Octopus Volgaris
– Common Octopus –
| Conservation status |
|---|
 Least Concern (IUCN 3.1)[1] |
| Scientific classification |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Order: | Octopoda |
| Family: | Octopodidae |
| Genus: | Octopus |
| Species: | O. vulgaris |
The common octopus (Octopus vulgaris) is a mollusc belonging to the class Cephalopoda. Octopus vulgaris is the most studied of all octopus species. It is considered cosmopolitan, that is, a global species, which ranges from the eastern Atlantic, extends from the Mediterranean Sea and the southern coast of England, to at least Senegal in Africa. It also occurs off the Azores, Canary Islands, and Cape Verde Islands. The species is also common in the Western Atlantic. The common octopus hunts at dusk. Crabs, crayfish, and bivalve molluscs (two-shelled, such as cockles) are preferred, although the octopus eats almost anything it can catch. It is able to change colour to blend in with its surroundings, and is able to jump upon any unwary prey that strays across its path. Using its beak, it is able to break into the shells of shelled molluscs. Training experiments have shown the common octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects.
The octopus uses gills as its respiratory surface. The gill is composed of branchial ganglia and a series of folded lamellae. Primary lamellae extend out to form demibranches and are further folded to form the secondary free-folded lamellae, which are only attached at their tops and bottoms.[2] The tertiary lamellae are formed by folding the secondary lamellae in a fan-like shape.[2] Water moves slowly in one direction over the gills and lamellae, into the mantle cavity and out of the octopus’ funnel.[3] The octopus has three hearts, one main two-chambered heart charged with sending oxygenated blood to the body and two smaller branchial hearts, one next to each set of gills. The circulatory circuit sends oxygenated blood from the gills to the atrium of the systemic heart, then to its ventricle which pumps this blood to the rest of the body. Deoxygenated blood from the body goes to the branchial hearts, which pump the blood across the gills to oxygenate it, and then the blood flows back to the systemic atrium for the process to begin again.
Characteristics
DESCRIPTION
The body of the octopus consists of a globular head with eyes on each side characterized by their horizontal pupil . The head is extended by a muscular body (the mantle) which contains the organs. The mantle * is divided into several tentacular lobes furnished with two rows of suction cups. The eight star-shaped arms are united by an inter-brachial membrane and form a crown in the center of which the buccal bulb opens with the ” parrot’s beak “. The ventral part of the mantle is cut by a wide slit (palleal slit) towards the palleal cavity * where the gills * (respiration) and viscera are located. From this cavity an inverted funnel, thelateral siphon, forms a sort of nozzle which is used to expel water from the palleal cavity under the effect of the contractions of the mantle. The principle of reaction produced by this funnel allows a propulsive movement unique in nature.
The adult octopus has an average weight of around 3 kilograms, and although rare, 10 kilogram individuals have been reported. The size of about 60 cm can sometimes reach 1.20 m in females and 1.30 m in males.
Biotope
The characteristic habitat of the octopus is the benthic coastal bedrock environment, from the shores to the upper limit of the continental shelf (about 150 m). Numerous observations show that the density of octopus decreases with depth.
The coralligenous * and the rocky masses are favored by the octopuses, but the sandy or muddy bottoms and the seagrass beds are in some areas very frequented. The mimetic faculties of the octopus allow it to merge with any environment.
Homebody, the octopus has a territorial behavior, each animal has its own lodging. Sedentary, however, it seems to obey migration during the spawning period (temperate zones where reproduction is seasonal).
Similar Species
Callistoctopus macropus (or nocturnal octopus) which is recognizable by its thinner tentacles and marked with a row of phosphorescent white dots.
Genus Eledone :
Eledons have only one row of suckers on their arms and are less mimetic. They live at greater depth.
Alimentation
A carnivorous animal, the octopus feeds mainly on crustaceans, cephalopod and bivalve molluscs and very rarely on fish.
To feed, the octopus successively implements:
– the action of the arms and suction cups to capture prey and transport to the roost.
– the mechanical action of the “parrot’s beak” mandibles to shred crustaceans or of the radula * to pierce the shell of bivalves.
– the chemical action of a venom, the cephalotoxin * which paralyzes the prey beforehand. This venom is capable of killing a rabbit.
The hard parts of the carapaces and shells are rejected. The octopus roost is very often marked by an agglomeration of waste to hide the entrance.
