The circulatory system of cephalopods briefly. Reproduction of cephalopods

With about 130,000 species, molluscs are second only to arthropods in number of species and represent the second largest phylum of the animal kingdom. Mollusks are predominantly aquatic inhabitants; only a small number of species live on land.

Mollusks have a variety of practical meanings. Among them there are useful ones, such as pearl mussel and mother-of-pearl, which are mined to obtain natural pearls and mother-of-pearl. Oysters and some other species are harvested and even farmed for food. Some species are pests of agricultural crops. From a medical point of view, mollusks are of interest as intermediate hosts of helminths.

General characteristics of the type

Animals belonging to the mollusc type are characterized by:

• three-layer, - i.e. formation of organs from ecto-, ento- and mesoderm
• bilateral symmetry, often distorted due to displacement of organs
• unsegmented body, usually covered by a shell, whole, bivalve or consisting of several plates
• skin fold - a mantle that fits the entire body
• muscular growth - a leg that serves for movement
• poorly defined coelomic cavity
• presence of basic systems: movement apparatus, digestive, respiratory, excretory, circulatory systems, nervous and reproductive systems

The body of mollusks has bilateral symmetry; in gastropods (which includes, for example, the pond snail) it is asymmetrical. Only the most primitive mollusks retain signs of segmentation of the body and internal organs; in most species it is not divided into segments. The body cavity is secondary, presented in the form of a pericardial sac and a cavity of the gonads. The space between the organs is filled with connective tissue (parenchyma).

The body of mollusks consists of three sections - head, trunk and legs. In bivalves, the head is reduced. The leg, a muscular outgrowth of the abdominal wall of the body, is used for movement.

At the base of the body, a large fold of skin is developed - the mantle. Between the mantle and the body there is a mantle cavity in which there are gills, sensory organs, and the openings of the hindgut, excretory and reproductive systems open here. The mantle secretes a shell that protects the body from the outside. The shell can be solid, bivalve, or consist of several plates. The shell contains calcium carbonate (CaCO 3) and the organic substance conchiolin. In many mollusks the shell is more or less reduced (for example, in some cephalopods, in naked slugs, etc.).

The circulatory system is not closed. The respiratory organs are represented by gills or lungs formed by part of the mantle (for example, in pond snails, grape and garden snails, naked slugs). The excretory organs - the kidneys - are connected at their internal ends to the pericardial sac.

The nervous system consists of several pairs of nerve ganglia, interconnected by longitudinal trunks.

The phylum of mollusks includes 7 classes. The most important of them:

• gastropods (Gastropoda) - slow crawling snails
• bivalves (Bivalvia) - relatively sedentary mollusks
• cephalopods (Cephalopoda) - mobile mollusks

Class Gastropoda

This class includes mollusks that have a shell (snails). Its height ranges from 0.5 mm to 70 cm. Most often, the shell of gastropods has the form of a cap or spiral; only representatives of one family develop a shell of 2 valves connected by an elastic ligament. The structure and shape of the shell are of great importance in the taxonomy of mollusks [show] .

1. Placospiral shell - a strongly twisted shell, the whorls of which are located in the same plane
2. Turbo-spiral shell – the revolutions of the shell lie in different planes
3. Right-handed shell - the spiral of the shell twists clockwise
4. Left-handed shell - the spiral twists counterclockwise
5. Cryptospiral (involute) shell - the last whorl of the shell is very wide and completely covers all previous ones
6. Open spiral (evolute) shell – all whorls of the shell are visible

Sometimes the shell is equipped with a lid located on the dorsal side at the back of the leg (for example, in lawns). When you pull your leg into the sink, the lid tightly covers the mouth.

In some species that have switched to a swimming lifestyle (for example, pteropods and keelenopods), there is no shell. Shell reduction is also characteristic of some land gastropods living in the soil and forest litter (for example, slugs).

The body of gastropods consists of a well-separated head, legs and torso - an internal sac; the latter is placed inside the sink. On the head there is a mouth, two tentacles and at their base two eyes.

Digestive system. At the front end of the head is the mouth. It has a powerful tongue covered with a hard chitinous grater, or radula. With its help, mollusks scrape algae from the ground or aquatic plants. In predatory species, a long proboscis develops in the front part of the body, capable of turning out through an opening on the lower surface of the head. In some gastropods (e.g., cones), individual teeth of the radula can protrude from the mouth opening and are shaped like stylets or hollow harpoons. With their help, the mollusk injects poison into the victim’s body. Some predatory gastropod species feed on bivalves. They drill into their shells, secreting saliva containing sulfuric acid.

Through the esophagus, food enters the pouch-shaped stomach, into which the liver ducts flow. Then the food enters the intestine, which bends in a loop and ends on the right side of the body with the anus - the anus.

The nerve ganglia are collected in the peripharyngeal nerve ring, from which nerves extend to all organs. The tentacles contain tactile receptors and chemical sense organs (taste and smell). There are organs of balance and eyes.

In most gastropods, the body protrudes above the leg in the form of a large spirally twisted sac. On the outside it is covered with a mantle and fits closely to the inner surface of the shell.

The respiratory organs of mollusks are represented by gills located in the front part of the body and directed with their apex forward (prosobranchial mollusks) or located in the right rear part of the body and directed with their apex backward (opisthobranchial). In some gastropods (for example, nudibranchs), true gills were reduced. They develop so-called respiratory organs. cutaneous adaptive gills. In addition, in terrestrial and secondary aquatic gastropods, part of the mantle forms a kind of lung, numerous blood vessels develop in its walls, and gas exchange occurs here. The pond snail, for example, breathes atmospheric oxygen, so it often rises to the surface of the water and opens a round breathing hole on the right at the base of the shell. Next to the lung is the heart, which consists of an atrium and a ventricle. The circulatory system is not closed, the blood is colorless. The excretory organs are represented by one kidney.

