What is an octopus?
An octopus (plural: octopi or octopuses) is a soft-bodied animal with eight limbs. They belong to the order Octopoda which consists of about 300 octopus species. The true octopi belong to the genus octopus. Octopuses belong to the class Cephalopoda which is the same class with squids, nautiloids, and cuttlefish. They feed mainly on lobsters and crabs. Some octopuses, however, are plankton feeders. Moreso, a lot of marine fishes feed on them and for a long time now, they have also been considered a culinary delicacy by peoples of East Asia, the Mediterranean, and other parts of the world.
As a cephalopod, the octopus is bilaterally symmetric with two large complex eyes. It has a beaked mouth at the middle point of its eight limbs. Their body is saccular with a head that is slightly demarcated from the body. An octopus’s mouth possesses a pair of sharp horny beaks as well as a file-like organ called the radula. The radula is used for drilling shells and rasping away flesh. Each arm of this cephalopod has two rows of fleshy suckers. This makes them capable of great gripping power. The eight arms, however, are joined at the base by a web of tissue. This web of tissue is called the skirt, which joins the arms at the center. The mouth of octopuses lies at this center.
Octopuses have soft bodies which enable them to alter their body shape to be able to squeeze into small spaces. However, they vary in size. The smallest octopus which happens to be O. arborescens is about 2 inches (5cm) long. Whereas, the largest octopus species is about 18 feet (5.4 meters) with arms almost as long as 30 feet (9 meters).
As an octopus move, it trails the eight limbs behind it. Octopuses move by jet propulsion and are one of the most intelligent invertebrates. They have a nervous system that is complex and they use siphon for respiration. Water is taken into the octopus mantle and after respiration, the water is expelled out through the siphon. Their sense of sight is excellent and they live in various regions of the oceans. They can be found in pelagic waters, coral reefs, and even sea beds. Some inhabit the intertidal zones and some stay at abyssal depths.
The majority of octopuses mature and grow early. However, most of their lifespan is short. During reproduction in most species, the male uses an arm called a hectocotylus that is specially adapted to transfer spermatophores (packets of sperms) into the female. Octopuses, however, have separate sexes. Thus, the sperm is directly delivered into the buccal cavity of the female. After the transfer of sperm by the male, the male becomes senescent and dies. The female octopus then deposits her fertilized eggs in a den. Until these eggs hatches, they are cared for by the female and after catering for the eggs, the female octopuses die as well. This is why octopuses are short-lived.
The common octopus, for instance, mates during the winter. Hence, the eggs are laid under rocks or in holes. The eggs can amount to a total number that is more than 100,000. It takes about four to eight weeks for the larvae to hatch. During this period the female guards the eggs and cleans them with her suckers. Also, she agitates them with water. As these eggs hatch, these baby octopuses called larvae spend some time drifting in plankton. They do this for several weeks before taking refuge on the bottom. These little octopuses usually resemble their parents.
Generally, octopuses have a defense mechanism against predators. They make use of the expulsion of ink. In danger, octopuses can eject an inky substance that is used as a screen. This inky substance paralyzes the sensory organs of the predator. Also, they can camouflage and jet through the water quickly in order to hide. A lot of octopuses move by crawling along the bottom. They crawl with their arms and suckers. However, when alarmed, they shoot backward swiftly. This is done by ejecting a jet of water from the siphon. These invertebrates are venomous. However, the only species that is known to be deadly to humans is the blue-ringed octopus.
The common octopus (O. vulgaris) is the best-known octopus. It is medium-sized and is widely distributed globally in tropical and temperate seas. This species inhabits crevices or holes that are found along the rocky bottom. However, it is secretive and retiring by nature. It preys mainly on crustaceans and crabs. This particular species is said to be the most intelligent of all invertebrate animals. The common octopus has highly developed pigment-bearing cells. Thus, it can change its skin colors to an astonishing degree with great rapidity. However, each pigment-bearing cell (chromatophore) is supplied with nerves individually from the brain. Also, the veined octopus (Amphioctopus marginatus) is known for its intelligence. In 2009, this species was reported by biologists to be seen excavating half-shells of coconut from the ocean floor to use as portable shelters. Biologists regarded such behavior as the first documented example of tool use by an invertebrate.
Generally, octopuses live in the ocean- virtually every ocean. However, different species have been adapted to various marine habitats. As juveniles, the common octopus lives in shallow tide pools. On coral reefs, the Hawaiian day octopus (O. cyanea) can be seen. Also, argonauts inhabit pelagic waters whereas, Abdopus aculeatus lives in near-shore seagrass beds.
Moreso, some species are adapted to the cold oceanic depths. Take the spoon-armed octopus (Bathypolypus arcticus) for instance that is seen at depths of 3,300 ft (1,000 m). also the Vulcanoctopus hydrothermalis stays near hydrothermal vents at 6,600 ft (2,000 m). In addition, the cirrate species are usually free-swimming and live in deep-water habitats.
Furthermore, several species are known to live at bathyal and abyssal depths, even though there is only a single record of an octopus in the hadal zone. This is Grimpoteuthis (dumbo octopus). This species was photographed at 22,825 ft (6,957 m). Lastly, no octopus species are known to inhabit freshwater.
How big are octopuses?
O. wolfi, is the smallest octopus species that weighs less than 1 g and is around 1 inch (2.5 cm). The largest known octopus species is the giant Pacific octopus (Enteroctopus dofleini). The adults of this species usually weigh about 15 kg with an arm span of up to 14 feet.
However, the largest specimen of this species that is scientifically documented was one with a mass of 71 kg. Furthermore, sizes much larger than that have been claimed for the giant Pacific octopus. One was recorded as 272 kg with an arm span of 30 feet. The carcass of a seven-arm octopus, Haliphron atlanticus, weighed about 61 kg. It was estimated to have had a live mass of 75 kg.
What does an octopus look like?