The octopus does not disdain to enter into unfair competition with fishermen by taking crustaceans in fishing devices (traps, pots).
Reproduction
Sexual maturity:
– males are mature as soon as their weight reaches 200 g.
– females, even the smallest, are at 500 g.
Display: The female solicits the partner by obstinately cleaning her suction cups; the male responds by showing his own and extending his arms to the female. At the same time, the eyes are surrounded by a dark circle.
Mating: the male uses his third arm (on the right starting from the middle of the head), the hectocotyle *, modified into a spatula at the end and traversed along its length by a gutter. It introduces the hectocotyl into the female’s palleal cavity to inject the oviduct * spermatophores * into the oviduct.
The spermatophores will release, in a gland of the oviduct, a quantity of spermatozoa * which will fertilize the ova as they pass through the oviduct. This gland also provides the rods and mucus for the attachment of the eggs.
Spawning period: March to November, three to eight weeks after mating depending on the water temperature.
The female lays her eggs (100,000 to 500,000 – length about 2 mm – agglomerated in about fifty cords) by fixing them to the ceiling of her laying cave. The height of the cords depends on the ceiling height. The laying can last from two to four weeks.
Incubation: The female will ventilate her laying until hatching (from 24 to 125 days depending on the temperature), without feeding during this entire period. She dies at the end of the
Various Biology
Outside the breeding season, the octopus is solitary. The social distance between two individuals is around thirty meters. This behavior has been taken advantage of by fishermen, who since antiquity have offered octopus individual lodgings, gargoulettes (amphorae and roped pottery) to fish it.
The octopus has highly developed camouflage abilities, which combine posture, skin structure and colors. The coloring is done by the chromatophores *: pigmented cells of the dermis, very specialized which, varying in size (two to sixty times), spread the contents of a pigment bag and thus produce different shades from the starting pigment (yellow, orange , red, often brown, and black).
Associated with other cells of fixed size, the iridophores (high refraction) and the leucophores (dispersion of light), and superimposed in 4 or 5 layers, the chromatophores allow all the skin patterns used by the octopus for its mimicry. .
In case of danger, the octopus has an asset which allows it to hide its flight and deceive the predator. An “ink cloud” drawn from the “black pocket” is emitted in small jets. This dark lure which seems to draw the shape of an octopus can persist for about ten minutes. Present in many cephalopods, this pocket opens into the intestine, near the anus. It has a glandular part which produces melanin, and a reservoir part where the pigment mixed with the mucus forms the “ink”.
Les bras ou tentacules très souples, préhensiles peuvent porter jusqu’à 240 ventouses. Ces dernières constituées de parois musculaires cylindriques et d’un disque souple radié, assurent une adhérence parfaite sur tous les supports. Elles sont très sensitives et participent à l’homochromie. Le poulpe se sert de ces ventouses pour intimider les intrus et également pour parader à l’époque du frai. Le poulpe subit de fréquentes amputations totales ou partielles sur les tentacules de la part de ses prédateurs, congres, murènes, crustacés. Mais il est capable de régénérer ou reconstituer le tentacule amputé.
The eyes are of a perfection close to that of vertebrates (goat). They have the same composition: cornea, iris, lens, retina and two eyelids. The look of the octopus is characterized by the black rectangular pupil in the center of the eye. If the sight is solicited by something, the octopus is very curious, the eyes go up. They are mobile and look in all directions.
Master of its territory, the octopus moves there, hunts there, surveying the seabed. He leans on his arms or even crawls while moving forward or backward in a nonchalant manner without haste. If the need arises, the octopus can move very quickly. He uses propulsion. This reaction results from the contractions of the mantle which expel the water contained in the palleal cavity, through a funnel, the siphon *. The propulsion is opposed to the current of the water rejected by the very mobile siphon which serves as rudder. The running speed is regulated by the spacing of the arms against the body.
During the fall of 2007, scientists (Guerra et al., 2007), following the processing of images of a common octopus harassed by fish off the Balearic Islands, reportedly detected on the soundtrack recorded by the camera, a sharp sound, like a gunshot, clearly emitted by the octopus defending itself, accompanied on the images by a flash of light. According to researchers at the Vigo Marine Research Institute, it would be a phenomenon of cavitation “this noise could have been produced by an extraordinarily powerful contraction of the octopus’ mantle in a situation of extreme danger”. The incidence of sunlight through the bubbles generated by the emission of the “gunshot” could explain the observed flash of light.