Among gastropods there are both dioecious species and hermaphrodites, the gonads of which produce both spermine and eggs. Fertilization is always cross-fertilization, development, as a rule, with metamorphosis. Direct development is observed in all land, freshwater and some marine gastropods. Eggs are laid in long mucous threads attached to movable objects.

Belongs to the class of gastropods

• The common pond snail is often found on aquatic plants in ponds, lakes and rivers. Its shell is solid, 4-7 cm long, spirally twisted, with 4-5 curls, a sharp apex and a large opening - the mouth. A leg and head can protrude through the mouth.

  Gastropods also include intermediate hosts of trematodes.

• The intermediate host of the cat fluke, Bithynia leachi, is widespread in freshwater bodies of our country. It lives in the coastal zone of rivers, lakes and ponds overgrown with vegetation. The shell is dark brown and has 5 convex whorls. Shell height 6-12 mm.
• The intermediate host of the liver fluke, the small pond snail (Limnea truncatula), is widespread in Russia. The shell is small, no more than 10 mm in height, forms 6-7 whorls. It lives in ponds, swamps, ditches and puddles, where it is often found in huge quantities. In some areas there are more than 1 million pond snails per hectare of swamps. When swamps dry out, pond snails burrow into the ground, surviving the dry time in the ground.
• The intermediate hosts of the lancet fluke are the terrestrial mollusks Helicella and Zebrina. Distributed in Ukraine, Moldova, Crimea and the Caucasus. Adapted to life in arid conditions; live in the open steppe on the stems of herbaceous plants. During hot weather, helicella often accumulate on plants in clusters, thus saving themselves from drying out. Helicella has a low-conical shell with 4-6 whorls; the shell is light, with dark spiral stripes and a wide rounded mouth. Zebrina has a highly conical shell with 8-11 whorls; the shell is light, with brown stripes running from the top to the base; the mouth is irregularly oval.

Class bivalve (Bivalvia)

This class includes mollusks with a shell consisting of two symmetrical halves, or valves. These are sedentary, sometimes completely motionless animals that live on the bottom of seas and freshwater bodies. They often burrow into the ground. The head is reduced. In freshwater reservoirs, toothless or pearl barley are widespread. Of the marine forms, oysters are the most important. Very large species are found in tropical seas. The shell of a giant tridacna weighs up to 250 kg.

Perlovitsa, or toothless lives on the silted and sandy bottoms of rivers, lakes and ponds. This inactive animal feeds passively. The toothless food consists of detritus particles suspended in water (the smallest remains of plants and animals), bacteria, unicellular algae, flagellates, and ciliates. The mollusk filters them from the water passing through the mantle cavity.

The body of the toothless fish, up to 20 cm long, is covered on the outside with a bivalve shell. There is an expanded and rounded front end of the shell, and a narrowed, pointed rear end. On the dorsal side, the valves are connected by a strong elastic ligament, which maintains them in a semi-open state. The shell closes under the action of two closing muscles - anterior and posterior - each of which is attached to both valves.

There are three layers in the shell - horny, or conchiolin, which gives it a brownish-green color on the outside, a middle thick porcelain-like layer (consists of prisms of carbonated lime; located perpendicular to the surface - the shell) and an inner mother-of-pearl layer (between the thinnest calcareous leaves there are thin layers of conchiolin). The nacreous layer is underlain on each of the two valves by a yellowish-pink fold of the mantle. The epithelium of the mantle secretes the shell, and in some species of freshwater and sea pearl oysters it also forms pearls.

The body is located in the dorsal part of the shell, and a muscular outgrowth extends from it - the leg. In the mantle cavity on both sides of the body there are a pair of lamellar gills.

In the rear part, both shell valves and mantle folds do not fit tightly to one another; two openings remain between them - siphons. The lower inlet siphon serves to introduce water into the mantle cavity. A continuous directed flow of water is carried out due to the movement of numerous cilia that cover the surface of the body, mantle, gills and other organs of the mantle cavity. Water washes the gills and provides gas exchange; it also contains food particles. Through the upper, outlet siphon, used water along with excrement is discharged outside.

The mouth is located at the front end of the body above the base of the leg. On the sides of the mouth there are two pairs of triangular oral lobes. The cilia covering them move food particles toward the mouth. Due to the reduction of the head in pearl barley and other bivalves, the pharynx and associated organs (salivary glands, jaws, etc.) are reduced.

The digestive system of pearl barley consists of a short esophagus, a pouch-shaped stomach, a liver, a long loop-shaped midgut and a short hindgut. A sac-like outgrowth opens into the stomach, inside which there is a transparent crystalline stalk. With its help, food is crushed, and the stalk itself gradually dissolves and releases the amylase, lipase and other enzymes contained in it, which ensure the primary processing of food.

The circulatory system is not closed; Colorless blood flows not only through the vessels, but also in the spaces between the organs. Gas exchange occurs in the gill filaments, from there the blood is sent to the efferent gill vessel and then to the corresponding (right or left) atrium, and from it to the azygos ventricle, from which two arterial vessels begin - the anterior and posterior aorta. Thus, in bivalves, the heart consists of two atria and one ventricle. The heart is located in the pericardial sac on the dorsal side of the body.

The excretory organs, or kidneys, look like dark green tubular sacs; they start from the pericardial cavity and open into the mantle cavity.

The nervous system consists of three pairs of nerve ganglia connected by nerve fibers. The sense organs are poorly developed due to the reduction of the head and a sedentary lifestyle.

Class Cephalopoda

unites the most highly organized mollusks leading an active lifestyle. Cephalopods include the largest representatives of invertebrates - octopuses, squids, cuttlefish.

The body shape of cephalopods is very diverse and depends on their lifestyle. Inhabitants of the water column, which include most squids, have an elongated, torpedo-shaped body. Benthic species, among which octopuses predominate, are characterized by a sac-like body. In cuttlefish living in the bottom layer of water, the body is flattened in the dorsoventral direction. Narrow, spherical or jellyfish-like planktonic species of cephalopods are distinguished by their small size and gelatinous body.

