Vertebrates are considered the highest subphylum of the Chordata phylum. While tunicates and non-cranial are lower chordates. There are more than 40 thousand species of vertebrates. They are diverse in structure, size, life activity, habitats. At the same time, they have a number of common features, especially during the period of embryonic development, which indicates the commonality of their evolutionary origin.
Almost all vertebrates have a highly developed nervous system and lead an active lifestyle (looking for food and breeding partners, running away from danger).
The first discovered remains of vertebrates belong to the Silurian.
Vertebrates include: cyclostomes, cartilaginous and bony fishes, amphibians, reptiles, birds and mammals (animals). Cyclostomes are jawless. The remaining classes of the subtype belong to the section Jaws.
Musculoskeletal system of vertebrates
Aromorphoses: the formation of an axial skeleton in the form of a spinal column; skull appearanceforbrain protection; development of jaws for grasping prey and, in more highly organized ones, grinding food; the appearance of paired limbs,allowingmove quicklyto bein space.
The skeleton of vertebrates is cartilaginous or bone (in most). Its main functions are to ensure the movement of the animal and protect its internal organs. In addition, the bones of the skeleton serve as a place of attachment of the muscles of the body, blood formation occurs in individual bones, and a number of substances are stored.
The spine is formed on the basis of the notochord. In a number of vertebrate species (lampreys), the notochord is preserved in the adult state, but cartilage protecting the spinal cord develops around it. In sturgeons, the upper and lower vertebral arches form around the notochord.
In most vertebrates, the spine consists of separate, relatively mobile vertebrae relative to each other. Each vertebra has a body, upper and lower arches. The spinal cord passes through the canal of the superior arch. The arches of the vertebrae serve as protection for the spinal cord. Ribs are attached to the vertebrae to protect the organs of the chest cavity.
The vertebrate skeleton is divided into:
Axial skeleton- spine and brain skull.
Visceral skeleton- gill arches and bones derived from gill arches (jaws and some others).
Skeleton of limbs and their girdles(excluding lampreys and hagfish).
Limbs are of two main types - fin and five-fingered limb. In the fin, the cartilages or bones of the limb move relative to their girdle as a single lever. The five-fingered limb of terrestrial animals is a series of levers that move independently relative to each other and the limb belt.
The muscles of the body are formed striated muscles. In higher vertebrates (reptiles, birds, mammals), the muscles are divided into separate bundles. In lower vertebrates, the muscles are segmented.
There are smooth muscles of internal organs. It is called visceral.
Nervous system and sensory organs of vertebrates
Aromorphoses: the formation of the brain, dividing it into five departments,performing different functions (anterior, intermediate, middle, medulla oblongata and cerebellum).
The neural tube in vertebrates differentiates into the spinal cord and brain, which together form the central nervous system. In addition to it, the peripheral, sympathetic, parasympathetic and autonomic nervous systems are distinguished.
A developed brain provides complex behavior, including collective behavior. Higher nervous activity is the basis of adaptive behavior.
The neurocoel (a cavity inside the neural tube) in the brain turns into the ventricles of the brain. 10-12 pairs of nerves depart from the brain (olfactory, visual, oculomotor, trochlear, trigeminal, abducens, facial, auditory, glossopharyngeal, vagus, accessory, sublingual). The nerves leave the spinal cord in pairs.
The sense organs provide the connection of the body with the external environment. In vertebrates, they are diverse and have a complex structure. Eyes with a lens, the shape of which can change in terrestrial vertebrates. In fish, the lens can move to achieve clarity of the image.
The organs of hearing are connected with the organs of balance. Different groups of vertebrates have different structures. The olfactory cavity opens outward through the nostrils. The skin contains receptors for touch, temperature, pressure, etc.
The circulatory and cardiovascular system of vertebrates
Aromorphoses: appearance of the heartprovidingfast blood flow;complete separation of arterial and venous blood flow in birds and mammals, as a result of which the appearance of warm-bloodedness, which allowed animals to be less dependent on adverse conditions of the abiotic environment.
Vertebrates, like all chordates, are characterized by a closed circulatory system.
The number of heart chambers (from 2 to 4) depends on the level of organization of the class. The lower vertebrates have one circle of blood circulation. In this case, venous blood passes through the heart, which then goes to the gills, where it is saturated with oxygen, then arterial blood is carried throughout the body. The pulmonary (second) circulation first appears in amphibians (amphibians).
The blood of vertebrates consists of plasma, which contains red and white blood cells.
Vertebrate skin
Aromorphosis: appearance ddouble layerohleatherand.
