OCTOPUS: CHARACTERISTICS, HEARTS, HABITAT, REPRODUCTION, BEHAVIOR - BIOLOGY - 2025

The octopus is a mollusk that belongs to the order Octopoda. It has a body made up of soft tissues, which give it great flexibility to bend and contort. On the head it has the eyes and eight appendages, joined together around the mouth.

At the back of the head, fused to it, is the mantle, which is hollow and muscular. The vast majority of the vital organs of this species are contained within it.

Octopus. Source: Pseudopanax at English Wikipedia

The order Octopoda has two suborders, Incirrina and Cirrina. The incirrine group is distinguished from the cirrhines by the lack of cylindrical filaments (cirri) in the suction cups of the arms. In addition, they do not have the fins above the eyes, nor the net on the appendages.

Regarding distribution, the octopus is found in all oceanic waters worldwide. Some species are benthic and others live alternately between a pelagic and a benthic habitat. Likewise, various octopuses develop in medium or superficial marine waters.

A peculiarity of this animal is that it has three hearts, one systemic and two gill. In addition, your nervous system is complex, made up of a brain and two lobes.

Locomotion

The octopus moves in various ways, the choice of the mode of locomotion will depend on how fast it needs to move. In this sense, if you need to quickly escape a threat, use jet propulsion, also known as backward swimming.

For this, the muscular layers of the mantle contract, violently emptying the water that is in the cavity, thus expelling it outside through the siphon. In this way, the force propels the cephalopod in the opposite direction to the jet of water. The direction of the displacement will depend on the orientation of the siphon.

This mode of locomotion, while allowing the animal to escape danger, is physiologically inefficient. This is because the contraction of the mantle requires high pressure, preventing the systemic heart from beating, causing a progressive oxygen deficit.

When the octopus is not in a hurry, it usually crawls. Thus, it extends several appendages forward, causing some suction cups to adhere to the substrate. Then the animal moves, propelling itself with arms that are outstretched. The other arms contribute by pushing the body. In this type of displacement, the heart rate almost doubles, so the body requires some time to recover.

Movement in cirrhines

The species of the suborder Cirrina, depend on the fins to swim. Thus, they move from one place to another with their fins extended. In addition, they have the ability to contract the appendages and the network that joins them, which produces sudden movements, called takeoffs.

Another mode of locomotion is pumping. In this, the muscles of the networks contract symmetrically, producing peristaltic waves. In this way the octopus moves slowly through the marine waters.

General characteristics

Size

The range in size of the octopus varies greatly. In this sense, the giant Pacific octopus (Enteroctopus dofleini) is one of the largest species worldwide. The adult weighs approximately 15 kilograms, although there is a review of one that weighed 71 kilograms. The arm can measure four meters.

On the other hand, the common octopus (Octopus vulgaris) is smaller, growing up to 90 centimeters. However, the smallest of the order Octopoda is the Octopus wolfi, which is 2.5 cm long and weighs 1 gram.

Skin

The outer layer of octopus skin is made up of a thin epidermis, which contains sensory cells and mucous membranes. Below is the dermis, made up of connective tissue, collagen fibers and cells that have the property of varying the tone of the skin.

Chromatophores

The changes in tones that the skin of the octopus has, as part of the defense mechanisms, is due to the chromatophores. These pigmented cells, which reflect light, contain three sacs of color. Each chromatophore is linked to various muscles, which by contracting or relaxing, modify the way each pigment is presented.

The nervous system is in charge of independently controlling each chromatophore. This implies a high degree of complexity and control in the display of colors. In this way, the appearance of the octopus can change in less than a second.

Head

The mouth is located under the arms. This is characterized by having a hard and sharp beak. As for the eyes, they are large and located on the top of the head. These structures are enclosed in a cartilaginous capsule, which fuses with the skull.

In relation to the cornea, it originates from a translucent epidermal layer. The pupil is shaped like a slit and adjusts its size, contracting or dilating, to regulate the entry of light into the eye.

Appendices

The octopus has a set of prehensile and flexible appendages, which are known as arms. These surround the mouth and are joined together near the base, by means of a webbed structure.

They are divided into four pairs, the rear pair is generally used for walking on the seabed. The other 6 arms are used in the search for food.