An octopus is bilaterally symmetrical along its dorsoventral axis. Thus, the head and foot of octopuses are at one end of an elongated body. This serves as the anterior (front) part of octopuses. Its head contains the mouth and brain. Their body is saccular with a head that is slightly demarcated from the body.
At the top of the head are the eyes of an octopus. They are large and are structurally similar to those of a fish. The eyes are enclosed in a cartilaginous capsule which is fused to the cranium. From a translucent epidermal layer, the cornea is formed. The pupil is slit-shaped and forms a hole in the iris behind the cornea. Their lens is suspended behind the pupil and the back of the eyes are covered by photoreceptive retinal cells. Furthermore, the pupil of the eyes can be adjusted in size. There is a retinal pigment that screens incident light in bright conditions.
The foot of this animal, however, evolved into a set of flexible prehensile appendages. These appendages are known as the arms of octopuses. The arms surround the mouth of octopodes. These arms are attached to each other near their base by a webbed structure of tissues. This web of tissue is called the skirt, which joins the arms at the center. The arms of an octopus can be described depending on the arm’s side and sequence position. A description such as L1, R1, L2, R2.
However, they are divided into four pairs. The two rear arms are used to walk on the seafloor. Whereas, the other six arms are used to hunt for food. Each arm of the octopus has two rows of fleshy suckers. These make them capable of great gripping power. The eight arms however are joined at the base by a web of tissue. Octopi lack skeletal support, thus the arms work as muscular hydrostats. They contain longitudinal, transverse, and circular muscles around a central axial nerve. Hence, they have the ability to extend and contract. They can twist to the left or right, bending anywhere in any direction. Also, they can be held rigid.
Furthermore, there are circular adhesive suckers at the interior surfaces of the arms. These suckers enable the octopi to manipulate objects or anchor themselves. Each of the suckers is usually circular having two distinct parts: the outer shallow cavity which is called an infundibulum and a central hollow cavity known as an acetabulum. These two parts are thick muscles that are covered in a protective chitinous cuticle. However, when the sucker of an octopus attaches to a surface, the orifice between the two structures is sealed. The infundibulum of the sucker provides adhesion whereas, the acetabulum stays free. However, the muscle contractions of the sucker allow attachment and detachment. Moreso, each of the eight appendages can sense and respond to light. Thus, the octopi can control its limbs even if its head is concealed.
There is a bulbous and hollow mantle that is fused to the back of the octopus head. This mantle is called the visceral hump which contains the majority of the vital organs. The mantle cavity is connected to the exterior by a siphon or funnel. It has muscular walls and contains the gills of the octopus. The octopi mouth has a sharp hard beak and is located underneath the appendages. Octopi’s mouth possesses a pair of sharp horny beaks as well as a file-like organ called the radula. The radula is used for drilling shells and rasping away flesh.
An octopus skin has a thin outer epidermis with sensory cells and mucous cells. It has a connective tissue dermis that consists mainly of collagen fibers and various cells. This permits color change. Most part of an octopus body consists of soft tissue. This allows an octopus to lengthen, contract, and contort itself. Thus, it can squeeze through tiny spaces.
Even the larger species can squeeze through an opening that is close to 1 in (2.5 cm) in diameter. However, some octopus species differ in body form from the typical body form of an octopus. The cirrina, as basal species have stout gelatinous bodies. Webbing on their bodies reaches near the tip of their arms with two large fins above their eyes. Their eyes are more developed and the fleshy papillae are seen along the arms’ bottom. The bodies of the cirrina are supported by an internal shell.
How octopus moves
Generally, octopuses move by slow crawling. Some of them swim in a head-first position. However, their fastest means of movement are jet propulsion or backward swimming, followed by swimming and crawling.
Octopi will crawl on surfaces when they are not in a hurry. Several of their arms will extend forward with some of the suckers adhering to the substrate. Then, the animal with its strong-arm muscles drags itself forwards. Whereas, its other arms may push instead of pull. The other arms move ahead to repeat these actions as progress is made and the initial suckers detach.
As octopuses crawl, their heart rate nearly doubles. Thus, they require 10 or 15 minutes to recover from relatively minor exercise. However, the majority of octopuses swim by expelling a jet of water from the mantle into the sea through the siphon.
In the physical mechanism of jet propulsion, the force that is needed to accelerate the water through the orifice forms a reaction that pushes the animal in the opposite direction. However, the direction of travel is based on the orientation of the siphon.
When an octopus swims, the head is at the front and the siphon is pointed backward. Whereas, when the octopus is jetting, the visceral hump leads. The siphon is pointed towards the head of the octopus and the arms trail behind. This gives the animal a fusiform appearance presentation.
Furthermore, some octopus species in an alternative method of swimming flatten themselves dorso-ventrally. They swim with their arms held out sideways. This perhaps provides lift to the octopus and is faster than normal swimming. Octopuses use jetting to escape from danger even though it is physiologically inefficient. This is because it requires a mantle pressure that is so high to stop the heart from beating. Thus, resulting in a progressive oxygen deficit.
Also, Cirrate octopuses depend on their fins for swimming because they cannot produce jet propulsion. With their fins extended, they drift through the water and have neutral buoyancy. These octopuses can also contract their arms and the web surrounding the arms in order to make sudden moves called take-offs.
Another form of locomotion used by octopi is pumping. This involves symmetrical contractions of muscles in their webs which produces peristaltic waves that move the octopus body slowly. In 2005, certain octopuses were seen walking on two arms as they mimic plant matter. An example is the Adopus aculeatus and veined octopus (Amphioctopus marginatus). This type of movement enables them to disguise themselves and quickly run away from potential predators. However, some octopuses species can crawl out of the water briefly between tide pools. The veined octopus uses stilt walking when carrying stacked coconut shells. In stilt walking, the octopus carries the shells underneath it with two arms and moves with an awkward gait supported by its remaining arms held rigidly.