The superficial layer of the skin stratified epidermis. It develops various glands (sweat, sebaceous, mucous, etc.) and a number of solid formations (claws, hair, feathers, scales). Inner layer of skin dermis which is a strong connective tissue. Here, such solid formations as bone scales, skin (overhead) bones are also formed.
Digestive system of vertebrates
In the digestive system of vertebrates, five sections are distinguished: the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine. In the course of evolution, the intestine gradually lengthened.
Digestive glands: salivary, liver, pancreas.
Respiratory system of vertebrates
Gills in cyclostomes, fish and amphibian larvae. Lungs - in all other vertebrates. In lower vertebrates, skin respiration plays an important role.
Gills are lamellar outgrowths of the walls of the gill slits. In such plates there is a network of small blood vessels.
In the process of embryonic development, the lungs are formed as a pair of outgrowths of the pharynx. Amphibians and reptiles have sac-like lungs. Birds have a spongy structure. In mammals, the branches of the bronchi terminate in alveoli (small vesicles).
excretory system of vertebrates
The excretory organs of vertebrates are a pair of kidneys. The kidneys have a different structure in different groups of vertebrates. There are head, trunk, pelvic kidneys. In the process of embryogenesis, there is a change of head to trunk or trunk to pelvic.
Reproductive system and embryonic development of vertebrates
Almost all vertebrate species are dioecious. There are paired sex glands (testes or ovaries). With the exception of cyclostomes, the rest have special ducts that remove reproductive products.
Jaws are divided into two groups: anamnia and amniotes. Anamnias include fish and amphibians, since their larval stage lives in water, and the development of the embryo takes place without the formation of special embryonic membranes. For anamnia, external fertilization is usually.
Amniotes include reptiles, birds and animals. Their embryo has embryonic membranes (amnion and allantois). Characterized by internal fertilization.
Vertebrate organ systems
| Parameter name | Meaning |
| Article subject: | Vertebrate organ systems |
| Rubric (thematic category) | Ecology |
| Organ system | System functions | Organs that are part of the system |
| body integuments | The integuments of the body separate the body of the animal from the external environment and protect it from the action of adverse factors. At the same time, they do not allow the animal's body to give the substances it needs to the external environment. In many animals, the integument of the body plays an important role in the processes of gas exchange. | Leather |
| Musculoskeletal | The musculoskeletal system of the animal ensures its movement in space. It is also the frame of the animal's body and helps it maintain a certain shape. Another function of the musculoskeletal system is protective - it protects internal organs from mechanical damage. | Skeleton and muscles |
| digestive | The digestive system provides the body with nutrients. It processes organic substances that enter the body from the external environment. | Teeth, tongue, salivary glands, esophagus, stomach, intestines, liver, pancreas |
| Transport | The transport system ensures the rapid transfer of substances from one part of the body to another. It also plays an important role in the regulation of many processes, as it is a carrier of hormones, nutrients and metabolic products. | Heart, arteries, veins, capillaries |
| Respiratory | The respiratory system delivers oxygen to the body and removes carbon dioxide from it. | Lungs, gills, skin |
| excretory | The excretory system removes metabolic products from the animal's body. | Kidneys, lungs, skin, ureter, bladder |
| endocrine | The endocrine system is involved in the regulation of the work of individual organs and organ systems of the body. It provides long-term reactions of the body to changing conditions. Biologically active substances - hormones - are used to transmit signals in the endocrine system. | Hypothalamus, pituitary, pancreas, gonads, thyroid, pineal gland |
| nervous | The nervous system deciphers the indications of the sense organs and coordinates with them the actions of all other organs. It is also involved in the regulation of the work of individual organs and organ systems of the body. The nervous system provides quick reactions of the body to changing conditions | Brain, spinal cord, nerves |
| sense organs | The sense organs of animals perceive information from the environment and transmit it to the nervous system. | Organs of touch, smell, taste, hearing, sight, balance |
| reproductive | The reproductive system ensures the reproduction of animals | sexual organs |
3. Regulation of functions in multicellular organisms.
The regulation of the functions of the organism of animals is best considered on the example of a person. There are two basic methods of regulation: nervous (using nerve impulses that are transmitted through the membranes of nerve cells) and humoral (using chemicals that are carried by different body fluids).
Humoral regulation- coordination of the physiological functions of the body with the help of chemicals that are carried by different body fluids (blood, lymph, tissue fluid), - hormones. Done by the endocrine system.
Endocrine system- a set of organs, parts of organs, and individual cells that secrete hormones into the blood and lymph. Together with the nervous system, it regulates and coordinates important functions of the human body: growth, reproduction, metabolism, adaptation processes.