The arms lack bone structure and are made up of transverse, longitudinal, and circular muscles, oriented around a central axial nerve. The inner surface of each appendage is covered with adhesive circular suction cups. These allow the octopus to anchor itself to a surface or to manipulate objects.

The suction cups are concave and have two parts: a shallow cavity, called the infundibulum, and a central cleft, known as the acetabulum. This is made up of thick muscles, protected by a chitinous cuticle.

When the suction cup adheres to a substrate, the infundibulum provides the adhesion, while the acetabulum can freely contract or distend. In this way, the animal is held or detached from the surface.

Mantle

The mantle is a muscular structure located at the back of the head. In this are the vast majority of vital organs. The strong muscles that form it protect the structures that are inside, in addition to contributing to the respiratory process.

In the mantle there is a tubular opening, called a siphon. From this, the water that is taken through the mouth opening is expelled. Thus, the siphon is used for respiration, waste removal and ink discharge.

Body

A large part of the body of the octopus is made up of soft tissues, which allow it to contort, lengthen or contract. Thus, the animal can pass through very small spaces, with openings up to 2.5 centimeters in diameter.

Because the arms lack skeletal support, they function as muscular hydrostatics. These can contract, extend and rotate to the right or to the left. In addition, they bend anywhere and in various directions, although they can also remain rigid.

Regarding the form, it differs according to the species. Thus, those that make up the Cirrina suborder have gelatinous bodies, with a network that extends almost to the tips of the arms. Also, they have two large fins above the eyes, organs that are much more developed than those of the suborder Incirrina.

Breathing

The respiration process involves the entry of water into the cavity of the mantle through an opening that exists in it. The liquid passes through the gills and is then expelled through the siphon.

The entry of water into the body is achieved by the contraction of the radial muscles that make up the wall of the mantle. As for the flap valves, these close at the moment that the circular muscles eliminate the water through the siphon.

Respiratory muscles are supported by connective tissue networks which facilitates the expansion of the respiratory chamber. On the other hand, the laminar structure of the gills allows a high percentage of oxygen absorption.

The flow of water in the gills is correlated with locomotion, so the octopus couples its breath to movement through the water. Thus, the animal propels its body when the water is forced out of the siphon.

On the other hand, the thin skin of the octopus absorbs oxygen. While resting, about 41% of oxygen enters the body through the skin. This percentage decreases to 33% when swimming, as more water flows through the gills.

How many hearts does an octopus have?

The octopus has three hearts. The systemic heart is the one that sends blood through the different tissues and organs of the body. The other two hearts are the ones that carry blood to the gills, to oxygenate it.

In relation to blood vessels, they are made up of capillaries, arteries and veins. These are lined by a cellular endothelium, different from the one that exists in the vast majority of invertebrate animals.

Blood is bluish in color because it contains dissolved hemocyanin, a protein rich in copper. This is a remarkable difference, in relation to vertebrates, whose blood is red, due to hemoglobin, rich in iron.

This particularity in the octopus's blood makes it viscous, which is why greater pressure is required to pump it throughout the body. Thus, blood pressure could exceed 75 mmHg. On the other hand, hemocyanin, in low temperature conditions, efficiently transports oxygen.

Blood circulation

The oxygenated blood, coming from the gills, enters the systemic heart, which is the largest of the three that the octopus possesses. From there, it goes through the main artery to the different organ systems. When it returns, loaded with carbon dioxide, it enters through the main vein, which forks into two branches, directed at each gill.

Near the base of each of the gills is a branchial heart, which sends deoxygenated blood into an afferent branchial vessel. Subsequently, the already oxygenated blood passes through the branchial capillaries, reaching the efferent branchial vessel, which carries it to the systemic heart.

Taxonomy and classification

-Animal Kingdom.

-Subreino: Bilateria.

-Superfilum: Lophozoa

-Filum: Mollusca.

-Class: Cephalopoda.

-Subclass: Coleoidea.

-Superorden: Octobrachia.

-Order: Octopoda.

Suborder: Cirrina.

-Family: Cirroteuthidae.

-Family: Stauroteuthidae.

-Family: Opisthoteuthidae.

Suborder: Incirrina.

-Family: Alloposidae.

-Family: Vitreledonellidae.

-Family: Amphitretidae.