Most modern cephalopods do not have an external shell. It turns into an element of the internal skeleton. Only nautiluses retain an outer, spirally twisted shell, divided into internal chambers. In cuttlefish, the shell, as a rule, has the appearance of a large porous calcareous plate. Spirula retains a spirally twisted shell hidden under the skin. In squids, only a thin horny plate is retained from the shell, stretching along the dorsal side of the body. In octopuses, the shell is almost completely reduced and only small crystals of lime carbonate remain. Female argonauts (one of the species of octopuses) develop a special brood chamber, shaped very much like an external shell. However, this is only an apparent similarity, since it is secreted by the epithelium of the tentacles and is intended only to protect developing eggs.

One of the distinguishing features of cephalopods is the presence of an internal cartilaginous skeleton. Cartilage, similar in structure to the cartilage of vertebrates, surrounds the head cluster of ganglia, forming a cartilaginous capsule. Branches extend from it, reinforcing the eye openings and balance organs. In addition, supporting cartilages develop in the cufflinks, base of the tentacles and fins.

The body of cephalopods consists of a head with compound eyes, a crown of tentacles or arms, a funnel and a torso. Large, complex eyes are located on the sides of the head and are not inferior in complexity to the eyes of vertebrates. The eyes have a lens, cornea and iris. Cephalopods have developed not only the ability to see in stronger or weaker light, but also accommodation. True, it is achieved not by changing the curvature of the lens, as in a person, but by bringing it closer or further away from the retina.

On the head around the mouth opening there is a crown of very mobile tentacles, which are one part of a modified leg (hence the name). The vast majority of species have powerful suckers on their inner surface. Squids use tentacles to catch prey; male octopuses use one of the tentacles to carry reproductive products. During the breeding season, this tentacle is modified, and during the mating period it breaks off and, due to its ability to move, penetrates into the mantle cavity of the female.

The other part of the leg turns into a funnel, which plays an important role in movement. It grows to the ventral side of the body, opening at one end into the mantle cavity, and at the other into the external environment. The mantle cavity in cephalopods is located on the ventral side of the body. At the junction of the body and the head, it communicates with the external environment through a transverse abdominal opening. To close it, in most cephalopods, paired semilunar fossae are formed on the ventral side of the body. Opposite them, on the inner side of the mantle, lie two hard tubercles reinforced with cartilage, the so-called. cufflinks As a result of muscle contraction, the cufflinks fit into the semilunar recesses, tightly fastening the robe to the body. When the abdominal opening is open, water freely penetrates into the mantle cavity, washing the gills lying in it. After this, the mantle cavity closes and its muscles contract. The water is forcefully pushed out of the funnel lying between the two cufflinks, and the mollusk, receiving a reverse push, moves forward with the rear end of the body. This method of movement is called reactive.

All cephalopods are predators and feed on a variety of crustaceans and fish. They use tentacles to capture prey, and powerful horny jaws to kill. They are located in the muscular pharynx and resemble the beak of a parrot. The radula is also placed here - a chitinous ribbon with 7-11 rows of denticles. 1 or 2 pairs of salivary glands open into the pharynx. Their secretion contains hydrolytic enzymes that break down polysaccharides and proteins. Often the secretions of the second pair of salivary glands are poisonous. The venom also helps immobilize and kill large prey.

The intestine is branched, with digestive glands. In many species, just before the anus, the duct of the ink gland opens into the lumen of the hindgut. It secretes a dark secretion (ink) that can cloud a large amount of water. The ink serves as a smoke screen, disorienting the enemy, and sometimes paralyzing his sense of smell. Cephalopods use it to escape from predators.

The circulatory system is almost closed. A heart with 2 or 4 atria, also 2 or 4 kidneys, their number is a multiple of the number of gills.

The nervous system has the highest organization with developed structures of touch, smell, vision and hearing. The ganglia of the nervous system form a common nervous mass - a multifunctional brain, which is located in a protective cartilaginous capsule. Two large nerves arise from the posterior part of the brain. Cephalopods have complex behavior, have good memory and exhibit the ability to learn. Because of the perfection of their brains, cephalopods are called “primates of the sea.”

The unique cutaneous photoreceptors of cephalopods respond to the slightest changes in light. Some cephalopods are capable of glowing due to the bioluminescence of photophores.

All cephalopods are dioecious animals; Some of them have well-defined sexual dimorphism. Males, as a rule, are smaller than females, armed with one or two modified arms - hectocotyls, with the help of which "packets" with seminal fluid - spermatophores - are transferred during the copulation period. Fertilization is external-internal and occurs not in the female’s reproductive tract, but in her mantle cavity. It involves the capture of sperm by the gelatinous membrane of the eggs. After fertilization, females attach clusters of eggs to bottom objects. Some species take care of their offspring and protect developing eggs. The female protecting the offspring can starve for more than 2 months. In octopuses, cuttlefish and nautiluses, a minicopy of the parents hatches from each egg, only in squids development occurs with metamorphosis. The young grow quickly and often reach sexual maturity by one year.

The meaning of shellfish

Freshwater pearl mussel shells with a mother-of-pearl layer thickness of about 2.5 mm are suitable for making mother-of-pearl buttons and other jewelry. Some bivalves (mussels, oysters, scallops), grape snail from gastropod mollusks (in some European countries it is bred in snail farms), are consumed as food; among cephalopods, squid is especially valuable in terms of calorie content and protein composition (more than 600 thousand of them are caught annually in the world . T).

River zebra mussels are found in huge quantities in the reservoirs of the Volga, Dnieper, Don, in lakes, estuaries of the Black Sea, and desalinated areas of the Azov, Caspian and Aral seas. It grows over stones, piles and various hydraulic structures: watercourses, technical and drinking water supply pipes, protective gratings, etc., and its quantity can reach 10 thousand copies per 1 m2 and cover the substrate in several layers. This makes it difficult for water to pass through, so constant cleaning of zebra mussel fouling is necessary; use mechanical, chemical, electrical and biological control methods. Some bivalves bore passages in the bottoms of ships and wooden parts of port facilities (shipworm).