The majority of octopuses are predatory. The bottom-dwelling octopuses feed mainly on whelks, clams, crustaceans, polychaete worms, and other mollusks. Animals such as the prawns, fish, and other cephalopods are preyed upon by open-ocean octopuses. The diet of an octopus species like the giant Pacific octopus consists mainly of the cockle Clinocardium nuttallii, clams, scallops, crabs, and spider crabs.
Octopuses are likely not to eat the moon snails because they are too large. Also, they avoid eating rock scallops, limpets, chitons, and abalone. This is because these animals are too securely fixed to the rock.
Octopuses that are benthic usually move among the rocks and through the crevices. When they sight a prey, they may make a jet-propelled pounce on it. Then, with its arm and the sucker restraining it, the octopus pulls the prey towards the mouth. However, a prey that is small may be trapped completely by the webbed structure.
With paralyzing saliva, octopuses inject crustaceans like crabs and then dismember them with their beaks. They feed on shelled mollusks either by making a hole in the shell to inject a nerve toxin or by forcing the valves apart. Initially, it was assumed that the hole in the shell was drilled by the radula. However, research has shown that the minute teeth at the tip of the salivary papilla are involved. Plus, an enzyme in the toxic saliva is used to dissolve the calcium carbonate of the shell.
However, once the shell of the prey is penetrated, it dies almost immediately. The muscles of the prey relax, thus, making the tissues soft and easy for the octopus to remove. Crabs also may be treated in the same manner. The crab species that are tough-shelled are more likely to be drilled whereas, the soft-shelled species are torn apart.
There are other modes of feeding some octopus species employ. Grimpoteuthis, for instance, has a reduced or non-existent radula. Hence, it swallows its prey as a whole. There are some of the muscle cells that control the suckers in most octopuses species. However, in the deep-sea genus Stauroteuthis, these muscle cells have been replaced with photophores. These photophores are believed to fool prey by directing them towards the mouth of the animal. This mode of feeding makes these octopus species one of the few bioluminescent octopuses.
Respiration in octopus
The process of respiration in octopuses involves the following:
- Water is drawn into the mantle cavity through an aperture
- Passing the water through the gills
- Expelling the water through the siphon
The entry of water is carried out by the contraction of radial muscles in the mantle wall. When strong circular muscles expel the water out through the siphon, the flapper valves are shut. There are connective tissue lattices that render support to the respiratory muscles. They allow the respiratory muscles to expand the respiratory chamber.
The gills of this animal have a lamella structure that allows high oxygen uptake, that is up to 65% in water at 20 °C. However, the flow of water over the gills correlates with locomotion. This is because when an octopus expels water out of its siphon, it can propel its body. The thin skin of the octopus has a role to play in the process of respiration as it absorbs additional oxygen.
However, when octopuses are resting, about 41% of their oxygen absorption is through their skin. Then when it swims, the oxygen absorption decreases to 33% as more water flows over the gills. However, the skin oxygen uptake increases also. When octopi rest after a meal, the oxygen absorption through the skin can drop to 3% of their total oxygen uptake.
The number of brains the octopi possesses has been an intriguing and amazing fact. Octopuses possess a total number of 9 brains. One may wonder what the 9 brains are for. Here is an explanation.
They have a central brain and 8 others. The other 8 brains are mini-brains that each of the 8 arms of the animal possesses. These mini-brains enable each arm to act independently. Octopuses are said to be intelligent most especially because they like to play and use tools. Their central brain has a doughnut shape and forms a ring around the esophagus. Thus, as the animal swallows its food, it passes through its brain. Weird right?
The weirdest yet the interesting fact is that each arm of an octopus has a mini-brain. This sums up a lot of distributed brainpower. However, the central brain sends higher-level signals to the arms as they each have a mini-brain. For humans and other animals, usually, the brain controls each movement of our arm. Well, with these octopuses it is different. The arms act almost independently as it moves to probe into the crevice. It can taste and feel with its suckers.
Therefore, the mini-brains take a huge load off the central brain. Each arm of an octopus is controlled by a nervous system. The nervous system in the arm consists of more than 40 million neurons. These neurons are connected to the suckers of the octopus. There are about 180 million neurons in the central brain of these octopuses. The neuron in the central brain is connected to more than 40 million neurons present in each of the eight arms.
The nervous system of the octopus
Let’s discuss how the brain works with other senses of the octopus as well as the nervous system.
Octopuses and cuttlefish happen to have the highest brain-to-body mass ratios of all invertebrates. Also, it is greater than the brain-to-body mass ratios of many vertebrates.
However, the nervous system of an octopus is highly complex. It is localized in its brain which is contained in a cartilaginous capsule. The nerve cords of the octopus arms contain two-thirds of its neurons. Thus, they are capable of complex reflex actions that do not need input from the brain. Very different from vertebrates, the octopus complex motor skills are not organized in its brain.
As a cephalopod, an octopus has camera-like eyes. Thus, it can distinguish the polarization of light. Although, color vision seems to vary from species to species. for instance, Octopus aegina exhibits color vision but this is absent in Octopus vulgaris.
The opsins in the skin of this animal respond to different wavelengths of light. This helps them to choose a coloration that camouflages them. Also, the chromatophores in their skin can respond to light independently of the eyes. However, there is an alternate hypothesis. This hypothesis says that the eyes of cephalopod that has a single photoreceptor protein may use chromatic aberration to turn monochromatic vision into color vision. Though this sacrifices the quality of the image. This feature would explain pupils of the eye that are shaped like the letter U, dumbbell, or the letter W. It also explains the need for colorful mating displays.
There are two organs that are attached to the brain of the octopus. These two organs are called statocysts. They are sac-like structures that contain a mineralized mass as well as sensitive hairs. Statocysts allow octopuses to sense the orientation of their body. They give information on the position of the body in relation to gravity. Also, they can detect angular acceleration. There is an autonomic response that keeps the eyes of the octopus oriented for the pupil to be horizontal always. Also, the statocyst can be used by octopuses to hear sound. An example is a Common octopus that can hear sounds ranging from 400 Hz to 1000 Hz. It actually hears best at 600 Hz.
