"ghostly" octopuses are under the threat of extinction because of the touching care for offspring. How cephalopods take care of their offspring Care and care

Sharks have always posed unsolvable questions and riddles to scientists. The secrets that envelop these mighty ocean creatures have long turned into legends.

Scientists have always wondered: why don't sharks take care of their offspring? Only a few species can boast of these abilities. It would be logical to assume that a huge toothy mother, having given birth to a tiny shark, will immediately swim to get food for him, teach the baby, protecting and protecting.

Instead, the bloodthirsty new mother, having given birth to an heir, heartlessly sails away, not even thinking about the joys of maternal instinct. Why? Do sharks really not care about the preservation of the genus, species, if you think globally?

Sharks don't care about their offspring

It turns out that even in matters of motherhood, these fish bypassed other creatures. Yes, sharks do not have a maternal instinct in the conventional sense. These predators take care of the baby in a different way, and hardly anyone will dispute the thoughtfulness and expediency of their methods.

It is known that in the majority of ovoviviparous and viviparous species, the so-called "intrauterine starvation" is common. This means that the largest and strongest of the young inside the mother's womb can eat their less fortunate counterparts.

At the same time, the shark's body often arranges "intrauterine starvation" for babies - it completely or partially reduces the supply of oxygen and nutrients from the maternal circulation to the yolk sac.

Watch the video - Intrauterine shark cannibalism:

That is, the body of an adult shark itself stimulates the young to hunt, show aggression, and survive. And toothy babies are born quite adapted to the conditions cruel world- they know how to protect themselves, find prey, hide from a hungry pursuer.

Newborn babies have a well-developed musculoskeletal system, an arsenal of sharp teeth and an excellent sense of smell - a complete set of an ideal predator.

As you know, the liver for these fish is the key to buoyancy and the main source of nutrients.

So, it has been proven that the liver of a newborn baby shark makes up about 20% of the total mass of its body, while the liver of an adult predator takes only 6% of its powerful body.

A large liver allows the little ones to go without food for a long time until they perfect their initial hunting techniques.

As you grow older, the size of this organ decreases.

Shark breeding features

Interestingly, all sharks give birth to a relatively small number of sharks - from 1-2 to 9-11 individuals. Even oviparous species lay about a dozen eggs. There is an exception - it lays almost 500 eggs, however, this cannot be compared with a million eggs of other predators.

In this way, weak and small heirs are culled, and the offspring of sharks are born obviously healthy.

The mechanisms of preparing the mother's body for the birth of a baby are also interesting. It turns out that immediately before childbirth, the level of cortisol, the stress hormone, decreases sharply in the blood of a female shark, and the amount increases. But why?

It turns out that these adaptation processes are also a kind of care for offspring: immediately after birth, a born predator will swim away, and will not rush at her cub. But if in a few hours the mother stumbles upon a shark, then with a high degree of probability she will open a hunt for him.

Babies in shallow water - and this is also one of the ways to protect offspring. Near the shore, a toothy baby is less likely to meet adults or other hungry aggressors.

Watch video - Shark gives birth:

If sharks, like many other species, nursed their young, protected them from danger, they would not have conquered all the expanses of water. And with the perfect ways of caring and educating these bloodthirsty fish, sharks have every chance to outlive the existing inhabitants of the ocean.

Babies are born unique, ready to attack killers - no species, even land mammals, can boast of such abilities of their young.

Thus, sharks are almost the only creatures of the World Ocean, whose maternal instincts are not aimed at preserving the number of offspring, but at preserving the quality of genetic material, giving birth and raising the strongest and most enduring cub - the future owner of salty ocean waters.

Cephalopods are the most highly organized of all representatives of their type. class of cephalopods ( Cephalopoda) is divided into two subclasses: four-branched ( Tetrabranchia) with a single order, family and genus of nautilus ( Nautilus) and bibranchs ( Dibranchia) with four units: octopuses ( Octopoda), vampires ( Vampyromorpha), cuttlefish ( Sepiida) and squid ( Teuthida).

Even the most primitive of cephalopods, the nautilus, take care of their offspring. For example, females Nautilus pompilius, laying the largest eggs among cephalopods (up to 4 cm in length), carry out this process very responsibly. The female lays eggs on the bottom one by one with long (two weeks) breaks. Usually nautiluses live at a depth of up to 500 m, but for laying eggs they rise to the very shallow water, where the temperature reaches 27-28 ° C. At the same time, the female hides her eggs so carefully that so far no researcher has ever seen nautilus eggs in nature. Only recently, after many failures, these mollusks have been propagated in aquariums. It turned out that the period of incubation of their eggs is 11-14 months.