Pearl barley and some other bivalves play an important role in marine and freshwater biocenoses as natural water purifiers - biofilters. One large pearl barley can filter 20-40 liters of water per day; mussels inhabiting 1 m2 of the seabed can filter about 280 m3 of water per day. In this case, mollusks extract organic and inorganic substances from contaminated water, some of which are used for their own nutrition, and some are concentrated in the form of lumps that are used to feed microorganisms.

Thus, mollusks are one of the most important parts of the self-purification system of a reservoir. Particularly important in the system of biological self-purification of water bodies are mollusks, which have special mechanisms of resistance to pollution of water bodies with toxic substances and mineral salts, and are also adapted to living in water with a reduced amount of oxygen. The basis of the molecular mechanism of such adaptation are carotenoids contained in the nerve cells of mollusks. Pearl barley and other filter-feeding mollusks need protection. They can be bred in special containers and used to clean artificial reservoirs from pollution, waste disposal and obtain additional food products.

Shellfish fishing is especially important in Japan, the USA, Korea, China, Indonesia, France, Italy, and England. In 1962, the production of mussels, oysters, scallops and other bivalves amounted to 1.7 million tons; by now, natural reserves of valuable edible shellfish have been depleted. In many countries, marine and freshwater mollusks are bred artificially. Since 1971, in the northwestern part of the Black Sea, mussels have been bred in an experimental farm (productivity is 1000 quintals of mussels per year), research on mussel breeding is also carried out in the basins of other seas washing the shores of our country. Shellfish meat is easily digestible, it contains a lot of vitamins, carotenoids, microelements (iodine, iron, zinc, copper, cobalt); it is used as food by the population, as well as for fattening domestic animals. Filter-feeding mollusks can also be used in a biomonitoring system to monitor the chemical composition of water in reservoirs.

Cephalopods, common in all seas except desalinated seas, despite the fact that they are predators, often themselves serve as food for many fish and marine mammals (seals, sperm whales, etc.). Some cephalopods are edible and are subject to commercial fishing. In China, Japan and Korea, the use of these animals as food goes back centuries; in Mediterranean countries it also has a very long history. According to Aristotle and Plutarch, octopuses and cuttlefish were common food in ancient Greece. In addition, they were used in medicine, perfumery and in the manufacture of first-class paints. Currently, innate programs of complex behavior are being studied in the laboratory on cephalopods.

The body of cephalopods is bilaterally symmetrical, divided into a head and a trunk. The leg transformed into tentacles and a funnel. The shell in primitive forms is external, multi-chambered (Nautilus pompilius), while in higher representatives it is internal, reduced, and often absent. On the head there is a mouth surrounded by tentacles and large eyes. The tentacles of most species have suckers.

rice. 1. Octopus structure diagram:
1 - gill, 2 - gill heart, 3 - kidney, 4 - heart,
5 - gonad, 6 - intestines, 7 - stomach,
8,9 - ink sacs, 10 - pancreas,
11 - mantle muscles, 12 - liver, 13 - goiter,
14 - poisonous gland, 15 - skull, 16 - brain,
17 - cephalic vein, 18 - pharyngeal muscles,
19 - nerves of the tentacles, 20 - beak, 21 - funnel.

The integument is represented by a single-layer epithelium and a layer of connective tissue. The skin contains pigment cells - chromatophores, thanks to which cephalopods can quickly change body color.

The anal, genital and excretory openings open into the mantle cavity, located on the abdominal side. To quickly move, cephalopods use a reactive method: with the help of strong muscle contractions, they throw water through a funnel from the mantle cavity, the recoil pushes the body in the opposite direction.

Cephalopods are predators. They feed on fish, crustaceans, mollusks, etc. Prey is grabbed by tentacles and killed with hard horny jaws and poison. The pharynx contains the tongue with a radula. 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. The esophagus passes through the brain, so there should be no large particles in the food gruel. The esophagus is followed by the stomach, small intestine, hindgut, ending in the anus. The ducts of the liver and “pancreas” flow into the stomach. The duct of the “ink sac” opens into the hindgut. Its secretion is released in case of danger through the anus. The “ink” forms a kind of smoke screen in the water, allowing the cephalopod to elude its pursuer.

The respiratory organs are represented by real gills (ctenidia), located in the mantle cavity on the sides of the body.

The circulatory system has a heart, consisting of a ventricle and atria (two or four), in addition there are two so-called “gill hearts”, which, contracting rhythmically, push blood through the gills. Oxidized blood returns to the heart. The blood contains the respiratory pigment hemocyanin, which contains copper. When oxidized, such blood turns blue.

The excretory system consists of two or four kidneys. Their inner ends open into the pericardium, and their outer openings into the mantle cavity.

The nervous system of cephalopods is the most highly organized among all invertebrates. The ganglia form a common peripharyngeal nerve mass protected by a cartilaginous “skull”. The sense of smell is well developed. The organs of vision are represented by large, complexly arranged eyes that are capable of accommodation. Unlike the human eye, accommodation is not accomplished by changing the curvature of the lens, but by bringing the lens closer or further away relative to the retina.

rice. 2. Ammonite
(reconstruction)

rice. 3.
A - shell,
B - appearance
(reconstruction):
1 - rostrum.

Cephalopods are dioecious. Fertilization occurs in the female's mantle cavity. Development is direct. In some species, care for the offspring takes place.

The class Cephalopods is divided into two subclasses: Nautiloidea, Coleoidae.