Aside from the sense of hearing, octopuses are said to have an exceptional sense of touch. Why is it so? The fact is that the suction cups of octopuses are equipped with chemoreceptors. This enables these octopuses to taste what they touch. Ever wondered why the arms of an octopus never tangle? The reason the arms of octopuses do not get tangled or stuck to each other is that the sensors recognize the octopus skin and prevent self-attachment. One can see how the excellent sense of touch of an octopus plays a role in its arm not getting stuck to each other.
The octopus arms have tension sensors so the octopus knows when its arms are stretched out. Though this is not sufficient enough for the brain to be able to determine the position of the octopus’s arms or body. Due to this, the octopus does not have stereognosis. This means it does not form a mental picture of the overall shape of the object it is handling. However, it can detect local texture variations but is not able to integrate the information into a larger picture. The neurological autonomy of the arms means an octopus has serious difficulty knowing about the detailed effects of its motions. Thus, it possesses a poor proprioceptive sense. It can only know what exact motions were made by visually observing its arms.
The circulatory system of the octopus is a closed one where the blood remains inside blood vessels. An octopus has three hearts. One of the hearts is a systemic heart that circulates blood around the body. The other two hearts are branchial hearts that pump blood through each of the two gills.
However, when an octopus is swimming, the systemic heart is inactive. This is why the octopus gets tired quickly and prefers to crawl. However, the systemic heart has muscular contractile walls. It has a single ventricle and two atria. Basically, one atrium for each side of the body.
The blood vessels comprise veins, arteries, and capillaries. It is lined with a cellular endothelium and this is quite different from most other invertebrates. The blood of an octopus circulates to the vena cavae through the aorta and capillary system. Then, the blood is pumped through the gills by the branchial hearts (auxiliary hearts) and then back to the main heart. Most of the venous system is contractile. Thus, helps to circulate the blood. Conclusively, the three hearts of an octopus have slightly different roles. One of the hearts circulates blood around the body, whereas the other two hearts pump blood through the gills to pick up oxygen.
The blood (hemolymph) of an octopus contains a copper-rich protein called hemocyanin. This copper-based protein, however, is more efficient at transporting oxygen molecules in cold areas with low-oxygen conditions. Hence, it is actually ideal for life in the ocean. The hemocyanin makes the octopus blood very viscous. More so, it requires considerable pressure to pump it around the body. Therefore, the blood pressure of octopuses can exceed 75 mmHg.
In comparison with hemoglobin, hemocyanin transports oxygen better in cold conditions with low oxygen levels than hemoglobin. Instead of being carried within blood cells, the hemocyanin is dissolved in the plasma. This gives the blood of an octopus a bluish color. Thus, the reason why the blood of an octopus is blue is that the hemocyanin that carries oxygen around the octopus’s body contains copper instead of iron. Copper is contrary to the iron that humans have in their hemoglobin. However, if the blood of an octopus becomes deoxygenated, the blue color fades out and the blood turns clear in color instead. An example is when the octopus dies.
All cephalopods including octopuses have flexible limbs that extend from their heads and surround their beaks. These limbs serving as muscular hydrostats are variously called arms, tentacles, or legs. However, terming these limbs, “arms” or “legs” is way acceptable than calling them “tentacles”.
Why call them ‘arms’ instead of tentacles?
The reason is that though, the terms “arm” and “tentacles” are used interchangeably. The arm of a cephalopod is often treated as distinct from a tentacle in scientific literature.
Is there a difference between arms and tentacles? Yes, there is. In contrast with tentacles, arms generally have suckers along most of their length, whereas tentacles have suckers only near their ends.
In reference to this, it is acceptable to say that octopuses have eight arms and no tentacles, whereas squid and cuttlefish have eight arms (or 2 legs, 6 arms) and two tentacles. Then, the limbs of nautiluses, which are about 90 lack suckers altogether. Hence, the limbs of nautiluses are all tentacles.
However, the set of flexible appendages of an octopus are known as the arms of an octopus. The arms surround the mouth of the octopus. These arms are attached to each other near their base by a webbed structure of tissues called the skirt. The arms of an octopus can be described depending on the arm’s side and sequence position. A description such as L1, R1, L2, R2.
However, these arms are divided into 4 pairs. The 2 rear arms are used to walk on the seafloor. Whereas, the other six arms are used to search for food. Each arm of the octopus has two rows of fleshy suckers. These make them capable of great gripping power.
An octopus lack skeletal support, thus the arms work as muscular hydrostats. They contain longitudinal, transverse, and circular muscles around a central axial nerve. Hence, they have the ability to extend and contract. They can twist to the left or right, bending anywhere in any direction. Also, they can be held rigid.
Furthermore, there are circular adhesive suckers at the interior surfaces of the arms. These suckers enable an octopus to manipulate objects or anchor itself. Each of the suckers is usually circular having two distinct parts: the outer shallow cavity which is called an infundibulum and a central hollow cavity known as an acetabulum.
These two parts are thick muscles that are covered in a protective chitinous cuticle. However, when the sucker of an octopus attaches to a surface, the orifice between the two structures is sealed. The infundibulum of the sucker provides adhesion whereas, the acetabulum stays free. However, the muscle contractions of the sucker allow attachment and detachment. Moreso, each of the eight appendages can sense and respond to light. Thus, the octopus can control its limbs even if its head is concealed.
However, there are some limb abnormalities. Several octopus arm anomalies have been recorded. Here are some examples:
- 6-armed octopus nicknamed Henry the Hexapus
- 7-armed octopus
- 10-armed Octopus briareus
- An octopus with a forked arm tip
- Octopuses with double or bilateral hectocotylization
- Octopus with up to 96 arm branches
As stated earlier, octopuses are highly intelligent. Scientists have discovered that octopuses have the ability to navigate their way through mazes. Also, they have been seen to be able to solve problems quickly and remember those solutions, at least for the short term.