Eggs of some species of octopuses develop for no less time. Moreover, the females of many representatives of this order “hatch” their clutch without leaving it for a minute: they constantly sort out the eggs, clean them, and wash them with fresh water from the funnel. In some species, the female diligently weaves the stems of small eggs into a long bunch with her sensitive tentacles and attaches it to the ceiling of an underwater cave with a drop of special glue, in which there can be more than one hundred such bunches. In species that lay large eggs, the female attaches them to the ceiling one by one.

During the entire period of egg development, females of "incubating" species of octopuses do not feed, accumulating a supply of nutrients in their bodies in advance. Before breeding, they completely stop producing digestive enzymes.

Female sand octopus (Bathypolypus arcticus), living in the waters of Primorye and near Northern Japan, takes care of its clutch for about a year. And the arctic octopus bathypolypus ( Bathypolypus arcticus) that lives in our northern seas, "hatch" eggs for 12-14 months. After the babies are born, the emaciated female dies. A similar phenomenon - death after the completion of a single breeding cycle - is generally very characteristic of female cephalopods. But their males sometimes survive 2-3 breeding seasons.

Before her death, the female octopus must help the babies hatch from the eggs. In an aquarium, without a mother, the hatching process of octopuses is very long, and it takes up to two months from the birth of the first cub to the hatching of the last one in the same clutch. With a living mother, the cubs are born in one night. Perhaps the octopus gives them some specific signal, because small mollusks already see well before hatching and move quite actively in their transparent egg shell.

Cephalopod eggs: 1 - Eledone; 2 - Cirroctopus; 3 - Loligo; 4-Sepia

Other representatives of the two-gill cephalopods do not incubate eggs as carefully as octopuses, but take care of their safety in other ways. For example, cuttlefish, laying their eggs on the bottom, mask them either with ink, or covering the masonry with empty mollusk shells, or even tying the eggs to the stalks of stinging corals. One species of cuttlefish stuffs its eggs into soft silicon-horn sponges. The development of cuttlefish eggs in northern waters may likely to continue for more than six months.

As for squids, in known oceanic species, the clutch is a gelatinous formation with eggs suspended in it. The most important commercial species Todarodes pacificus and Illex illecebrosus these are huge, 1 m in diameter, balls of transparent mucus, which contain hundreds of thousands of small eggs. And the little firefly squid ( Watasenia scintillans) are two transparent threads of mucus in which clam eggs are enclosed. In warm and moderate warm waters small squid eggs develop in 5–10, sometimes up to 15 days.

The eyes of a bivalve mollusc.

Octopus.

When danger approaches, cephalopods throw a jet of black liquid into the water. The “ink” blurs in the water, and under this thick black cloud the mollusk escapes safely. Cephalopods are real underwater chameleons: they can quickly change skin color. If you make an octopus angry, he will instantly change grey colour to black, and when calmed down, it turns gray again.

Among the most simply arranged cephalopods - nautiluses, or pearl boats. Nautilus, unlike most cephalopods, have a multi-chambered shell. Growing up, the mollusk builds more and more spacious chambers for itself and each time settles in the last, largest. Filling the remaining chambers with water or air, it can float up or sink to the bottom. Jewelry and buttons are made from the shells of pearl boats.

Animals with 8 tentacles belong to the order of octopuses. One of the notable features of common octopuses is selfless care for offspring. The female octopus vigilantly guards the laid eggs. As I.I. Akimushkin about one octopus mother who laid her eggs in captivity, “if any of the servants dared to throw a piece of meat to her very head, Mephisto flashed brick red in anger, freed her hand from an impromptu basket and discarded her previously beloved food - after all, this "garbage" could have landed on her precious balls!"

Octopus eggs.

Octopus development.

Nautilus.

Cuttlefish, in the words of the British naturalist Frank Lane, "literally left a mark on human culture." After all for a long time people wrote it in ink. No less valued is the famous “bone” (remnant of the shell) of cuttlefish, which is harvested on the seashore. It is used as a drawing eraser, in crushed form - as an additive to tooth powder, as well as medicine.

An octopus species unknown to science. The unusual creature was nicknamed Casper for its milky color and resemblance to the Disney character.

Marine biologists have come to the conclusion that due to a number of differences from their relatives, we can talk about the discovery of not only a new species, but also a whole new genus of octopuses. The fact is that this octopus lives at an incredible depth for cephalopods - more than four thousand meters. Casper has no fins, and all suckers are arranged in one row on each limb, which is also uncharacteristic of octopuses. In addition, the representative of the new species completely lacks pigment cells - chromatophores. That is why the creature is almost transparent.