Cephalopods appeared in the Cambrian period of the Paleozoic era. The first cephalopods had an external straight shell divided into chambers. The length of such shells reached 4-5 m. Ammonites have been known since the Devonian period of the Paleozoic era (Fig. 2). Ammonites had a spirally twisted multi-chambered shell, the whorls of which were in the same plane. The diameter of ammonite shells reached 2 m. In the Cretaceous period of the Mesozoic era, ammonites died out. Ammonites were among the most common animals of the Mesozoic era, and their fossil shells serve as geological guides for determining the age of strata. Belemnites appeared in the Triassic of the Mesozoic era. Their body shape resembled modern squids (Fig. 3). But their inner shell was conical and multi-chambered. The terminal rostrum of their shells, which can be found in geological deposits, are called “devil's fingers.” The body length of some types of belemnites reached several meters. Belemnites were widespread in the Jurassic period of the Mesozoic era and completely died out by the mid-Paleogene of the Cenozoic era. In the Cretaceous period of the Mesozoic era, coleoids appeared, with a complex nervous system and sensory organs, with reactive movement, and with an internal reduced shell. Coleoids are reaching their peak by now.

Description of classes, subclasses and orders of the Mollusc type:

Class Gastropoda

Marine animals, cephalopods, have long ago attracted the attention of sailors and fishermen, travelers and zoological scientists. True and fictitious stories have been told about these unusual animals. Indeed, their body structure, methods of movement, lifestyle and interesting adaptations to living conditions are unusual.

The class of cephalopods includes about 600 species of animals: octopuses, squids, cuttlefish. In appearance, they are completely different from gastropods (snails, slugs) and bivalves (mussels, oysters). As the name suggests, cephalopods are molluscs with a clearly distinct head and a crown of eight (in octopuses) or ten (in squid and cuttlefish) tentacles surrounding the mouth. Tentacles are muscular organs equipped with suction cups, and sometimes also with horny hooks, used for movement and obtaining food. For example, an octopus walks along the bottom on them like on stilts. Along with this, the tentacles also serve as organs for grasping and holding prey. Science has established that the tentacles of cephalopods correspond to the modified and dismembered legs of other mollusks.

Yes, neither the octopus, nor the cuttlefish, nor the squid are similar to the grape snail or pond snail, rapana or tiger snail. However, they have much in common in their anatomy, physiology, origin and development.

Cephalopods live mainly in tropical and subtropical regions. Off the coast of our country they are found only in the Barents and Far Eastern seas.

Cephalopods have not one, but three hearts: one head, and two gills. And their blood is unusual - blue! Dark blue when saturated with oxygen, and pale when saturated with carbon dioxide. The bluish color of blood depends on the copper it contains.

No other animal has such large eyes as cephalopods. For example, the eye of a cuttlefish is only ten times smaller than its body, and the giant octopus has eyes the size of a wheel with a diameter of up to 40 cm. All cephalopods are predators. Their mouth is small, their throat is muscular and has a black horny beak, reminiscent of an owl's beak. The main food of cephalopods is fish, crabs, and small mollusks.

Of undoubted interest in cephalopods is their reactive movement. The greatest perfection in this method of movement was achieved by squids, capable of reaching speeds of up to 60 km/h. Their body shape even served as a model for designing the shape of rockets. How does the movement of cephalopods occur? It turns out that through the mantle hole, located in the front part of the mollusk’s body, water enters the mantle cavity. Having taken in water, the mollusk tightly clamps the mantle opening and, squeezing the abdominal muscles, forcefully pushes out a stream of water that shoots out of the siphon, as if from a cannon. The resulting reactive force quickly pushes the mollusk in the opposite direction, and it quickly, like a rocket, slides through the water with the back end of its body first!

Cephalopods are aggressive and attack prey, sometimes even several times their size. But they also have many enemies: fish (sharks, moray eels, tuna, mackerel, cod), birds (albatrosses, skuas, penguins), and marine mammals (toothed whales, dolphins and seals).

The highly developed nervous system and sensory organs provide the complex behavior of cephalopods.

However, cephalopods have reliable defense organs. They defend themselves not only with powerful tentacles, but also with their beak. When attacking, they even bite through the hard shells of bivalves. I. A. Akimushkin writes: “Four to six kilogram squid easily bite through the wire line of a spinning rod.” And in case of danger, they are able to instantly use their camouflage or suddenly appearing scaring colors.

In a moment of danger, a squid, cuttlefish or octopus ejects a stream of black liquid from the funnel. This fluid is produced by a special organ - the pear-shaped outgrowth of the rectum - the “ink sac”. The liquid spreads in the water like a thick cloud, and under the cover of a “smoke screen” the mollusk disappears, leaving the enemy completely stunned. After launching the “ink curtain”, the squid takes on a pale body color. “But the most striking thing,” writes I. A. Akimushkin, “is that the shape of the “curtain” seems to resemble the outlines of the animal throwing it out. The enemy is confused." In addition, the “ink liquid” deprives the enemy of the sense of smell and the ability to pursue.

Some squids are very large. Of these, the largest is Architeuthis, up to 18 m long (with elongated tentacles). The torpedo-shaped elongated body of squids determines their high speed.

About 30 species of squid live off the coast of the Russian Federation. They live in the Sea of ​​Okhotsk, Barents and Sea of ​​Japan. These animals spend their entire lives in the water column, chasing schools of herring and other fish.

Cuttlefish's body shape resembles bottom-dwelling fish. Their flattened body and suitable coloring camouflage these mollusks well in a natural environment. They swim slowly, using lateral fins. An interesting representative of cuttlefish is sepia. According to British naturalist Frank Lane, “these animals literally left their mark on human culture,” as for many centuries people wrote with ink extracted from cuttlefish. Natural sepia dye, used in large quantities by industry, is also famous. And in perfumery and medicine, the remnant of the underdeveloped inner shell of this mollusk, the so-called “bone,” is also used.

The typical and largest representative of octopuses is the common octopus, which is also called the common octopus. It lives in tropical seas, but is also found in the Sea of ​​Japan. The octopus builds its shelters from stones and all kinds of objects at the bottom of the sea or occupies ready-made ones.