Moreso, what contribution learning makes to adult octopus behavior is not known precisely. The young octopuses are not able to learn from their parents. This is because the adults render no parental care beyond tending to the eggs until the young octopuses hatch.
Octopuses, however, in laboratory experiments can readily be trained to distinguish between different patterns and shapes. From reports, they have been seen practicing observational learning. Though the authenticity of these findings is contested.
Also, octopuses have been observed in what has been described as play. They have been seen in their aquarium releasing bottles or toys repeatedly into a circular current and then catching them. Most times, they break out of their aquariums and at times into others in search of food. An example of tool use is seen in the veined octopus that collects discarded coconut shells and uses them to build a shelter.
Animal behavior associated with octopuses
Most octopus species are solitary when they are not mating. However, a few of them are known to occur in high densities. Also, with frequent interactions, mate defending, signaling, and eviction of individuals from dens. This is probably due to the abundant food supplies as well as limited den sites. The octopus species- the pacific striped octopus has been explained to be particularly social. They live in groups that are made up of up to 40 octopuses.
An octopus hides in dens. These are usually crevices in rocky outcrops or other hard structures. However, some octopus species burrow into mud or sand. Octopuses may not be territorial but they like to remain in a home range. In search of food, they may leave the area and navigate back to the den. They comfortably do this without having to retrace their outward route. They are not migratory.
Octopuses have a habit of bringing their captured prey to the den. They can safely feed on it in the den. Sometimes, the octopus may catch more than enough prey. When the prey is more than it can eat, the den is usually surrounded by a midden of the uneaten prey. Octopuses share their den with other creatures such as fish, echinoderms, crabs, and mollusks. Usually, it is either because these creatures arrived as scavengers or survived capture. Octopuses, however, on rare occasions hunt cooperatively with other species. They partner with fish. An octopus can regulate the species composition of the hunting group as well as the behavior of its partners. They do this by punching their partners.
Reproduction of octopus
An octopus has a single posteriorly located gonad. They are gonochoric. The testis in the male octopus bulges into the gonocoel. Same with the ovary in females. However, the gametes are released in the gonocoel. This gonocoel is connected to the mantle cavity by the gonoduct. It enters the mantle cavity at the gonopore.
Octopuses possess an optic gland that creates hormones that causes them to mature and age. This gland also stimulates gamete production. However, environmental conditions such as light, temperature, and nutrition can trigger the gland. Thus, these environmental conditions control the lifespan of octopuses as well as the timing of reproduction.
During reproduction, the male octopus uses a specialized arm called a hectocotylus. It uses this arm to transfer spermatophores into the female’s mantle cavity. The packet of sperms is thereby transferred from the male’s terminal organ of the reproductive tract (the cephalopod penis). The third right arm is usually the hectocotylus in benthic octopuses. It has a spoon-shaped depression with modified suckers near the tip. Fertilization occurs in the mantle cavity of most octopus species.
How octopuses reproduce has been studied in only a few species like the giant Pacific octopus. In this octopus species, courtship is accompanied by changes in skin texture and color, most especially in the male. The male octopus may cling to the top or side of the female. Alternatively, he may position himself beside her.
However, there are some assumptions that the male octopus may first use his hectocotylus to get rid of any spermatophore or sperm that is already present in the female. From his spermatophoric sac, the male octopus picks up a spermatophore with the hectocotylus. Then, he inserts the sperm into the female’s mantle cavity depositing it in the right location for the species. In the giant pacific octopus, the correct position is the opening of the oviduct. In this manner, two spermatophores are transferred. They are about one meter long with the empty ends protruding from the mantle cavity of the female. The sperm is released from the spermatophore by a complex hydraulic mechanism. The spermatophore is then stored internally by the female.
Approximately about forty days after mating, the female giant Pacific octopus attaches strings of small fertilized eggs to rocks in a crevice. Also, the eggs can be attached under an overhang. The fertilized eggs may be a total number that ranges from 10,000 to 70,000. The female octopus then guards and caters to the eggs for about five months until they hatch. However, in colder waters, like those off of Alaska, the time it takes to hatch may take longer. It may take as long as 10 months for the eggs to completely develop in such waters.
Female octopuses keep the eggs clean and aerate them. The fact is, if these eggs are left untended, many of them will not hatch. During this time, she does not feed and dies soon afterward. Also few weeks after mating, the male octopuses become senescent and dies.
These eggs have large yolks. Cleavage (division) is superficial. At the pole, a germinal disc develops. The margins of this grow down and surround the yolk during gastrulation. Thus, forming a yolk sac that eventually forms part of the octopus’ gut. Forming the embryo, the dorsal side of the disc grows upwards. The embryo develops with a shell gland on its dorsal surface, gills, mantle, and eyes. On the ventral side of the disc, the arms and funnel develop as part of the foot. These arms later migrate upwards to form a ring around the funnel and mouth. As the embryo forms, the yolk is gradually absorbed.
Furthermore, the majority of the young octopuses hatch as paralarvae. Depending on the octopus species and the temperature of the water, these young octopuses are planktonic for weeks to months. They feed on arthropod larvae, copepods, and other zooplankton. Eventually, with time, they settle on the ocean floor and develop directly into adults. They develop with no distinct metamorphoses that are present in other groups of mollusk larvae.
There are octopus species that produce larger eggs. Such species do not have a paralarvae stage. Rather, they hatch as benthic animals. Thus similar to the adults. Such octopus species include the deep-sea octopuses, California two-spot octopuses, southern blue-ringed octopus, Caribbean reef octopus, and Eledone moschata. The female in the argonaut (paper nautilus) secretes a fine fluted and papery shell. Her eggs are deposited in this shell and she also resides in it while floating in mid-ocean. She broods the young in it, and it serves also as a buoyancy aid as it allows her to adjust her depth. The male Argonaut, however, is minute compared to the female and has no shell.