A team of scientists led by Autun Purser from the Institute of Polar and Marine Research. Alfred Wegener, observed 30 individuals using remote-controlled underwater vehicles.

The discovery made by scientists turned out to be surprising and frightening at the same time. They were able to find out that "ghostly" octopuses are characterized by an unusual parenting strategy. She would be a real gift for scientific community, if not one but: it is because of it that a unique species is threatened with extinction.

Female "ghostly" octopuses take care of the eggs until the offspring hatch. because of low temperatures, prevailing at great depths, this happens for quite a long time - sometimes up to several years (although after scientists it is already difficult to surprise with the timing).

At the same time, the strategy of caring for offspring, as the researchers note, turned out to be incredibly touching in these octopuses: the female wraps her whole body around the eggs and protects them from other deep-sea inhabitants, without even sailing off to get her own food. As a result, almost always she dies when the cubs hatch.

But this was not the main threat to the new species. Observations have shown that "ghost" octopuses are accustomed to laying eggs on dead sponges - these are deep-sea multicellular organisms leading an attached lifestyle. Near the Hawaiian Islands, where Casper was first seen, these sponges are attached to deposits of ferromanganese nodules - formations that include a large number of precious metals (manganese, copper and nickel), which are used, for example, in the manufacture of mobile phones.

Areas of the ocean floor covered with such deposits. In this regard, the territory for breeding octopuses is under threat.

Casper's relatives are recognized as long-lived, which means that if the concretions and sponges living on them disappear completely, it will be almost impossible to restore the "ghostly" octopus population. According to scientists, if this region is used in industrial purposes, the local fauna will not recover even 26 years later. This, in turn, will harm the ecosystem as a whole, as octopuses feed on small organisms, whose populations will increase unpredictably when the former disappear.

Scientists suggest that octopuses prefer to lay eggs on sponges near manganese deposits due to the connection with the source of food, and also because of the safety of such locations (from the point of view of the daily life of the ocean), but this is only a hypothesis that needs to be tested.

So far, very little is known about "ghostly" octopuses, and marine biologists intend to protect the ecosystem and rare view from extinction, because further study of it can provide valuable information. In addition, many more can live at great depths unknown creatures, which will also be affected by anthropogenic activities.

Class Cephalopoda

Cephalopods are the most highly organized molluscs. They are rightly called the "primates" of the sea among invertebrates for the perfection of their adaptations to life in the marine environment and the complexity of their behavior. These are mainly large predatory marine animals that are able to actively swim in the water column. These include squid, octopus, cuttlefish, nautilus (Fig. 234). Their body consists of a torso and head, and the leg is transformed into tentacles located on the head around the mouth, and a special motor funnel on the ventral side of the body (Fig. 234, A). Hence the name - cephalopods. It has been proved that part of the tentacles of cephalopods is formed due to the head appendages.

In most modern cephalopods, the shell is absent or rudimentary. Only the genus Nautilus (Nautilus) has a spirally twisted shell, divided into chambers (Fig. 235).

Only 650 species belong to modern cephalopods, and there are about 11 thousand fossil species. This is an ancient group of mollusks known from the Cambrian. Extinct species of cephalopods were predominantly testate and had an external or internal shell (Fig. 236).

Cephalopods are characterized by many progressive features of organization in connection with actively life marine predators. However, they retain some primitive features that testify to their ancient origin.

External structure. Peculiarities external structure cephalopods are diverse due to different lifestyles. Their sizes range from a few centimeters to 18 m in some squids. Nektonic cephalopods are usually torpedo-shaped (most squids), benthic cephalopods are bag-shaped (many octopuses), nektobenthic are flattened (cuttlefish). Planktonic species are small in size, have a gelatinous buoyant body. The body shape of planktonic cephalopods can be narrow or similar to jellyfish, and sometimes spherical (squid, octopus). Benthopelagic cephalopods have a shell divided into chambers.