When an octopus sleeps, it does not close its eyes (only the pupils contract), its breathing slows down, and its body color becomes brownish-gray. The guard tentacles extend upward and slowly circle over the animal. The octopus is sleeping...

The octopus is capable of “purposeful” use of tools. Sometimes he, holding a stone in one of his “hands,” watches the pinna bivalve until it opens its shell, after which the octopus inserts a stone between the valves to prevent the shell from closing. After this, the pinna becomes easy prey for the octopus.

In coastal countries, cephalopods are used as food, producing over a million tons annually. In order to more rationally use these animals, the first octopus reserve was organized in Japan.

Cephalopods are the most unusual, largest and most highly organized of mollusks. A number of unique features - great activity, method and speed of movement, an unusually highly developed nervous system, the beginnings of "intelligence", a set of means of defense and attack - puts cephalopods above all other groups of invertebrates and allows them to compete with vertebrates.

At first glance, cephalopods - octopuses, cuttlefish and squids - do not resemble other mollusks in any way. They (except Nautilus) there is not even a shell, so typical of soft-bodied animals.

Rice. 22. Squid Wonderful lamp Lycoteuthis diadema.

These mollusks received the name “cephalopod” because they have limbs on their heads - tentacles, with the help of which many animals can move along the bottom. In addition, it has been established that the limbs of cephalopods developed from the legs of an ancient ancestor.

The sizes of cephalopods vary greatly. Among them there are dwarfs, whose mantle length is less than 1 cm, and giants, which include squids. The length of their body including tentacles can reach 18 m.

Cephalopods are exclusively marine animals. They play a very important role in ocean life. Being predators, they eat a huge amount of crustaceans, fish and, in turn, themselves serve as food for many marine vertebrates - fish, birds, pinnipeds and whales. The most important enemy of cephalopods is the giant toothed whale - the sperm whale.

Cephalopods are bilaterally symmetrical animals.

In cuttlefish the body is flattened, in squid it is cylindrical, pointed towards the rear end, fusiform, in octopuses it is sac-shaped. In all cephalopods, the body is covered with a skin-muscular sac - a mantle, which encloses the internal organs. On the sides of the mantle of squid, cuttlefish and pelagic octopuses there are fins, which come in a wide variety of shapes and sizes, and serve the mollusks for swimming and as rudders. The head of most cephalopods is large, often somewhat wider than the mantle and separated from it by a cervical interception, but in octopuses the head is fused with the mantle. The head bears eyes, often very large, especially in deep-sea squids, and tentacles that surround the mollusk’s mouth like a crown.

The inner surface of the tentacles (arms) is lined with suction cups. They are located in 1–4 (rarely more) longitudinal rows.

A muscular conical tube is attached to the underside of the head and sometimes grows, with its base extending into the mantle cavity. This funnel, or siphon, the main propulsion device of the cephalopod, its “jet engine”.

The mouth opening of cephalopods is small. The pharynx is muscular, equipped with two strong chitinous jaws, reminiscent of a parrot's beak and called " beak" In the oral cavity on a special tongue-like protrusion - odontophore a radula is placed - a chitinous ribbon seated in rows of small denticles. With the help of the radula, food that enters the mollusk’s mouth and is moistened with saliva is transported further into the esophagus. A thin tube, the esophagus, stretches from the throat to the stomach, piercing the brain and liver on its way to the stomach. Therefore, cephalopods, despite their great appetite, cannot swallow their prey whole, but are forced to crush it into small pieces with their “beak” before putting it in their mouth. The eaten pieces of food then enter the muscular stomach, which receives digestive juices produced by the liver and pancreas. The enzyme activity of these glands is very high, and food is digested within 4 hours. Absorption occurs in the caecum of the stomach - tsekume, as well as in the liver. Undigested food remains enter the intestine and are thrown out.

In the upper part of the mantle cavity there are gills- one on both sides of the visceral mass.

The blood is set in motion three hearts – main consisting of a ventricle and two atria, and two gills. The main heart pumps blood throughout the body, and the rhythmic contractions of the gill hearts push venous blood through the gills, from where it, enriched with oxygen, enters the atrium of the main heart. The heart rate depends on the water temperature. For example, an octopus at a water temperature of 22 °C has a heart rate of 40–50 beats per minute.

Cephalopods have an almost closed circulatory system: in many places (skin, muscles) there are capillaries through which arteries turn into veins.

The blood of cephalopods is blue due to the presence of respiratory pigment. hemocyanin, containing copper. Hemocyanin is produced in special gill glands.

A highly developed circulatory system allows cephalopods to reach gigantic sizes.

The excretory organs are the kidney sacs, the appendages of the gill hearts, and the gills themselves. The main metabolic product of cephalopods is ammonia (more precisely, ammonium ions).

All cephalopods are dioecious. Male cephalopods are usually smaller than females, and when mature, one or two of their arms will change, turning into hectocotylus, with the help of which males transfer spermatophores to the female’s seminal receptacles during copulation.

Spermatophores - “packets” with seminal fluid - are complex and have different shapes in different species. Typically, the spermatophore is a thin, slightly curved tube, shaped like a Cossack saber. Spermatophores are formed in a special section associated with the testis - the spermatophore organ; they accumulate in a special storage facility - the spermatophore sac. During mating, spermatophores emerge through the excretory canal, are picked up by the hectocotylus and transferred to the female's spermatheca. In cuttlefish and some squids, the spermatheca is located on the oral membrane of the female.

The nervous system of cephalopods is more complex than that of other invertebrate animals. In terms of complexity, it is not inferior to the nervous system of fish. The ganglia are very close together and essentially form a single nervous mass - the brain, which in intrashell cephalopods is also enclosed in a cartilaginous capsule - the skull. In terms of relative mass, the brain of cephalopods exceeds that of fish, but is inferior to the brain of birds and mammals.