- Family: Tremoctopodidae.

-Family: Argonautidae.

-Family: Ocythoidae.

-Family: Bolitaenidae.

-Family: Octopodidae.

-Family: Idioctopodidae.

Habitat and distribution

Octopuses are distributed in the different oceans worldwide. In general, members of the order Octopoda live in a wide variety of regions and at various depths. This peculiarity is one of the reasons why these animals have survived for millions of years.

In this sense, the common octopus (Octopus vulgaris) lives in shallow waters, with a maximum depth of 100 meters, while the Argonauta argo is a species that makes life pelagic, in subtropical and tropical waters around the world.

In the regions where it lives, the octopus creates lairs to hide in. Also, it can hide under rocks or in small crevices, which it can access thanks to the great flexibility of its body.

Octopuses are part of the cephalopod mollusks, studied by malacology

Image by edmondlafoto from Pixabay

Adaptations

Some of the species are adapted to specific marine habitats, where they have optimal conditions for their development. For example, the Hawaiian octopus (Octopus cyanea) prefers coral reefs and the Abdopus aculeatus lives almost exclusively on seagrass beds, which are close to the coast.

Other species can live in the cold depths of the ocean. Thus, the North Atlantic octopus (Bathypolypus arcticus) inhabits abyssal plains, at depths of up to 1,000 meters.

Contrary to this, Vulcanoctopus hydrothermalis is endemic to hydrothermal vents in the Eastern Pacific, where the waters are geothermally hot.

Reproduction

Considering the characteristics of each species, mating can occur from two months to one year of age. During the juvenile stage there are no external characteristics that allow differentiating the male from the female. However, when both are adults there is an evident sexual dimorphism.

Generally in the male, the third right arm undergoes modifications at its end. Thus, the hectocotyl, as this appendix is ​​called, functions as a penis.

Mating

Courtship does not exist in all species. However, in the male, this ritual usually includes changes in the color and texture of the skin. When the female accepts the male, she may lie on her side, cling laterally, or position herself on top of her mate.

Some experts affirm that the octopus, before fertilizing the female, first uses the hectocotyl to eliminate any remaining sperm that exists in her body. Then, with that same arm, she collects a spermatophore from the sac where it is stored and inserts it into the opening of the oviduct, located in the cavity of the female's mantle.

This procedure is done twice, so that both capsules, which contain the sperm, may protrude slightly from the mantle. A complex mechanism causes the release of sperm, which is stored internally by the female.

Once it produces the eggs, it looks for an area to make the laying, which can be a cave or a hidden rock. As he performs the pose, he spreads sperm on them.

The eggs

The eggs are placed in strings, attached to the highest end of the shelter. These are characterized by having a large bud and because in their division they develop a germinal disk at the pole.

Embryonic development lasts from two to ten months, depending on the species. This period of time may vary, due to the temperature of the water. Thus, in cold waters, such as those of Alaska, the eggs could take up to ten months to reach their development.

During this stage, the female fervently takes care of the eggs, cleaning and aerating the area, as well as defending them from predators. While protecting them, the mother does not feed, so she dies shortly after hatching. As for the male, she dies a few weeks after having mated.

The babies

The vast majority of octopuses hatch as paralarvae. These are planktonic for several weeks or months, depending on the water temperature and the characteristics of the species. Its diet is based on larvae of arthropods or copepods, among others.

Later they settle on the seabed, becoming adults, without going through a process of metamorphosis. Benthic juveniles have a great ability to catch live prey. Also, they have a wide range of postural and chromatic responses, which allow them to hide from predators.

Diet and digestive system

Almost all members of the order Octopoda are predators. The octopuses that inhabit the seabed mainly feed on polychaete worms, crustaceans and other mollusks, such as clams. Those whose habitat is the open sea, eat fish, prawns and other cephalopods.

Each species, considering the habitat where it lives, has a particular diet. For example, the giant Pacific octopus hunts bivalve mollusks, such as scallops, clams, and cockles (Clinocardium nuttallii). It also catches some species of crustaceans, including the spider crab.

In particular, Enteroctopus dofleini tends to avoid moon snails, due to their large size. Likewise, it does not usually eat scallops, abalones and chitons, because they are strongly attached to the rocks.