The body of a cephalopod consists of a head and a body. The leg is modified into tentacles and a funnel. On the head is a mouth surrounded by tentacles, and large eyes. The tentacles are formed by the head appendages and the leg. These are food trapping organs. The primitive cephalopod - boat (Nautilus) has an indefinite number of tentacles (about 90); they are smooth, worm-like. In higher cephalopods, the tentacles are long, with powerful muscles and carry large suckers on inner surface. The number of tentacles is 8-10. Cephalopods with 10 tentacles have two tentacles - trapping, longer, with suckers at widened ends,

Rice. 234. Cephalopods: A - nautilus Nautilus, B - octopus Benthoctopus; 1 - tentacles, 2 - funnel, 3 - hood, 4 - eye

Rice. 235. Nautilus Nautilus pompilius with a sawn shell (according to Owen): 1 - head hood, 2 - tentacles, 3 - funnel, 4 - eye, 5 - mantle, 6 - visceral sac, 7 - chambers, 8 - partition between shell chambers, 9 - siphon

Rice. 236. Scheme of the structure of cephalopod shells in sagittal section (from Gescheler): A - Sepia, B - Belosepia, C - Belemnites, D - Spirulirostra, E - Spirula, E - Ostracoteuthis, G - Ommastrephes, H - Loligopsis (C, D, E - fossils); 1 - proostracum, 2 - dorsal edge of the siphon tube, 3 - ventral edge of the siphon tube, 4 - collection of phragmocone chambers, 5 - rostrum, 6 - siphon cavity

and the remaining eight tentacles are shorter (squid, cuttlefish). The octopuses living on seabed, eight tentacles of the same length. They serve the octopus not only to capture food, but also to move along the bottom. In male octopuses, one tentacle is modified into a sexual (hectocotyl) and serves to transfer the reproductive products into the mantle cavity of the female.

Funnel - a derivative of the leg in cephalopods, serves for a "reactive" way of movement. Through the funnel, water is forcefully pushed out of the mantle cavity of the mollusk, and its body moves reactively in the opposite direction. At the boat, the funnel has not grown together on the ventral side and resembles the sole of the foot of crawling mollusks rolled into a tube. The proof that the tentacles and funnel of cephalopods are leg derivatives is their innervation from the pedal ganglia and the embryonic anlage of these organs on the ventral side of the embryo. But, as already noted, some of the tentacles of cephalopods are derivatives of the head appendages.

The mantle on the ventral side forms, as it were, a pocket - a mantle cavity that opens outwards with a transverse slit (Fig. 237). A funnel protrudes from this gap. On the inner surface of the mantle there are cartilaginous protrusions - cufflinks, which fit tightly into the cartilaginous recesses on the body of the mollusk, and the mantle is, as it were, fastened to the body.

The mantle cavity and funnel together provide jet propulsion. When the muscles of the mantle relax, water enters through the gap into the mantle cavity, and when it contracts, the cavity closes with cufflinks and the water is pushed out through the funnel. The funnel is able to bend to the right, to the left and even back, which provides a different direction of movement. The role of the steering wheel is additionally performed by tentacles and fins - the skin folds of the body. Types of movement in cephalopods are diverse. Octopuses often move on tentacles and rarely swim. In cuttlefish, in addition to the funnel, a circular fin serves for movement. Some deep-sea umbrella-shaped octopuses have a membrane between the tentacles - umbrella and can move due to its contractions, like jellyfish.

The shell in modern cephalopods is rudimentary or absent. In ancient extinct cephalopods, the shell was well developed. Only one extant genus, Nautilus, has retained a developed shell. The shell of Nautilus in fossil forms also has significant morphological and functional features, in contrast to the shells of other mollusks. This is not only a protective device, but also a hydrostatic apparatus. The nautilus has a spirally twisted shell divided by partitions into chambers. The body of the mollusk is located only in the last chamber, which opens outwards with the mouth. The remaining chambers are filled with gas and chamber fluid, which ensures the buoyancy of the body of the mollusk. Through

holes in the partitions between the chambers of the shell passes the siphon - the posterior process of the body. Siphon cells are able to release gases. When surfacing, the mollusk emits gases, displacing the chamber fluid from the chambers; when lowering to the bottom, the mollusk fills the shell chambers with chamber fluid. The mover of the nautilus is a funnel, and the shell maintains its body in suspension in the water. Fossil nautilids had a shell similar to that of the modern nautilus. Completely extinct cephalopods - ammonites also had an external, spirally twisted shell with chambers, but their partitions between the chambers had a wavy structure, which increased the strength of the shell. That is why ammonites could reach very large sizes, up to 2 m in diameter. In another group of extinct cephalopods, the belemnites (Belemnoidea), the shell was internal, overgrown with skin. Belemnites in appearance resembled shellless squids, but in their body there was a conical shell, divided into chambers. The top of the shell ended with a point - the rostrum. Rostrums of belemnite shells are often found in Cretaceous deposits and are called "devil's fingers". Some modern shellless cephalopods have rudiments of the inner shell. Thus, in cuttlefish, a calcareous plate is preserved on the back under the skin, which has a chamber structure on the cut (238, B). Only in spirula (Spirula) under the skin is a fully developed spirally twisted shell (Fig. 238, A), and in squid under the skin only a horny plate has survived from the shell. In females of modern cephalopods - argonauts (Argonauta), a brood chamber is developed, resembling a spiral shell in shape. But this is only a superficial resemblance. The brood chamber is distinguished by the epithelium of the tentacles, is very thin and is designed to protect the developing eggs.