The life expectancy of Octopuses is relatively short. Some octopus species live for as short as six months. However, the giant Pacific octopus, which is one of the largest octopus species, may live for as long as 5 years.
In octopuses, reproduction limits their lifespan. The male octopuses may live for only a few months after mating, whereas the female octopuses may die shortly after their eggs hatch. An exception, however, is the larger Pacific striped octopus. This octopus species can reproduce multiple times over a life of around two years.
The reproductive organs of an octopus mature as a result of the hormonal influence of the optic gland. This leads to the inactivation of their digestive glands which eventually cause octopuses to die from starvation. Moreso, the experimental removal of both optic glands after spawning was seen to cause the following:
- Cessation of broodiness
- Resumption of feeding
- Increased growth
- Extended lifespans
Conclusively, it has been proposed that the natural short lifespan of octopuses may be functional to checkmate rapid overpopulation.
Defense and camouflage
Octopuses are preyed on by humans, cetaceans, fishes, seabirds, sea otters, pinnipeds, and other cephalopods. Due to predation, they hide or disguise themselves using camouflage and mimicry. Some octopuses have conspicuous warning coloration (aposematism) or deimatic behavior. Also, when octopuses hunt, they use camouflage to avoid predators. For them to be able to camouflage, they make use of specialized skin cells.
These skin cells change the appearance of the skin by adjusting its opacity, color, or reflectivity. They have developed pigment-bearing cells that can change the color of the skin. However, these pigment-bearing cells (chromatophores) contain yellow, red, orange, brown, or black pigments. The majority of octopus species possess 3 of these colors, whereas some have 2 or 4. Also, reflective iridophores and white leucophores are other color-changing cells. This color-changing or camouflage ability is also used amongst octopuses to communicate with one another or warn other octopuses.
Octopuses exhibit a display known as “passing cloud”. This is a behavior where they create distracting patterns with waves of dark coloration across their body. The muscles in the skin change the mantle texture in order to form greater camouflage. However, in some octopus species, the mantle can adopt the spiky appearance of algae. The skin anatomy in other octopus species is limited to relatively uniform shades of one color and limited skin texture.
Octopuses that are diurnal and live in shallow water have complex skin. They have evolved more complex skin than octopuses that are nocturnal and deep-sea. Some octopuses are able to exhibit the “moving rock” trick. This trick involves them mimicking a rock and inching across the open space with a speed that matches the surrounding water.
Octopuses may spend 40% of their time hiding away in their den. However, when it is approached, it may extend an arm to investigate. In a study, about 66% of Enteroctopus dofleini had scars with about 50% of them having amputated arms. There are blue rings hidden in the muscular skin folds of the highly venomous blue-ringed octopus. When this animal is threatened, these muscular skin folds contract, thus, exposing the iridescent warning.
Another defense mechanism is seen in the Atlantic white-spotted octopus (Callistoctopus macropus). This octopus turns bright brownish red with oval white spots all over. The coloration is in a high contrast display. It usually reinforces this display by stretching out its arms, fins, or web to make it look as big and threatening as possible.
Also, arm autonomy is another defense mechanism that octopuses employ. When they are under attack, some of them can perform arm autotomy. This is done similarly to the manner in which skinks and other lizards detach their tails. The detached crawling arm may distract the potential predators. Interestingly, the severed or detached arms of the octopus remain sensitive to stimuli and move away from unpleasant sensations. After carrying out arm autonomy, these octopuses can replace the lost arms (limbs).
Mimicry is another defense mechanism employed by octopuses. Some octopuses can mimic other animals that are more dangerous. A typical example of such octopus species is the mimic octopus. These octopuses can combine their very flexible bodies and their ability to change color in order to mimic other more dangerous animals. They can mimic animals such as eel, lionfish, and sea snakes.
Octopuses have an ink sac. This ink sac is found under the digestive gland. There is a gland attached to the sac that produces the ink which the sac stores. This ink sac is close enough to the siphon (or funnel) so that with a water jet, the octopus can shoot out the ink. However, before the ink leaves the funnel, it passes through glands. These glands mix it with mucus forming a thick dark blob that allows them to escape from their predator. Melanin is the main pigment in the ink which gives it its black color. Some octopus species such as the Cirrate octopuses usually lack the ink sac.
Once octopuses have been seen by a predator, they usually try to escape. They can also create a distraction with an ink cloud that is ejected from their ink sac. This ink is said to reduce the efficiency of olfactory organs. This will help escape from predators such as sharks that use smell for hunting. Moreso, the ink clouds of some octopus species might serve as distracting pseudomorphs or decoys that the predator may attack instead.