This sound strategy would therefore be an ultimate defense mechanism to escape predators. But it would require such an expenditure of energy that the octopus would only use it very rarely. Which would explain the late discovery of this strange new asset of the octopus.
The octopus is capable of autotomy * (an arm can be detached at a determined place, or be cut by its owner to escape a predator), but also of autophagy, which is very different. This autophagy process can have two causes. The first is not clearly elucidated, it would be the effect of a pathogenic substance produced by the animal itself, or more probably of an infectious disease attacking the nervous system. Incubation would take between one and two weeks and death would occur one to two days after the onset of autophagy behavior. This disease can appear at any age. The second cause is better known, it is an effect of senescence which strikes the male octopus after its sexual maturity and its period of reproductive activity. It is characterized by a gradual loss of appetite, disorderly hyperactivity, white lesions on the body, the most dramatic effect being loss of control of body movements. This loss particularly affects the arms, which go in all directions interfering with each other, and can lead to autophagy, the octopus consuming its tentacles. The few females that survive the hatching of their eggs similarly go into senescence. the octopus consuming its tentacles. The few females that survive hatching from their eggs similarly go into senescence. the octopus consuming its tentacles. The few females that survive hatching from their eggs similarly go into senescence.
Further Information
Rare and poorly explained observation: the “Civa dance”.
Only one observation of this spectacle, also seen by other divers: the octopus (female?) Came out of its hole and began to “dance” in front of the group, the tentacles twisting in all directions like the Apsara of Asia, some entering and leaving the palleal cavity like undulating snakes, surrounding themselves by vibrating around the body or even undulating in open water. Another octopus from behind came up close to the first one. Subjected to the curiosity of divers, he began to crawl further. Resumption of the observation of the first octopus, he resumed his display. The scientists consulted are thinking of a deworming session. It could also be the sad spectacle given by a senescent octopus.
Many divers “traumatize” octopuses by “playing” with them until they spray their ink. The defenses of underwater organisms are not games. The metabolism implemented for these protections requires a strong energy expenditure by the animal which is far from considering it as a game. The octopus is playful but let it take the initiative.
Octopuses, like most cephalopods, are highly prized in gastronomy. They have been fished all over the Mediterranean basin since antiquity. Although part of the economic resource of fisheries, the octopus is not an endangered species.
Octopus vulgaris grows to 25 cm in mantle length with arms up to 1 m long.[4] O. vulgaris is caught by bottom trawls on a huge scale off the northwestern coast of Africa. More than 20,000 tonnes are harvested annually.[4]
The common octopus hunts at dusk. Crabs, crayfish, and bivalve molluscs (such as cockles) are preferred, although the octopus eats almost anything it can catch. It is able to change colour to blend in with its surroundings, and is able to jump upon any unwary prey that strays across its path. Using its beak, it is able to break into the shells of shelled molluscs. It also possesses venom to subdue its prey.[citation needed]
Training experiments have shown the common octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects. They are intelligent enough to learn how to unscrew a jar and are known to raid lobster traps.[5][6] O. vulgaris was the first invertebrate animal protected by the Animals (Scientific Procedures) Act 1986 in the UK;[7] it was included because of its high intelligence.[citation needed]
Physiology
Habitat and Demands
The common octopus is typically found in tropical waters throughout the world, such as the Mediterranean Sea and East Atlantic.[8] They prefer the floor of relatively shallow, rocky, coastal waters, often no deeper than 200 m.[8] Although they prefer around 36 grams per liter, salinity throughout their global habitat is found to be between roughly 30 and 45 grams of salt per liter of water.[9] They are exposed to a wide variety of temperatures in their environments, but their preferred temperature ranges from about 15 to 16 °C.[9] In especially warm seasons, the octopus can often be found deeper than usual to escape the warmer layers of water.[10] In moving vertically throughout the water, the octopus is subjected to various pressures and temperatures, which affect the concentration of oxygen available in the water.[9] This can be understood through Henry’s law, which states that the concentration of a gas in a substance is proportional to pressure and solubility, which is influenced by temperature. These various discrepancies in oxygen availability introduce a requirement for regulation methods.[11]