covers. The skin is represented by a single layer of epithelium and a layer of connective tissue. The skin contains pigment cells called chromatophores. Cephalopods are characterized by the ability to quickly change color. This mechanism is controlled nervous system and is carried out by changing the form

Rice. 238. Rudiments of a shell in cephalopods (according to Natalie and Dogel): A - spirula (Spirula); 1 - funnel, 2 - mantle cavity, 3 - anus, 4 - excretory opening, 5 - luminous organ, 6 - fin, 7 - shell, 8 - siphon; B - Sepia shell; 1 - septa, 2 - lateral margin, 3 - siphon fossa, 4 - rostrum, 5 - rudiment of siphon, 6 - posterior margin of proostracum

pigment cells. So, for example, cuttlefish, swimming over sandy ground, takes on a light color, and over rocky ground - dark. .At the same time, pigment cells with dark and light pigment in her skin alternately contract and expand. If you cut the optic nerves of a mollusk, then it loses its ability to change color. Due to the connective tissue of the skin, cartilage is formed: in cufflinks, the bases of the tentacles, around the brain.

Protective devices. Cephalopods, having lost the shell in the process of evolution, acquired other protective devices. Firstly, fast movement saves many of them from predators. In addition, they can defend themselves with tentacles and a "beak", which is a modified jaw. Large squids and octopuses can fight with large marine animals, such as sperm whales. Sedentary and small forms have developed protective coloration and the ability to quickly change color. And finally, some cephalopods, such as cuttlefish, have an ink sac, the duct of which opens into the hindgut. Spraying the ink liquid into the water causes a kind of smoke screen that allows the mollusk to hide from predators to a safe place. Cuttlefish ink gland pigment is used to make high-quality artistic ink.

The internal structure of cephalopods

Digestive system cephalopods bear the features of specialization in feeding on animal food (Fig. 239). They feed mainly on fish, crabs and bivalves. They seize prey with tentacles and kill with jaws and poison. Despite their large size, cephalopods can only eat liquid food, as they have a very narrow esophagus that passes through the brain, enclosed in a cartilaginous capsule. Cephalopods have adaptations for grinding food. To gnaw their prey, they use hard horny jaws, similar to the beak of a parrot. In the pharynx, food is rubbed by the radula and abundantly moistened with saliva. The ducts of 1-2 pairs of salivary glands flow into the pharynx, which secrete enzymes that break down proteins and polysaccharides. The second posterior pair of salivary glands secretes poison. Liquid food from the pharynx through the narrow esophagus enters the endodermal stomach, where the ducts of the steam liver flow, which produces a variety of digestive enzymes. The hepatic ducts are lined with small additional glands, the totality of which is called the pancreas. The enzymes of this gland act on polysaccharides,

and hence this gland is functionally distinct from the mammalian pancreas. The stomach of cephalopods is usually with a blind saccular process, which increases its volume, which allows them to absorb a large portion of food. Like other predatory animals, they eat a lot and relatively rarely. The small midgut departs from the stomach, which then passes into the hind intestine, which opens with an anus into the mantle cavity. In many cephalopods, the duct of the ink gland flows into the hindgut, the secret of which has a protective value.

Nervous system cephalopods is the most highly developed among molluscs. The nerve ganglia form a large peripharyngeal cluster - the brain (Fig. 240), enclosed in a cartilaginous capsule. There are additional ganglia. The composition of the brain primarily includes: a pair of large cerebral ganglia that innervate the head, and a pair of visceral ganglia that send nerve cords to the internal organs. On the sides of the cerebral ganglia are additional large optic ganglia that innervate the eyes. Long nerves depart from the visceral ganglia to two stellate mantle ganglia, which develop in cephalopods in connection with the function of the mantle in their jet mode of movement. The composition of the brain of cephalopods includes, in addition to cerebral and visceral pedal ganglia, which are subdivided into paired ganglia of tentacles (brachial) and funnels (infudibular). The primitive nervous system, similar to the ladder system of lateral nerves and monoplacophorans, is preserved only in Nautilus. It is represented by nerve cords forming a peripharyngeal ring without ganglia and a pedal arch. Nerve cords are covered with nerve cells. This structure of the nervous system indicates the ancient origin of cephalopods from primitive shell mollusks.

