has some benefits as octopi can perform several complex tasks with each arm at the same time and still keep a look out for food or danger. (a human punches someone whereas an octopus has his arm punch someone)(automatic transmission vs stick shift).
Octopi primarily use two forms of locomotion: crawling and jet propulsion, they can swim with their arms but rarely do so because swimming out in the open is dangerous (with 8 arms NOT climbing everywhere would seem like a waste). Under most circumstances octopi use their arms to pull themselves along a solid surface, be it the sea floor or a reef. When speed is required, octopi are capable of jet propulsion by expelling the water from the mantle cavity through their funnel. (Picture a spider monkey with a ski-do strapped to his ass.)
Octopi are predators and will eat most anything that isn’t bigger than them (an octopus is always the strongest, smartest, and fastest thing in its weight class). Crustacians and shelled mollusks (especially crabs, crayfish, and scallops) compose most of the octopus diet, though octopi will also prey on fish, other cephalopods, moray eels, snails, and even sharks. Octopi have three main methods of dealing with the hard shells of their prey: using brute strength to tear a shell open (to give you a clue how strong octopi are: most humans cannot force open such shells), biting through the shell with their beak or, if these methods fail, they can drill through the shell. To drill into their prey, octopi use secretions from their salivary papillae (picture the acid spit from Sigourney Weaver type aliens) in conjunction with their radula (organic belt sander) to eat through the hard layers of their prey’s shell; they then inject a toxin which begins to digest the animal inside its shell, turning it into the octopus equivalent of a slurpee.
Giant Pacific Octopus vs Dumbass Diver
Octopi possess a multitude of strategies for escaping and avoiding predators. The first strategy for remaining safely un-eaten is to escape notice. When they are not hunting or mating, octopi stay hidden in their den; many octopi have learned to shut the entrance to their den with rocks or other materials (that's right octopuses who live in the bad part of the reef know to lock their doors at night). When an octopus does leave the safety of the den, they avoid notice with the many chromatophores in their skin. Chromatophores are what allow chameleons to change colors though octopi chromatophores change color far faster, produce a wider range of colors, and their massive brains mean their camouflage patterns are far more convincing. Octopus chromatophores and their bodies lack of any rigid shape combined mean that for all intents and purposes they are immune to visually oriented predators (predators without a strong sense of smell or crazy shark ampuelles of lorenzini probably don't even believe octopi are real and wish the other sea creatures would stop pretending "Eight arms? really? Eight arms and they have acid spit and jet skis? How gullible do you think I am?"). This active camouflage provides a double benefit because it conceals the octopus from its prey as well as its predators.
If octopi fail to avoid detection, they can fall back on the world’s most common strategy for dealing with predators: running away real fast. When threatened, most species of octopus use special ink glands to spew out a cloud of black ink, which, in addition to hiding the octopus from sight, deadens the predator’s chemoreceptors (fancy underwater nose); the octopus will then jet away from the scene (picture a motorcyclist with mace). Some octopi can also throw off pursuit by automiseing one of their limbs; this is when an octopus’s arm detaches from its body and, due to its extensive nerve chord, continues moving about to distract the predator. Since there are so many nerve bundles in them, an octopus's arm will basically keep fighting until its batteries die (octopi are like ninjas but instead of throwing smoke-bombs at people when they need to make a dramatic exit they throw limbs). If an octopus can neither distract or outrun a predator, it can often escape by squeezing its body through extremely small holes in a reef where its pursuer, which probably has a skeleton (chump), can’t follow. Rats and mice are renowned for their ability to squeeze themselves through even the tiniest of holes, imagine how much better they would be at it if they didn't even have bones. One side effect of not having any solid organs is that it renders octopi essentially invulnerable to blunt force trauma.
Blue Ringed Octopus
A few octopi have evolved an alternative method of avoiding predators by scaring them away. Octopi of the genus Hapalochlaena, once provoked, will use their chromatophores to turn their body bright yellow with blue rings which warns the threat that it is the Blue Ringed Octopus, the most toxic sea creature in the world. The Blue Ringed Octopus can spit or bite to deliver the extremely powerful paralytic neurotoxin tetrodoxin which can even be fatal to humans (it paralyzes the entire body so completely even your diaphram stops moving so you can't breath) and has no known antidote. (It’s the species from the James Bond film Octopussy). Other species of octopus that live near the Blue Ringed Octopus have learned to fake the blue rings (that's right there are octopus "posers.")
The Indonesian Mimic Octopus (Thaumoctopus mimicus) scares off predators by contorting its body and tentacles to mimic the physical likeness and movement patterns of dangerous species like lionfish and seasnakes (mime as a defensive strategy).
Indonesian Mimic Octopus (Thaumoctopus mimicus)
The average octopus life span is two years with some of the larger species living up to five years. This greatly limits the impact of their astonishing intelligence because it takes at least six years to invent firearms and the internal combustion engine. At the end of their lives octopi mate. During mating the male inserts spermatophores (sperm packets) into the female’s mantle cavity using its hectocotylus, one of its arms (usually its third arm on the right side) which is specialized for mating. The male dies soon after mating and the female dies after the hundreds of thousands (octopus reproduction greatly favors the quantity over quality school of evolution) of eggs she has laid and tended hatch. Not much is known about the first period of the octopus’s life which is spent in clouds of plankton.
A final interesting octopus factoid is that in English there are four grammatically correct ways to pluralize the word octopus: octopuses, octopi, octopede, and octopus (like sheep singular and plural=same spelling)