Primarily, the octopus situates itself in a shelter where a minimal amount of its body is presented to the external water, which would pose a problem for an organism that breathes solely through its skin.[12] When it does move, most of the time it is along the ocean or sea floor, in which case the underside of the octopus is still obscured.[12] This crawling increases metabolic demands greatly, requiring they increase their oxygen intake by roughly 2.4 times the amount required for a resting octopus.[13] This increased demand is met by an increase in the stroke volume of the octopus’ heart.[14]
The octopus does sometimes swim throughout the water, exposing itself completely.[9] In doing so, it uses a jet mechanism that involves creating a much higher pressure in its mantle cavity that allows it to propel itself through the water.[14] As the common octopus’ heart and gills are located within its mantle, this high pressure also constricts and puts constraints on the various vessels that are returning blood to the heart.[14] Ultimately, this creates circulation issues and is not a sustainable form of transportation, as the octopus cannot attain an oxygen intake that can balance the metabolic demands of maximum exertion.[14]
Respiration
The octopus uses gills as its respiratory surface. The gill is composed of branchial ganglia and a series of folded lamellae. Primary lamellae extend out to form demibranches and are further folded to form the secondary free folded lamellae, which are only attached at their tops and bottoms.[2] The tertiary lamellae are formed by folding the secondary lamellae in a fan-like shape.[2] Water moves slowly in one direction over the gills and lamellae, into the mantle cavity and out of the octopus’ funnel.[3]
The structure of the octopus’ gills allows for a high amount of oxygen uptake; up to 65% in water at 20⁰C.[3] The thin skin of the octopus accounts for a large portion of in-vitro oxygen uptake; estimates suggest around 41% of all oxygen absorption is through the skin when at rest.[12] This number is affected by the activity of the animal – the oxygen uptake increases when the octopus is exercising due to its entire body being constantly exposed to water, but the total amount of oxygen absorption through skin is actually decreased to 33% as a result of the metabolic cost of swimming.[12] When the animal is curled up after eating, its absorption through its skin can drop to 3% of its total oxygen uptake.[12] The octopus’ respiratory pigment, hemocyanin, also assists in increasing oxygen uptake.[11] Octopuses can maintain a constant oxygen uptake even when oxygen concentrations in the water decrease to around 3.5 kPa[3] or 31.6% saturation (standard deviation 8.3%).[11] If oxygen saturation in sea water drops to about 1–10% it can be fatal for Octopus vulgaris depending on the weight of the animal and the water temperature.[11] Ventilation may increase to pump more water carrying oxygen across the gills but due to receptors found on the gills the energy use and oxygen uptake remains at a stable rate.[3] The high percent of oxygen extraction allows for energy saving and benefits for living in an area of low oxygen concentration.[2]
Water is pumped into the mantle cavity of the octopus, where it comes into contact with the internal gills. The water has a high concentration of oxygen compared to the blood returning from the veins, so oxygen diffuses into the blood. The tissues and muscles of the octopus use oxygen and release carbon dioxide when breaking down glucose in the Krebs cycle. The carbon dioxide then dissolves into the blood or combines with water to form carbonic acid, which decreases blood pH. The Bohr effect explains why oxygen concentrations are lower in venous blood than arterial blood and why oxygen diffuses into the bloodstream. The rate of diffusion is affected by the distance the oxygen has to travel from the water to the bloodstream as indicated by Fick’s laws of diffusion. Fick’s laws explain why the gills of the octopus contain many small folds that are highly vascularised. They increase surface area, thus also increase the rate of diffusion. The capillaries that line the folds of the gill epithelium have a very thin tissue barrier (10 µm), which allows for fast, easy diffusion of the oxygen into the blood.[15] In situations where the partial pressure of oxygen in the water is low, diffusion of oxygen into the blood is reduced,[16] Henry’s law can explain this phenomenon. The law states that at equilibrium, the partial pressure of oxygen in water will be equal to that in air; but the concentrations will differ due to the differing solubility. This law explains why O. vulgaris has to alter the amount of water cycled through its mantle cavity as the oxygen concentration in water changes.[3]