sense organs cephalopods are well developed. Their eyes, which are of the greatest importance for orientation in space and hunting for prey, reach a particularly complex development. In Nautilus, the eyes have a simple structure in the form of a deep eye fossa (Fig. 241, A), while in other cephalopods, the eyes are complex - in the form of an eye bubble and resemble the structure of the eye in mammals. This is an interesting example of convergence between invertebrates and vertebrates. Figure 241, B shows the eye of a cuttlefish. From above, the eyeball is covered with the cornea, in which there is an opening into the anterior chamber of the eye. The connection between the anterior cavity of the eye and external environment protects the eyes of cephalopods high pressure at great depths. The iris forms an opening - the pupil. Light through the pupil enters the spherical lens formed by the epithelial body - the upper shell of the eye bubble. The accommodation of the eye in cephalopods is different,

Rice. 240. Nervous system of cephalopods: 1 - brain, 2 - optic ganglia, 3 - mantle ganglia, 4 - intestinal ganglion, 5 - nerve cords in tentacles

than in mammals: not by changing the curvature of the lens, but by approaching or moving away from the retina (similar to focusing a camera). Special ciliary muscles approach the lens, setting it in motion. The cavity of the eyeball is filled with a vitreous body, which has a light-refracting function. The bottom of the eye is lined with visual - retinal and pigment - cells. This is the retina of the eye. A short optic nerve departs from it to the optic ganglion. The eyes, together with the optic ganglia, are surrounded by a cartilaginous capsule. Deep-sea cephalopods have luminous organs on their bodies, built according to the type of eyes.

Organs of balance- Statocysts are located in the cartilaginous capsule of the brain. The organs of smell are represented by olfactory pits under the eyes or osphradia typical of mollusks at the base of the gills - in nautilus. The organs of taste are concentrated on the inner side of the ends of the tentacles. Octopuses, for example, use their tentacles to distinguish between edible and inedible objects. On the skin of cephalopods, there are many tactile and light-sensitive cells. In search of prey, they are guided by a combination of visual, tactile and taste sensations.

Respiratory system represented by ctenidia. Most modern cephalopods have two, while the nautilus has four. They are located in the mantle cavity on the sides of the body. The flow of water in the mantle cavity, which ensures gas exchange, is determined by the rhythmic contraction of the muscles of the mantle and the function of the funnel through which water is pushed out. During the jet mode of movement, the flow of water in the mantle cavity accelerates, and the intensity of respiration increases.

Circulatory system cephalopods almost closed (Fig. 242). In connection with active movement, they have well-developed coelom and blood vessels and, accordingly, parenchymality is poorly expressed. Unlike other mollusks, they do not suffer from hypokenia - poor mobility. The speed of blood movement in them is ensured by the work of a well-developed heart, consisting of a ventricle and two (or four - in Nautilus) atria, as well as pulsating sections of blood vessels. The heart is surrounded by a large pericardial cavity

which performs many functions of the whole. From the ventricle of the heart depart the head aorta - forward and splanchnic aorta - back. The head aorta branches into arteries that supply blood to the head and tentacles. Vessels depart from the splanchnic aorta to the internal organs. Blood from the head and internal organs is collected in the vena cava, located longitudinally in the lower part of the body. The vena cava subdivides into two (or four in Nautilus) afferent gill vessels, which form contracting extensions - gill "hearts" that promote gill blood circulation. The afferent gill vessels lie close to the kidneys, forming small blind protrusions into the tissue of the kidneys, which contributes to the release of venous blood from metabolic products. In the gill capillaries, blood is oxidized, which then enters the efferent gill vessels, which flow into the atria. Partially, blood from the capillaries of veins and arteries flows into small gaps, and therefore circulatory system cephalopods should be considered almost closed. The blood of cephalopods contains a respiratory pigment - hemocyanin, which includes copper, therefore, when oxidized, the blood turns blue.

excretory system represented by two or four (in Nautilus) kidneys. With their inner ends they open into the pericardial sac (pericardium), and with their outer ends into the mantle cavity. Excretion products enter the kidneys from the gill veins and from the extensive pericardial cavity. Additionally, the excretory function is performed by the pericardial glands formed by the wall of the pericardium.