The brain consists of lobes, the total number of which in an octopus is 64. The optical lobes are the largest of them - they can account for 4/5 of the volume of the brain. In terms of subtlety of feelings, accuracy of perception and complexity of responses and behavior, cephalopods are superior to many marine animals. Cephalopods are characterized by good memory, and they distinguish between short-term, intermediate and long-term memory. Octopuses and cuttlefish learn well, and they solve some problems as successfully as rats.

Among the sense organs, the eyes have reached the greatest complexity and perfection. The eyes are usually located in the recesses of the cartilaginous head capsule and have a cornea, an iris with a pupil capable of contracting and dilating, a lens and a retina. There is even an eyelid, as in onychotheutid squids, which can cover the eye.

The eye of an octopus is almost no different from the eye of mammals and humans. But there are still differences between them. For example, the cornea of ​​the eye in most cephalopods is not solid, but is pierced in front by a small (in cuttlefish) or rather wide (in squid) hole. The lens of the eye in cephalopods is not elliptical, but round, divided in half by a thin epithelial plate. Accommodation of the eye (setting vision to different distances, focusing) in cephalopods is achieved by moving it away or bringing it closer to the retina.

None of the inhabitants of the sea have such keen eyes as cephalopods. Only the eyes of an owl, a cat, and a human can compete with them.

And in terms of eye size, cephalopods hold the record. The cuttlefish's eye is only ten times smaller than itself. The giant squid has an eye the size of a car headlight. In many deep-sea cephalopods, the eyes occupy most of the head.

The suction cups of the hands contain tactile and taste buds. Cephalopods recognize the taste of food mainly with their hands. There are a huge number of taste-sensitive cells on the rims of the suckers, so each sucker is involved in tasting food.

Cephalopods also have olfactory organs: in squids these are papillae, or papillae, located on the head below the eyes, and in octopuses these are olfactory pits.

In the occipital part of the cartilaginous skull of cephalopods there are two statocysts - organs of balance. These are a pair of bubbles filled with liquid and containing calcareous pebbles inside - statoliths. At the slightest change in body position, the statoliths touch sensitive cells and the walls of the vesicle, and the animal orients itself in space.

As for hearing, it is not yet clear whether cephalopods have it. They are believed to be deaf, and it has even been suggested that deafness is a special adaptation that protects these mollusks from shock that can be caused by the sonar of whales - their worst enemies.

Cephalopods live only in oceans and fully saline seas. The salt content in water must be at least 33  0. therefore, these mollusks are not found either in the Black or Baltic Seas. They are extremely numerous in tropical and subtropical waters, but also live in temperate waters and polar seas.

Cephalopods have been consumed as food for a long time. In China, Japan and Korea, the use of these animals as food goes back centuries; in Mediterranean countries it also has a very long history. Ancient writers, in particular Aristotle, Plutarch and Pliny, report that in ancient Greece and ancient Rome, skillfully prepared octopus was a common food. Cephalopods were also used in medicine and perfumery. Jewelry was made from beautiful nautilus shells, and paint and ink were made from the ink liquid of sepia cuttlefish.

And until now, in the countries of the Mediterranean and Southeast Asia, cephalopods are very popular. They are prepared in ice cream, fresh, dried and canned form.

Recently, interest in cephalopods has increased sharply. It is caused by the unfavorable state of fish stocks and the need to find additional biological resources that are not yet used by fisheries, which could make up for the deficiency of protein foods. Therefore, a whole complex of features puts cephalopods in the category of valuable commercial animals. In terms of basic nutritional indicators - calorie content and protein composition - squid and other cephalopods are superior to other edible shellfish and even some fish and are only slightly inferior to beef and veal.

To this should also be added a high yield of production - 80% of the mass of the mollusk is used for food. Moreover, even the insides of cephalopods are valuable, since they contain a large number of different substances from which potent medicines can be prepared. Thus, cephalopods can be used completely, 100%.

Control questions:

What are the characteristic structural features of mollusks?

What classes is the phylum Mollusca divided into?

What are the main structural features characteristic of the class Gastropods?

What structure do bivalves have?

What structure do mollusks of the class Cephalopods have?

What is the significance of Mollusks in nature and human economic activity?

(Nautiloidea), represented by nautiluses ( Nautilus) And Allonautilus. In representatives of the subclass of bibranchs, the shell is reduced or completely absent, while in representatives of nautiloids the external shell remains. Cephalopods have the most advanced circulatory system and the most developed nervous system among invertebrates. Approximately 800 modern species have been described (fossil species number about 10 thousand), in Russia - 70 species. The most famous of the extinct groups: Ammonoidea (ammonites) and Belemnitida (belemnites), and of the modern ones: squids, cuttlefish and octopuses.

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Spreading

Cephalopods are common in all oceans at all depths, but most of them prefer to live in the benthic layer or on the bottom. They live only in fully saline water bodies. However, there is an exception - squid Lolliguncula brevis, found in the Chesapeake Bay, can withstand hard water with relatively low salinity - up to 17 ppm.

Dimensions

The body length of cephalopods ranges from a few centimeters to 18 meters (with elongated tentacles) in some squids.

Unlike many other cephalopods, nautiluses have poorly developed vision. Their eyes, otherwise well-shaped, do not have a crystalline lens (lens) and are an open chamber with an opening through which light enters the retina through a layer of water. The lack of vision in nautiluses is compensated by a good sense of smell, which allows the nautilus to find prey and mating partners.

Excretory system

The excretory system consists of 4 or 2 kidneys. Their external openings lie on the sides of the powder, on special papillae, the internal ends of the kidneys open, as always, into the pericardial part of the coelom. The kidneys are large sacs, sometimes merging with each other along the midline of the body.

Passing in close proximity to the kidneys, the afferent gill vessels (with venous blood) form numerous fringed blind protrusions (venous appendages), which protrude into the walls of the kidneys, this facilitates the extraction of metabolic products from the blood by the kidneys.