The gills are in direct contact with water – carrying more oxygen than the blood – that has been brought into the mantle cavity of the octopus. Gill capillaries are quite small and abundant, which creates an increased surface area that water can come into contact with, thus resulting in enhanced diffusion of oxygen into the blood. Some evidence indicates that lamellae and vessels within the lamellae on the gills contract to aid in propelling blood through the capillaries.[17]
Circulation
The octopus has three hearts, one main two-chambered heart charged with sending oxygenated blood to the body and two smaller branchial hearts, one next to each set of gills. The circulatory circuit sends oxygenated blood from the gills to the atrium of the systemic heart, then to its ventricle which pumps this blood to the rest of the body. Deoxygenated blood from the body goes to the branchial hearts which pump the blood across the gills to oxygenate it, and then the blood flows back to the systemic atrium for the process to begin again.[18] Three aortae leave the systemic heart, two minor ones (the abdominal aorta and the gonadal aorta) and one major one, the dorsal aorta which services most of the body.[19] The octopus also has large blood sinuses around its gut and behind its eyes that function as reserves in times of physiologic stress.[20]
The octopus’ heart rate does not change significantly with exercise, though temporary cardiac arrest of the systemic heart can be induced by oxygen debt, almost any sudden stimulus, or mantle pressure during jet propulsion.[21] Its only compensation for exertion is through an increase in stroke volume of up to three times by the systemic heart,[21] which means it suffers an oxygen debt with almost any rapid movement.[21][22] The octopus is, however, able to control how much oxygen it pulls out of the water with each breath using receptors on its gills,[3] allowing it to keep its oxygen uptake constant over a range of oxygen pressures in the surrounding water.[21] The three hearts are also temperature and oxygen dependent and the beat rhythm of the three hearts are generally in phase with the two branchial hearts beating together followed by the systemic heart.[18] The Frank–Starling law also contributes to overall heart function, through contractility and stroke volume, since the total volume of blood vessels must be maintained, and must be kept relatively constant within the system for the heart to function properly.[23]
The blood of the octopus is composed of copper-rich hemocyanin, which is less efficient than the iron-rich hemoglobin of vertebrates, thus does not increase oxygen affinity to the same degree.[24] Oxygenated hemocyanin in the arteries binds to CO2, which is then released when the blood in the veins is deoxygenated. The release of CO2 into the blood causes it to acidify by forming carbonic acid.[25] The Bohr effect explains that carbon dioxide concentrations affect the blood pH and the release or intake of oxygen. The Krebs cycle uses the oxygen from the blood to break down glucose in active tissues or muscles and releases carbon dioxide as a waste product, which leads to more oxygen being released. Oxygen released into the tissues or muscles creates deoxygenated blood, which returns to the gills in veins. The two brachial hearts of the octopus pump blood from the veins through the gill capillaries. The newly oxygenated blood drains from the gill capillaries into the systemic heart, where it is then pumped back throughout the body.[18]
Blood volume in the octopus’ body is about 3.5% of its body weight[20] but the blood’s oxygen-carrying capacity is only about 4 volume percent.[21] This contributes to their susceptibility to the oxygen debt mentioned before. Shadwick and Nilsson[22] concluded that the octopus circulatory system is “fundamentally unsuitable for high physiologic performance”. Since the binding agent is found within the plasma and not the blood cells, a limit exists to the oxygen uptake that the octopus can experience. If it were to increase the hemocyanin within its blood stream, the fluid would become too viscous for the myogenic[26] hearts to pump.[23] Poiseuille’s law explains the rate of flow of the bulk fluid throughout the entire circulatory system through the differences of blood pressure and vascular resistance.[23]
Like those of vertebrates, octopus blood vessels are very elastic, with a resilience of 70% at physiologic pressures. They are primarily made of an elastic fibre called octopus arterial elastomer, with stiffer collagen fibres recruited at high pressure to help the vessel maintain its shape without over-stretching.[27] Shadwick and Nilsson[28] theorized that all octopus blood vessels may use smooth-muscle contractions to help move blood through the body, which would make sense in the context of them living under water with the attendant pressure.
The elasticity and contractile nature of the octopus aorta serves to smooth out the pulsing nature of blood flow from the heart as the pulses travel the length of the vessel, while the vena cava serves in an energy-storage capacity.[28] Stroke volume of the systemic heart changes inversely with the difference between the input blood pressure through the vena cava and the output back pressure through the aorta.