Reproductive system, reproduction and development. Cephalopods are dioecious animals. In some species, sexual dimorphism is well expressed, for example, in the argonaut (Argonauta). The female argonaut is larger than the male (Fig. 243) and during the breeding season she secretes a thin-walled parchment-like brood chamber around the body with the help of special glands on the tentacles for carrying eggs, similar to a spiral shell. The male argonaut is several times smaller than the female and has a special elongated sexual tentacle, which is filled during the breeding season with sexual products.

Gonads and genital ducts unpaired. An exception is the nautilus, which has preserved paired ducts extending from the unpaired gonad. In males, the vas deferens passes into the spermatophore bag, where the spermatozoa stick together into special packages - spermatophores. In cuttlefish, the spermatophore is shaped like a checker; its cavity is filled with spermatozoa, and the outlet is closed with a complex plug. During the breeding season, the male cuttlefish, with the help of a sexual tentacle with a spoon-shaped end, transfers the spermatophore into the mantle cavity of the female.

Cephalopods usually lay their eggs at the bottom. In some species, care for offspring is observed. So, the female argonaut bears eggs in the brood chamber, and the octopuses guard the clutch of eggs, which are placed in shelters made of stones or in caves. Development is direct, without metamorphosis. The eggs hatch into small, fully formed cephalopods.

Modern cephalopods belong to two subclasses: the subclass Nautilida (Nautiloidea) and the subclass Coleoidea (Coleoidea). Extinct subclasses include: subclass Ammonites (Ammonoidea), subclass Bactrites (Bactritoidea) and subclass Belemnites (Belemnoidea).

Subclass Nautilida (Nautiloidea)

Modern nautilids include one order Nautilida. It is represented by only one genus Nautilus, to which only a few species belong. The distribution area of ​​Nautilus is limited to the tropical regions of the Indian and Pacific Oceans. Fossil nautilids number over 2,500 species. This is an ancient group of cephalopods known from the Cambrian.

Nautilids have many primitive features: the presence of an external multi-chambered shell, an unfused funnel, numerous tentacles without suckers, and manifestation of metamerism (four ctenidia, four kidneys, four atria). The similarity of nautilids with lower shell molluscs is manifested in the structure of the nervous system from cords without isolated ganglia, as well as in the structure of coelomoducts.

Nautilus is a benthopelagic cephalopod. It floats in the water column in a "reactive" way, pushing the water out of the funnel. The multi-chamber shell provides buoyancy of its body and lowering to the bottom. Nautilus has long been an object of fishing because of the beautiful mother-of-pearl shell. Nautilus shells have been used to make many fine jewelry pieces.

Subclass Coleoidea (Coleoidea)

Coleoidea is Latin for "hard". These are hard-skinned molluscs without a shell. Coleoidea is a thriving group of modern cephalopods, includes four orders, which include about 650 species.

Common features of the subclass are: lack of a developed shell, fused funnel, tentacles with suckers.

Unlike nautilids, they have only two ctenidia, two kidneys, and two atria. Coleoidea have a highly developed nervous system and sensory organs. The following three orders are characterized by the largest number of species.

Squad Cuttlefish (Sepiida). The most characteristic representatives of the order are cuttlefish (Sepia) and spirula (Spirula) with rudiments of the inner shell. They have 10 tentacles, two of which are agility. These are nektobenthic animals, they stay at the bottom and are able to actively swim.

Order Squid (Teuthida). This includes many commercial squids: Todarodes, Loligo, etc. Squids sometimes retain a rudiment

shells in the form of a horny plate under the skin on the back. They have 10 tentacles, like the previous unit. These are mainly nektonic animals that actively swim in the water column and have a torpedo-shaped body (Fig. 244).

Order Octopus (Octopoda). This is an evolutionarily advanced group of cephalopods without traces of a shell. They have eight tentacles. Sexual dimorphism is pronounced. Males develop a sexual tentacle - hectocotylus. This includes a variety of octopuses (Fig. 245). Most octopuses lead a benthic lifestyle. But among them there are nektonic and even planktonic forms. The Octopoda order includes the genus Argonauta - an argonaut, in which the female allocates a special brood chamber.

The practical importance of cephalopods

Cephalopods are food animals. The meat of cuttlefish, squid and octopus is used for food. The world catch of cephalopods currently reaches more than 1600 thousand tons. in year. Cuttlefish and some octopuses are also harvested for ink liquid, which is used to make natural ink and top quality inks.