Capture methods

The capture methods are usually very varied. One of these is that the octopus makes an attack and captures the prey, using the propulsion of water that comes out of the siphon. By taking it in his arms, he brings it to his mouth.

In the case of crustaceans, such as crabs, they inject their saliva, which has paralyzing effects. They then dismember them, using their beaks. In relation to the mollusks, he ingests them without the shell. To achieve this, you can separate them or pierce it. In this case, it passes through the shell and supplies toxic saliva through the hole.

In this way, the muscles of the prey relax and the soft tissues become easy to separate and consume. There are other ways of feeding, as in the case of the Grimpoteuthis, which swallows its food whole.

A very particular case is the genus Stauroteuthis, which inhabits deep waters. Species in this clade have special cells, known as photophores. These emit light, which is seen as points of light. In this way, manage to deceive the prey, directing it to the mouth.

Digestive system

The digestive system of the octopus is made up of a set of organs that are responsible for processing the ingested food. In this way, the necessary nutritional substances are obtained for the body to carry out all its vital functions.

The mouth has a chitinous beak, which helps to cut prey and detach the shells from bivalves, among other things. Inside the oral cavity is the radula, which is a muscular organ shaped like a tongue. In this are numerous rows of small keratinous teeth.

The salivary glands secrete a mucus, which lubricates the radula and groups the food particles, to be ingested. The food mass, which is found in the mouth, is carried to the esophagus, by the action of the lateral walls of this organ, in joint action with the radula.

The crop is located in the esophagus, where the pre-digested food is stored. Then, the food passes to the gastrointestinal tract, where the stomach, digestive glands, cecum and intestines are responsible for breaking down organic compounds and absorbing their nutrients. The waste is expelled to the outside through the anus.

Nervous system

The octopus is characterized by having the highest brain-body mass ratio of the entire group of invertebrates. Its nervous system is very complex, consisting of a central brain and two lobes.

The central brain is lined with a cartilaginous capsule and has approximately 40 million neurons. This nervous structure is made up of multiple lobes, which could be the product of the fusion of the ganglion system present in other mollusks.

In relation to the lobes, they are located outside the brain capsule. One of these is the optic lobe, made up of 160 million neurons. The other is the tentacle system, with about 330 million neurons.

In this way, the highest percentage of nerve cells in the octopus are in the nerve cords, located in its arms. Thus, these appendages have a variety of complex reflex actions, which persist even when they stop receiving nerve impulses.

Behavior

Defending

Octopuses can be threatened by seabirds, fish, cetaceans, pinnipeds, cephalopods, and man. To defend themselves, they usually hide or can camouflage themselves with the environment.

A clear example of mimicry occurs in the mimic octopus (Thaumoctopus mimicus). It has the ability to mimic the movements and physical appearance of more than 15 different species. Some of these are the sea serpent, starfish, lionfish, and jellyfish.

The imitations are carried out almost instantly, due to its great ability to vary skin colors and due to the high flexibility of the body. In addition, it can turn gray and pretend to be dead, remaining immobile for a long time.

Deimaticism

On the other hand, members of the Octopoda order tend to have deimatic behaviors. In these, the animal practices alarm or threat behaviors, to cause the predator to move away.

This occurs in the case of the bigeye octopus (Octopus macropus) and the common octopus (Octopus vulgaris). It exhibits eye rings, a pale hue, and dilated pupils. It also curls the arms, shoots jets of water and extends the membrane between the tentacles to the maximum.

In the case of the bigeye octopus, its skin turns a bright red-brown color, with numerous white spots.

ink

The octopus has a sac-like fold of skin, which is located below the digestive gland. A gland is attached to this, which is responsible for producing the ink, while the bag stores it. Before the ink leaves the body, it passes through different glands, where it mixes with mucus.

In this way, when it is expelled together with the water jet, the black spot stains the water, allowing the animal to escape from the predator. It can also shoot small drops of ink, which it uses as decoys to mislead the animal.

Ink doesn't just darken the water. Due to the action of the enzyme tyrosinase, it can also alter its taste and smell, confusing the predator.

Detachment of an arm

When under attack, some species can separate one of its appendages, from the base of it. As it falls, it keeps moving, it could even crawl on the seabed. In this way, the threat is distracted and the octopus escapes.

References

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