Osmoregulation
The hemolymph, pericardial fluid and urine of cephalopods, including the common octopus, are all isosmotic with each other, as well as with the surrounding sea water.[29] It has been suggested that cephalopods do not osmoregulate, which would indicate that they are conformers.[29] This means that they adapt to match the osmotic pressure of their environment, and because there is no osmotic gradient, there is no net movement of water from the organism to the seawater, or from the seawater into the organism.[29] Octopuses have an average minimum salinity requirement of 27g/l, and that any disturbance introducing significant amounts of fresh water into their environment can prove fatal.[30]
In terms of ions, however, a discrepancy does seem to occur between ionic concentrations found in the seawater and those found within cephalopods.[29] In general, they seem to maintain hypoionic concentrations of sodium, calcium, and chloride in contrast to the salt water.[29] Sulfate and potassium exist in a hypoionic state, as well, with the exception of the excretory systems of cephalopods, where the urine is hyperionic.[29] These ions are free to diffuse, and because they exist in hypoionic concentrations within the organism, they would be moving into the organism from the seawater.[29] The fact that the organism can maintain hypoionic concentrations suggests not only that a form of ionic regulation exists within cephalopods, but also that they also actively excrete certain ions such as potassium and sulfate to maintain homeostasis.[29]
O. vulgaris has a mollusc-style kidney system, which is very different from mammals. The system is built around an appendage of each branchial heart, which is essentially an extension of its pericardium.[29] These long, ciliated ducts filter the blood into a pair of kidney sacs, while actively reabsorbing glucose and amino acids into the bloodstream.[29] The renal sacs actively adjust the ionic concentrations of the urine, and actively add nitrogenous compounds and other metabolic waste products to the urine.[29] Once filtration and reabsorption are complete, the urine is emptied into O. vulgaris’ mantle cavity via a pair of renal papillae, one from each renal sac.[29]
Temperature and body size directly affect the oxygen consumption of O. vulgaris, which alters the rate of metabolism.[13] When oxygen consumption decreases, the amount of ammonia excretion also decreases due to the slowed metabolic rate.[13] O. vulgaris has four different fluids found within its body: blood, pericardial fluid, urine, and renal fluid. The urine and renal fluid have high concentrations of potassium and sulphate, but low concentrations of chloride. The urine has low calcium concentrations, which suggests it has been actively removed. The renal fluid has similar calcium concentrations to the blood. Chloride concentrations are high in the blood, while sodium varies. The pericardial fluid has concentrations of sodium, potassium, chlorine and calcium similar to that of the salt water supporting the idea that O. vulgaris does not osmoregulate, but conforms. However, it has lower sulphate concentrations.[29] The pericardial duct contains an ultrafiltrate of the blood known as the pericardial fluid, and the rate of filtration is partly controlled by the muscle- and nerve-rich branchial hearts.[29] The renal appendages move nitrogenous and other waste products from the blood to the renal sacs, but do not add volume. The renal fluid has a higher concentration of ammonia than the urine or the blood, thus the renal sacs are kept acidic to help draw the ammonia from the renal appendages. The ammonia diffuses down its concentration gradient into the urine or into the blood, where it gets pumped through the branchial hearts and diffuses out the gills.[29] The excretion of ammonia by O. vulgaris makes them ammonotelic organisms. Aside from ammonia, a few other nitrogenous waste products have been found to be excreted by O. vulgaris such as urea, uric acid, purines, and some free amino acids, but in smaller amounts.[29]
Within the renal sacs, two recognized and specific cells are responsible for the regulation of ions. The two kinds of cells are the lacuna-forming cells and the epithelial cells that are typical to kidney tubules. The epithelia cells are ciliated, cylindrical, and polarized with three distinct regions. These three regions are apical, middle cytoplasmic, and basal lamina. The middle cytoplasmic region is the most active of the three due to the concentration of multiple organelles within, such as mitochondria and smooth and rough endoplasmic reticulum, among others. The increase of activity is due to the interlocking labyrinth of the basal lamina creating a crosscurrent activity similar to the mitochondrial-rich cells found in teleost marine fish. The lacuna-forming cells are characterized by contact to the basal lamina, but not reaching the apical rim of the associated epithelial cells and are located in the branchial heart epithelium. The shape varies widely and are occasionally more electron-dense than the epithelial cells, seen as a “diffused kidney” regulating ion concentrations.[31]
One adaptation that O. vulgaris has is some direct control over its kidneys.[29] It is able to switch at will between the right or left kidney doing the bulk of the filtration, and can also regulate the filtration rate so that the rate does not increase when the animal’s blood pressure goes up due to stress or exercise.[29] Some species of octopuses, including O. vulgaris, also have a duct that runs from the gonadal space into the branchial pericardium.[29] Wells[29] theorized that this duct, which is highly vascularized and innervated, may enable the reabsorption of important metabolites from the ovisac fluid of pregnant females by directing this fluid into the renal appendages.