Paleontology and phylogeny of cephalopods

The most ancient group of cephalopods is considered to be nautilids, whose fossil shells are already known from Cambrian deposits. Primitive nautilids had a low conical shell with only a few chambers and a wide siphon. Cephalopods are thought to have evolved from ancient, creeping shellfish with simple conical shells and flat soles like some fossil monoplacophorans. Apparently, a significant aromorphosis in the emergence of cephalopods consisted in the appearance of the first partitions and chambers in the shell, which marked the beginning of the development of their hydrostatic apparatus and determined the possibility of floating up, breaking away from the bottom. Apparently, the formation of a funnel and tentacles occurred in parallel. The shells of the ancient nautilids were varied in shape: long conical and flat spirally twisted with a different number of chambers. Among them there were also giants up to 4-5 m (Endoceras), which led a benthic lifestyle. Nautilids have undergone in the process historical development several periods of prosperity and extinction have existed to this day, although they are now represented by only one genus of Nautilus.

In the Devonian, in parallel with the nautilids, it begins to occur special group cephalopods - bactrites (Bactritoidea), smaller in size and less specialized than nautilids. It is assumed that this group of cephalopods descended from a common yet unknown ancestors with nautilids. Bactrites turned out to be evolutionarily promising group. They gave rise to two branches of cephalopod development: ammonites and belemnites.

A subclass of ammonites (Ammonoidea) appeared in the Devonian and died out at the end of the Cretaceous. During their heyday, ammonites successfully competed with nautilids, whose numbers at that time were noticeably declining. It is difficult for us to judge the advantages of the internal organization of ammonites only from fossil shells. But the ammonite shell was more perfect,

Rice. 246. Fossil cephalopods: A - ammonite, B - belemnite

than nautilids: lighter and stronger. The partitions between the chambers in ammonites were not smooth, but wavy, and the lines of the partitions on the shell were zigzag, which increased the strength of the shell. Ammonite shells were spirally twisted. More often, whorls of ammonite shell spirals were located in the same plane, and less often they had the form of a turbospiral (Fig. 246, A). According to some imprints of the body of ammonite fossils, it can be assumed that they had up to 10 tentacles, perhaps there were two ctenidia, beak-shaped jaws, and an ink bag. This indicates that the ammonites apparently experienced oligomerization of metameric organs. According to paleontological data, ammonites were ecologically more diverse than nautilids, and included nektonic, benthic, and planktonic forms. Most ammonites were small, but there were also giants with a shell diameter of up to 2 m. Ammonites were one of the most numerous marine animals in the Mesozoic, and their fossil shells serve as guiding forms in geology for determining the age of the layers.

Another branch of cephalopod evolution, hypothetically derived from bactrites, was represented by a subclass of belemnites (Belemnoidea). Belemnites appeared in the Triassic, flourished in Cretaceous and became extinct at the beginning of the Cenozoic era. In their external appearance, they are already closer to the modern subclass Coleoidea. In body shape, they resemble modern squids (Fig. 246, B). However, belemnites differed significantly from them in the presence of a heavy shell, which was overgrown with a mantle. The shell of belemnites was conical, multi-chambered, covered with skin. Remains of shells and especially their terminal finger-like rostrums, which are figuratively called "devil's fingers", have been preserved in geological deposits. Belemnites were often very large: their length reached several meters. The extinction of ammonites and belemnites was probably due to increased competition with bony fish. And now, in the Cenozoic, a new group of cephalopods enters the arena of life - coleoids (subclass Coleoidea), devoid of shells, with fast jet propulsion, with a sophisticated nervous system and sensory organs. It was they who became the "primates" of the sea and could compete on equal terms as predators with fish. This group of cephalopods appeared

in the Cretaceous, but reached its highest peak in Cenozoic era. There is reason to believe that the Coleoidea have common origins with the Belemnites.

Ecological radiation of cephalopods. The ecological radiation of cephalopods is shown in Figure 247. From primitive testate benthopelagic forms capable of surfacing thanks to the hydrostatic apparatus, several paths of ecological specialization have been determined. The most ancient ecological directions were associated with radiation of nautilids and ammonites, which swam at different depths and formed specialized shell forms of benthopelagic cephalopods. From benthopelagic forms, there is a transition to bentonekton (such as belemnites). Their shell becomes internal, and its function of the swimming apparatus weakens. Instead, they develop the main mover - a funnel. Later they gave rise to shellless forms. The latter undergo intense ecological radiation, having formed nektobenthic, nektonic, benthic, and planktonic forms.

The main representatives of the nekton are squids, but there are also fast-swimming octopuses and cuttlefish with a narrow torpedo-shaped body. The composition of the nektobenthos mainly includes cuttlefish, often swimming

or lying on the bottom, to bentonekton - octopuses that crawl along the bottom more than swim. Plankton include umbellate, or gelatinous, octopuses, rod-shaped squids.