Change in color. Bioluminescence

Most cephalopods have controlled pigment cells called chromatophores, which allow them to change color and mimic the color of the surrounding background. The color of a mollusk can change in milliseconds. As a rule, coastal species have a brighter color palette. And those that prefer the open ocean are limited in camouflage. In addition to blending into the surrounding background, some cephalopods have the ability to bioluminesce. They can glow from the underside to camouflage their shadow from predators that may be lurking below. This property can also be used to lure prey (some molluscs put on colorful displays), attract the opposite sex, and even communicate with each other. The nature of the bioluminescence of these animals has not yet been fully elucidated. Presumably the light is produced by special symbiotic bacteria.

Ink bag

With the exception of Nautilidae and some species of octopuses belonging to the subclass Cirrina, all currently known cephalopods have an ink sac that may be used for defense against predators. This pouch is a muscular bursa that formed as an extension of the hindgut. It is located below the intestine and opens into the anus, through which the contents of the sac are expelled. The dark color of the ink is given by a pigment from the melanin group. The cloud of ink is usually mixed with mucus (produced by another part of the mantle) and water, forcefully pushed out during jet propulsion. This creates a smoke screen that disorients (and possibly leads to chemical irritation) the predator. Sometimes more complex behavior was observed. The mollusk released a cloud containing a large amount of mucus, which was approximately shaped like the mollusk itself. While the predator attacked the bait (referred to as a pseudomorph), the mollusk managed to swim away.

Circulatory system

Cephalopods are the only class of mollusks with a closed circulatory system. They have 2 hearts located in the gills (better known as “gill hearts”), which drive blood through the capillaries of the gills. The main heart then pumps oxygenated blood to all organs of the body.

Like most mollusks, cephalopods use hemocyanin (a protein containing copper) rather than hemoglobin to transport oxygen. Therefore, their blood is colorless and turns blue as a result of interaction with oxygen.

Respiratory system

Most cephalopods have one pair of comb-like gills, which are located in the mantle cavity. Nautiluses have two pairs of gills. Rhythmic contractions of the mantle serve to change water in the mantle cavity, and therefore ensure gas exchange. The larger the gills, the less the organism moves, since when moving slowly they are less likely to pass water through the mantle cavity, so a larger volume is needed to ensure their function.

Locomotion

Most cephalopods use a jet stream for movement, which they release from the mantle cavity through a funnel.

Nutrition

All cephalopods are predators, feeding on small fish, crabs, mollusks and other animals. They have various adaptations for hunting, capturing and killing prey. There are chitinous jaws resembling a beak for tearing prey, a crop, a complex stomach, intestines and anus that open into the mantle cavity. They are the only mollusks that have both a liver (digestive gland) and a pancreas. The liver opens into a blind spiral outgrowth of the stomach. Most cephalopods have sharp hooks in the suckers on their tentacles for grasping prey or venom.

Reproduction

Cephalopods are dioecious. Males are usually smaller than females, sometimes dwarf. One of the tentacles, the hectocotylus, is used for fertilization. With it, the male takes out packets of sperm - spermatophores - from the mantle cavity and transfers them to the mantle cavity of the female. The female lays fairly large eggs, often in a special structure made of stones and shells, and diligently guards the nest so that the young do not die after hatching. But the female Argonaut (octopus) from the secretions creates a shell as thin as parchment, in which she bears her offspring. She is half a meter tall, and the male is tiny (fits on a human thumbnail). Its genital tentacle - the hectocotylus - breaks off during fertilization and crawls through the funnel into the cavity of the female.

Origin

Some scientists consider the genus to be the very first cephalopod Nectocaris from the Cambrian period.

Cephalopods with external shells were especially common in the Cambrian, but most became extinct. Now only a few families of shelled cephalopods (nautiloids, Nautiloidea) remain, the best known of which are the nautili. In the Lower Carboniferous, the first representatives of higher cephalopods arose, in which the shell was gradually reduced and found itself enclosed inside the soft tissues of the body.

Classification

The class has 3 subclasses:

• † Subclass Ammonoidea - Ammonoids
• Subclass Nautiloidea - Nautiloids
• Subclass Coleoidea [ syn. Dibranchia] - Dibranchia

Remains of extinct representatives have been found for all of the above subclasses, as well as for the following groups (ranking higher than the genus):

• † Subclass Bactritoidea Shimanskiy, 1951 - Bactritoids
• † Subclass Endoceratoidea Teichert, 1933 - Endoceratoidea
• † Subclass Orthoceratoidea M"Coy, 1844 or Zhuravleva, 1994
• Subclass incertae sedis
  • †Order Actinocerida Teichert, 1933
  • †Order Ascocerida Kuhn, 1949
  • †Order Aulacocerida
  • †Order Barrandeocerida Flower & Kummel Jr., 1950
  • †Order Belemnitida Gray, 1849 - Belemnites
  • †Order Discosorida Flower, 1950
  • †Order Ellesmerocerida Flower & Kummel Jr., 1950
  • †Order Endocerida Teichert, 1933
  • †Order Oncocerida Flower & Kummel Jr., 1950
  • †Order Tarphycerida Flower & Kummel Jr., 1950
  • † ? Order Protactinocerida
  • †Order Pseudorthocerida Barskov, 1968
  • † ? Order Yanhecerida
  • Squad incertae sedis
    • †Superfamily Mesoteuthoidea Naef, 1921
    • Superfamily incertae sedis
      • †Family Anomalosaepiidae Yancey & Garvie, 2011
      • †Family Deltoceratidae Ulrich et al., 1942
      • †Family Spirulirostridae Naef, 1916
      • Family incertae sedis
        • † Subfamily Michelinoceratinae Flower, 1945

Previously, modern representatives of the class were divided into two subclasses: four-branchia (Tetrabranchia) and two-branchia (Dibranchia).

Cephalopods and humans

Among the enemies of cephalopods are fish, birds, mammals, including humans.

There are many legends and fictions about cephalopods (see kraken, octopuses in popular culture), but there are not so many reliable facts about their attacks on people.