Thermoregulation
As an oceanic organism, O. vulgaris experiences a temperature variance due to many factors, such as season, geographical location, and depth.[32] For example, octopuses living around Naples may experience a temperature of 25°C in the summer and 15°C in the winter.[32] These changes would occur quite gradually, however, and thus would not require any extreme regulation.
The common octopus is a poikilothermic, eurythermic ectotherm, meaning that it conforms to the ambient temperature.[33] This implies that no real temperature gradient is seen between the organism and its environment, and the two are quickly equalized. If the octopus swims to a warmer locale, it gains heat from the surrounding water, and if it swims to colder surroundings, it loses heat in a similar fashion.
O. vulgaris can apply behavioral changes to manage wide varieties of environmental temperatures. Respiration rate in octopods is temperature-sensitive – respiration increases with temperature.[34] Its oxygen consumption increases when in water temperatures between 16 and 28°C, reaches a maximum at 28°C, and then begins to drop at 32°C.[34] The optimum temperature for metabolism and oxygen consumption is between 18and 24°C.[34] Variations in temperature can also induce a change in hemolymph protein levels along oxygen consumption.[34] As temperature increases, protein concentrations increase in order to accommodate the temperature. Also the cooperativity of hemocyanin increases, but the affinity decreases.[35] Conversely, a decrease in temperature results in a decrease in respiratory pigment cooperativity and increase in affinity.[35] The slight rise in P50 that occurs with temperature change allows oxygen pressure to remain high in the capillaries, allowing for elevated diffusion of oxygen into the mitochondria during periods of high oxygen consumption.[35] The increase in temperature results in higher enzyme activity, yet the decrease in hemocyanin affinity allows enzyme activity to remain constant and maintain homeostasis. The highest hemolymph protein concentrations are seen at 32°C and then drop at temperatures above this.[34] Oxygen affinity in the blood decreases by 0.20 kPa/°C at a pH of 7.4.[35] The octopod’s thermal tolerance is limited by its ability to consume oxygen, and when it fails to provide enough oxygen to circulate at extreme temperatures the effects can be fatal.[34] O. vulgaris has a pH-independent venous reserve that represents the amount of oxygen that remains bound to the respiratory pigment at constant pressure of oxygen. This reserve allows the octopus to tolerate a wide range of pH related to temperature.[35]
As a temperature conformer,[36] O. vulgaris does not have any specific organ or structure dedicated to heat production or heat exchange. Like all animals, they produce heat as a result of ordinary metabolic processes such as digestion of food,[32] but take no special means to keep their body temperature within a certain range. Their preferred temperature directly reflects the temperature to which they are acclimated.[36] They have an acceptable ambient temperature range of 13–28°C,[36] with their optimum for maximum metabolic efficiency being about 20°C.[33]
As ectothermal animals, common octopuses are highly influenced by changes in temperature. All species have a thermal preference where they can function at their basal metabolic rate.[36] The low metabolic rate allows for rapid growth, thus these cephalopods mate as the water becomes closest to the preferential zone. Increasing temperatures cause an increase in oxygen consumption by O. vulgaris.[13] Increased oxygen consumption can be directly related to the metabolic rate, because the breakdown of molecules such as glucose requires an input of oxygen, as explained by the Krebs cycle. The amount of ammonia excreted conversely decreases with increasing temperature.[13] The decrease in ammonia being excreted is also related to the metabolism of the octopus due to its need to spend more energy as the temperature increases. Octopus vulgaris will reduce the amount of ammonia excreted in order to use the excess solutes that it would have otherwise excreted due to the increased metabolic rate. Octopuses do not regulate their internal temperatures until it reaches a threshold where they must begin to regulate to prevent death.[13] The increase in metabolic rate shown with increasing temperatures is likely due to the octopus swimming to shallower or deeper depths to stay within its preferential temperature zone.
