Adaptations for Survival

    The giant Pacific octopus has developed many adaptations in order for it to survive in its environment. Some of the more interesting adaptations are described below.

Arms: Like all octopuses, the Pacific octopus has eight arms. The two rear-most arms function as "legs." They are used to push off of the ocean floor, anchor itself in one place, and crawl over rocks and debris. The other six arms are used as “arms” are expected to be used. They grab objects, feel around, and feed the octopus. Every arm contains both radial and longitudinal muscles. This muscle combination makes them very strong. The arms are able to resist a pull one hundred times the octopus’s weight, which is roughly 4,000 pounds. There are no bones in the Pacific octopus's arms, or its entire body either, which allows the arms to be very flexible. This flexibility is useful and allows the octopus to fit the arms into small crevices.

Suckers: Each arm of the Pacific octopus contains about 280 suckers. The suckers play an important role in both the octopus’s sense of touch and taste. Each sucker is believed to contain thousands of chemical receptors. The rims of the suckers are a particularly sensitive area to touch. It is expected that a blindfolded octopus could differentiate objects by sense of touch as easily as the octopus could sense an object using its sense of sight. The suckers are also able to create a suction and grip onto prey or the substrate.

Hectocotylus: This is a reproductive organ found only on the male octopuses. It makes up a male's third right arm. This arm stands out because it is the only arm that does not contain the full amount of suckers. The last fifth of the arm, instead, has a ciliated crease running down the center. The terminal portion of the hectocotylus is called the ligula, which contains erectile tissue. The ligula does not have any chromatophores, however, so males frequently keep it curled up to maintain their camouflage. More details of the male's use of the hectocotylus can be found on the reproduction page.

Statocyst: The statocyst receptors are used by this octopus to detect angular rotation. They are able to use detect rotation in three planes, at right angles to each other. This way the octopus determine its body’s orientation in relation to the ocean floor. It uses hair cells, along with gravity, to complete this task. It may also use these hair cells, along with vibrations, to “hear.” Octopuses have been found to be most sensitive to lower-frequency vibrations.

Eyes: Pacific octopuses have very advanced eye structures. They contain many of the parts that human eyes do, including: the iris, the pupil, the lens, the retina, and the optic nerve. However, the pupil is not a round shape, but is a horizontal slit. When focusing, the octopus’s eye moves the lens forward and backward, instead of altering its curvature like humans. The eye is one of the most important senses to the Pacific octopus. It uses its sense of vision to choose a mate, find a den, blend in with its environment, and locate prey.

Brain: This invertebrate is a very intelligent creature and has a complete nervous system. Since it does not have many defensive adaptations, it must use its brain to survive. The intelligence of these octopuses has undergone much research. More information about it can be found here: Intelligence.

Hearts: This octopus has three hearts. They each pump blood through the octopus’s closed circulatory system. This system also includes: veins, arteries and capillaries. Two of the hearts pump blood to the two gills and the third heart pumps blood to the rest of the octopus's body. The blood also contains the important oxygen-transporting molecule, hemocyanin.

Chromatophores: Camouflage is an important method of defense used by the Pacific octopus. Chromatophores are the pigmentation sacs that allow octopuses to blend into their surroundings so flawlessly. Each chromatophore is made up of three different pigment sacs: yellow, red, and brown. The colored appearance of the octopus’s skin is determined by small muscles. These muscles will pull a colored pigment sac to the surface to make that color is visible. When the muscle relaxes, the pigmentation from that sac goes away. The octopus uses its eyes to judge the color and texture of the camouflage it wants to wear. Working in conjugation with chromatophores are papillae. These small muscles under the skin are able to form the skin into peaks of varying heights. This allows the octopus to look rough or smooth, whichever blends in best with its current environment. Finally, males innately know which skin patterns to flash at females during in the courting process of reproduction.  

Mouth: The mouth structure on the Pacific octopus contains many important feeding adaptations. A beak, which greatly resembles a parrot’s, is sharp and used to bite and grasp prey. Inside the beak is a radula. This is a very rough tongue-like structure that contains ribbons of small teeth. The radula is used to scrape up their prey, often from within the prey's own shell! Salivary glands within the octopus’s mouth region contain venom. The venom is used both to paralyze the prey and begin the octopus's digestion process. The venom is passed out through the salivary papillae. At the end of the salivary papillae is a set of drill-shaped teeth. These teeth are used to bore holes into the shells of the octopus’s prey.

Siphon: The siphon can be found near the base of the octopus’s mantle (the round-shaped head/body area.) The siphon is a primary player in the Pacific octopus's respiration. Water flows into the gill slit, goes past the gills, and is ejected out of the tube-shaped siphon.(A video of this can be seen here. With the use of quick muscular contractions, the octopus is able to rapidly shoot the water out of the siphon. This allows the octopus to zoom away, head-first, using jet propulsion. Under the octopus’s digestive gland is the ink production gland. The ink is produced here, then stored in a larger sac, which is near the siphon. On a command, usually triggered by fear, the octopus releases the ink. Before being squirted out, the ink mixes with mucus. The ink solution is then expelled out of the siphon's opening. This causes the allows the octopus to use jet propulsion and flee in the opposite direction since the attacker is unable to see through the ink. 

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A method of controling the osmolarity of their bodies

One of the big challenges in moving on land is dealing with osmotic balance (how salty the internal environment of the cells in the body is). Most organisms have internal cell contents that are quite salty, but maintaining a consistent salinity level is necessary for survival and proper metabolism.

A lot of terrestrial organisms are thought to have moved into fresh or brackish water before moving onto land, and even if you do go straight from marine waters to land if you want to go inland you have to deal with every reliable source of water potentially being too dangerous to drink. Saltwater animals retain freshwater and excrete high amounts of salts. Freshwater animals absorb salt through their gills and excrete a lot of water. It is possible to do both, but you have to be able to regulate your internal salinity and it is hard (as evidenced by the rarity of salt-and-freshwater tolerant fish rather than just salt or just freshwater).

Most cephalopod species are osmoconformers, and are stenohaline, which means they mostly keep their body salinity at the same level as the surrounding saltwater and really don't like it when the salinity changes. Kind of like sharks to some degree. A giant squid or a Humboldt squid could get large enough to simply ignore salinity changes for short periods of time due to osmological inertia, but large cephalopods generally don't live close to estuaries. A Pacific giant octopus might be able to handle it, and there are apparently reports of this happening, but given that is self-reported on the internet I would take it with a grain of salt.

The first step to putting a cephalopod on land would be to give them a system of osmoregulation they can use to tolerate the more osmologically varied environements of tide pools, estuaries, and rivers. This isn't impossible probably, fishes have done it and at least two other groups of mollusks have colonized freshwatr (clams and gastropods), and notably gastropods then went on to colonize land (though I'm not sure how well they osmoregulate given the whole salt thing). Notably, there are no freshwater cephalopods and as far as we know there never have been in the fossil record, though a couple of species tolerate brackish water.