- Greater Blue-ringed Octopus (Hapalochlaena lunulata)
- Southern Blue-Ringed Octopus (Hapalochlaena maculosa)
- Giant Pacific Octopus (Enteroctopus dofleini)
- Mosaic Octopus (O. abaculus)
- Mimic octopus (Thaumoctopus mimicus)
- Algae Octopus (Abdopus aculeatus)
- Flapjack Octopus (Opisthoteuthidae californiana)
- Sandbird Octopus (Amphioctopus aegina)
- Seven-Arm Octopus (Haliphron atlanticus)
- Common octopus (O. vulgaris)
- Capricorn Octopus (Callistoctopus alphaeus)
- Dumbo Octopus (Grimpoteuthis)
- Coconut octopus (Amphioctopus marginatus)
- Hammer Octopus (O. australis)
- California two-spot octopus (O. bimaculoides)
- Southern Keeled Octopus (O. berrima)
- Common Blanket Octopus (Tremoctopus violaceus)
- East Pacific Red Octopus (O. rubescens)
- Lilliput Longarm Octopus (Macrotritopus defilippi)
- Star-sucker Pygmy Octopus (O. wolfi)
- Caribbean reef octopus (O. briareus)
- Atlantic Pygmy Octopus (O. joubini)
- Bock’s pygmy octopus (O. bocki)
- North Pacific bigeye octopus (O. californicus)
- Lesser Pacific striped octopus (O. chierchiae)
- Chestnut octopus (O. conispadiceus)
- Big blue or Cyane’s octopus (O. cyanea)
- Fitch’s pygmy octopus (O. fitchi)
- Globe octopus (O. globosus)
- Hubb’s octopus (O. hubbsorum)
- Bumblebee two-spot or Caribbean two-spot octopus (O. hummelincki)
- Atlantic pygmy or small-egg Caribbean pygmy octopus (O. joubini)
- Mexican four-eyed octopus (O. maya)
- California Lilliput octopus (O. micropyrsus)
- Galapagos reef octopus (O. oculifer)
- Pale octopus (O. pallidus)
- Japanese pygmy octopus (O. parvus)
- spider octopus (O. salutii)
- Moon octopus (O. selene)
- Frilled pygmy octopus (O. superciliosus)
- Tehuelche or Patagonian octopus (O. tehuelchus)
- gloomy or common Sydney octopus (O. tetricus)
- Veiled octopus (O. veligero)
- Bighead octopus (O. vitiensis)
- Club pygmy octopus (O. warringa)
- Atlantic banded octopus (O. zonatus)
- Spoon-armed octopus (Bathypolypus arcticus)
- Southern sand octopus (O. kaurna)
- Abdopus aculeatus
- Vulcanoctopus hydrothermalis
- O. yendoi
- O. verrucosus
- O. validus
- O. alatus
- O. alecto
- O. araneoides
- O. arborescens
- O. argus
- O. balboai
- O. berenice
- O. diminutus
- O. favonius
- O. filamentosus
- O. filosus
- O. fujitai
- O. gardineri
- O. gorgonus
- O. harpedon
- O. hattai
- O. hawaiiensis
- O. hongkongensis
- O. humilis
- O. huttoni
- O. incella
- O. insularis
- O. jeraldi
- O. kaharoa
- O. kermedecensis
- O. laqueus
- O. longispadiceus
Frequently Asked Questions
How smart are octopuses?
Octopuses are very smart and intelligent. Many of them have been seen carrying tools around. This proves that they have an understanding that the tool can become useful in the future. That is a smart gesture. An example of tool use is seen in the veined octopus that collects discarded coconut shells and uses them to build a shelter.
Scientists have discovered that octopuses have the ability to navigate their way through mazes. Also, they have been seen to be able to solve problems quickly and remember those solutions, at least for the short term. Octopuses, however, in laboratory experiments can readily be trained to distinguish between different patterns and shapes. From reports, they have been seen practicing observational learning. Though the authenticity of these findings is contested.
Also, octopuses have been observed in what has been described as play. They have been seen in their aquarium releasing bottles or toys repeatedly into a circular current and then catching them. Most times, they break out of their aquariums and at times into others in search of food.
These octopuses sure behave in ways that suggest they’re smart and highly intelligent. For example, an octopus named Inky made a notorious escape from the National Aquarium of New Zealand. It broke out of its enclosure, slithering into a floor drain and out to the sea.
What do octopuses eat?
Octopuses feed mainly on lobsters and crabs. Some, however, are plankton feeders. The majority of octopuses are predatory. Bottom-dwelling octopuses feed mainly on whelks, clams, crustaceans, polychaete worms, and other mollusks. Animals such as the prawns, fish, and other cephalopods are preyed upon by open-ocean octopuses. The diet of an octopus species like the giant Pacific octopus consists mainly of the cockle Clinocardium nuttallii, clams, scallops, crabs, and spider crabs.
Furthermore, octopuses are likely to not eat the moon snails because they are too large. Also, they avoid eating limpets, rock scallops, chitons, and abalone. This is because these animals are too securely fixed to the rock.
How long does an octopus live?
Octopuses do not live for long. They are generally short-lived except for the giant pacific octopus which is an exception. The life expectancy of octopuses is relatively short. Some octopus species live for six months whereas, the giant Pacific octopus can live for as long as five years.
For octopuses, their reproduction limits their lifespan. The time duration between egg hatching, reproduction, and death varies among octopus species. For example, Octopus vulgaris may live for only 2 years. Whereas the giant octopuses can live for 3 years and even up live as long as 5 years as far as they don’t mate.
The male octopus species may live for only a few months after mating, whereas the female octopus species may die shortly after their eggs hatch. An exception, however, is the larger Pacific striped octopus. This octopus species can reproduce multiple times over a life of around 2 years.
Are octopuses dangerous?
All octopus species are venomous. They can be dangerous even though the only venom that is lethal to humans is the venom from blue-ringed octopuses. Each year there have been reports of bites across the animals’ range from Australia to the eastern Indo-Pacific Ocean.
However, octopuses only bite when they are provoked or accidentally stepped upon. An octopus bite is small and usually painless. The venom of an octopus seems to have the ability to penetrate the skin without a puncture when given prolonged contact.
An octopus venom contains tetrodotoxin. This toxin results in paralysis by blocking the transmission of nerve impulses to the muscles. Hence, causing death as a result of respiratory failure that led to cerebral anoxia.
There is no antidote known for this venom. However, a patient can recover within 24 hours if breathing can be kept stable artificially. Also, there have been recorded bites from captive octopuses of other species. The bites leave swellings that disappear in a day or two.
How many hearts does an octopus have?
An octopus has 3 hearts. These octopus hearts have slightly different roles. One of the hearts circulates blood around the body, whereas the other two hearts pump blood past the gills to pick up oxygen.
What color is an octopus blood
The color of an octopus’s blood is blue. They have blue blood because these animals have adapted to cold waters that have low oxygen levels. Thus, octopuses make use of hemocyanin, a copper-rich protein that is more efficient at transporting oxygen molecules in cold areas with low-oxygen conditions.
In comparison with hemoglobin, hemocyanin transports oxygen better in cold conditions with low oxygen levels than hemoglobin. Instead of being carried within blood cells, the hemocyanin is dissolved in the plasma. This gives the blood a bluish color, thus, the reason why the blood of octopuses is blue. The blood is blue because hemocyanin that carries oxygen around the octopus’s body, contains copper instead of iron as humans have in their hemoglobin.
How many legs do octopuses have?
Generally, octopuses have 8 limbs or arms. Most times, people prefer to refer to an octopus with 8 limbs as having 6 arms and 2 legs. In addition to over 2000 observations by visitors, teams of aquatic specialists carried out a study. It was observed that the octopus seemed to prefer using their first 3 pairs (6) of limbs for grabbing and using objects. Thus, according to a Sealife biologist, Oliver Walenciak, it can be assumed that the front six limbs function as arms for octopuses whereas, the back two limbs function as legs.
Is an octopus a fish?
Octopuses are invertebrate marine animals just like a fish but it is not a fish. They are cephalopods same as cuttlefish and squid.
They belong to the class Cephalopoda which is part of the phylum Mollusca. Thus an octopus is also a mollusk. Octopuses are mollusks and other animals under this phylum classification include gastropods such as slugs and snails, bivalves (clams and oysters), and several others.
Fishes, on the other hand, belong to a different phylum- Chordata. There is a huge difference between an octopus and a fish. For instance, fishes have scales whereas, octopuses do not. An octopus can move with jet propulsion of water, whereas fishes depend on wave-like movements of their body in order to move. Moreso, octopuses tend to be more smarter and intelligent than fishes. They can make use of tools and tend to solve problems. Fishes, on the other hand, do not show such a level of intelligence.
How many tentacles does an octopus have?
Octopuses do not have tentacles. The majority of people think of cephalopods when they hear the word “tentacles”. Cephalopods include snail, shellfish, squid, cuttlefish as well as octopuses.
All animals in this family have arms, but only cuttlefish and squid have tentacles. Tentacles are not the same thing as arms and can be distinguishable. They are retractable and longer than arms. Also, they have a flattened or spade-shaped tip. In contrast with tentacles, arms generally have suckers along most of their length, whereas tentacles have suckers only near their ends.
In reference to this, it is acceptable to say that octopuses have eight arms and no tentacles, whereas squid and cuttlefish have eight arms and two tentacles.
Do octopuses have 3 hearts?
Yes, an octopus has three hearts. One of the hearts is a systemic heart that circulates blood around the body. The other two hearts are branchial hearts that pump blood through each of the two gills.
What is the plural of octopus?
The plural of octopus, depending on which dictionary is consulted, can be written in three different ways which are octopi, octopuses, and octopodes. However, according to the Merriam-Webster dictionary, the plural forms:- octopi, octopuses, and octopodes come from the various ways the English language adopts plurals.
The plural form “Octopi” is the oldest plural which comes from the belief that there should be Latin endings for Latin origins. Next is the plural form “Octopuses” which gives the word an English ending that matches its adoption as an English word. Then, the plural form “octopodes” comes from the belief that octopus should have a greek ending because it is originally Greek.
However, the final and preferred plural option is “octopuses” when speaking and writing in English. According to Merriam-Webster, this plural form came about later in the nineteenth century and has the attached -es ending to align with the English formation of plurals.
How many brains does an octopus have?
An octopus has 9 brains: 1 central brain and 8 mini-brains. Each arm of an octopus has a mini-brain, making it 8 mini-brains altogether.
Why do octopuses have 9 brains?
Octopuses have 9 brains because the central brain sends higher-level signals to the arms as they each have a mini-brain. For humans and other animals, usually, the brain controls each movement of our arm. Well, with an octopus it is different. The arms act almost independently as it moves to probe into the crevice. It can taste and feel with its suckers. Therefore, the mini-brains takes a huge load off the central brain
How do octopuses mate?
In mating, the male octopus uses an arm called a hectocotylus that is specially adapted to transfer spermatophores (packets of sperms) into the female. Octopuses, however, have separate sexes. Thus, the sperm is directly delivered into the buccal cavity of the female.
During mating, the male octopus may cling to the top or side of the female. Alternatively, he may position himself beside her. However, there are some assumptions that the male octopus may first use his hectocotylus to get rid of any sperm that is already present in the female.
From his spermatophoric sac, the male octopus picks up a spermatophore with the hectocotylus. Then, he inserts the sperm into the female’s mantle cavity depositing it in the right location for the species. In the giant pacific octopus, the correct position is the opening of the oviduct.
In this manner, two spermatophores are transferred. The sperm is released from the spermatophore by a complex hydraulic mechanism. The spermatophore is then stored internally by the female. After the transfer of sperm by the male, the male becomes senescent and dies.
Approximately about 40 days after mating, the female deposits her fertilized eggs in a den. The fertilized eggs may be a total number that ranges from 10,000 to 70,000. The female octopus then guards and caters to the eggs for about 5 months until they hatch. However, in colder waters, like those off of Alaska, the time it takes to hatch might be longer. It may take as long as 10 months for the eggs to completely develop in such waters.
Until these eggs hatches, they are cared for by the female octopus and after catering for the eggs, the female octopuses die as well. They keep the eggs clean and aerates them. The fact is that if these eggs are left untended, many of them will not hatch. During this time, the female octopus does not feed and dies soon afterward. Also few weeks after mating, the male octopuses become senescent and dies
Why do octopuses live so short?
Octopuses live so short because reproduction limits their lifespan. The time duration between egg hatching, reproduction, and death varies among octopus species. For example, Octopus vulgaris may live for only 2 years. Whereas the giant octopuses can live for 3 years and even up live as long as 5 years as far as they don’t mate.
The reproductive organs of an octopus mature as a result of the hormonal influence of the optic gland. This leads to the inactivation of their digestive glands which eventually cause the octopus to die from starvation.
Thus, the life expectancy of octopuses is relatively short. Some octopus species live for as short as six months. However, the giant Pacific octopus, which is one of the largest octopus species, may live for as long as 5 years.