In the endocrine system, the central and peripheral sections are distinguished, which interact with each other and form a single system. The basis for the effective functioning of the endocrine system is the use of the feedback principle.
Nervous regulation of processes in the human body is carried out with the help of somatic and autonomic nervous systems.
The somatic nervous system consists of those parts of the central and peripheral nervous systems that innervate the skeletal muscles and sensory organs. It provides the body with the perception of information from the external environment, as well as actions (in the form of various movements of skeletal muscles) in response to external factors.
The movements that are provided by the somatic nervous system are implemented using the coordinated actions of individual motor units (groups of muscle fibers, each of which is innervated by one motor neuron).
Autonomic (vegetative) nervous system- part of the nervous system that regulates the activity of internal organs, glands, blood vessels, smooth and some striated muscles, and also manages metabolic processes.
The autonomic nervous system consists of two parts that have an opposite effect on the organs and tissues of the body - the sympathetic and parasympathetic divisions. The highest control center of the autonomic nervous system is the hypothalamus, which also controls the activity of the endocrine system.
The autonomic nervous system provides innervation to internal organs, the vascular system, glands, and smooth muscles. It also has a trophic effect on skeletal muscles. Without causing contraction of these muscles, it improves their nutrition and thus stimulates their work. It regulates the activity of internal organs and blood vessels, the secretion of glands, and the work of the heart. Metabolic processes are also regulated by the autonomic nervous system.
The activity of the autonomic nervous system is not subject to the will and consciousness of man. A person does not even feel the presence of many internal organs, especially those that do not move, like, for example, glands, does not feel how they secrete, how food is absorbed in the intestines, and the like. A person cannot consciously control the activity of these organs, as he controls his muscles. Such processes take place outside the consciousness of a person and not subject to her will.
In the autonomic nervous system, as in the somatic, there are central and peripheral parts. The central part is represented by vegetative neurons, which form an accumulation in the brain and spinal cord - vegetative nuclei. The peripheral part is formed by numerous autonomic nerve nodes and nerve fibers.
Vertebrate organ systems - concept and types. Classification and features of the category "Organ systems of vertebrates" 2017, 2018.
To establish the phylogeny, data from comparative anatomy and embryology were used (Kovalevsky, Severtsev). Their work suggests that the ancestors of chordates were limitedly mobile, crawling, near-bottom, bilaterally symmetrical, with a notochord along the entire length of the body, an undivided neural tube, and muscle segments. The number of segments is small, as are the gill slits (passive feeding). Further evolution proceeded in three ways: 1) individuals of one branch, primarily without a skull, increased their mobility and acquired active nutrition, switched to a nekton (swimming) way of life and gave rise to the first primitive vertebrates; 2) another branch retained the bottom way of life, but developed devices for digging into the ground and simplified the original organization. Another characteristic feature of the change in the structure of the body: part adapted to lying on its side => the anus and mouth have shifted to the left (lower) side, and the gill slits to the right (upper). A reflection of this phylogenetic stage may be the asymmetry of the lancelet. The development of the myochordal complex increased mobility, and the growth of the pharynx, the increase in the number of gill slits, and the development of the atrial cavity made it possible to switch to life in the ground, while maintaining passive nutrition. This branch has survived to the present day in the form of skullless ones that have mastered simple biocenoses in the form of sandy soils (without competition and the danger of enemies). A small number of non-cranial, limited development of the seas by them reflects the inconsistency of their organization: passive feeding against high mobility; 3) primitive non-cranial at an early stage of evolution switched to a benthic sedentary lifestyle on hard ground. Powerful tunics formed on the surface of the body protected the sea squirts from many enemies. The development of the filtering apparatus ensured the receipt of food during an immobile lifestyle and with passive nutrition. These features were developed through regressive evolution, during which the structure of adult animals was simplified: the notochord, neural tube and sensory organs were reduced. The presence of a complex and mobile larva allowed the ascidia to settle, and asexual reproduction (budding) made it possible to quickly settle => a strong position in the seas.
ORGANIZATION OF VERTEBRATE ANIMALS
Vertebrates are united by a common morphophysiological organization. In all organ systems of these animals, one can trace the features of successive changes in connection with the evolutionary transformation of homologous organs. Below is a general plan of the structure, functioning and laying in the ontogeny of individual organ systems.
Skin represent a very important functional system. The skin is in direct contact with the external environment and is directly affected by it. The skin and muscles form the body of the animal from the surface, give it shape and hold all the internal organs. The skin covers protect the body from external mechanical and chemical damage, exposure to temperature, desiccation, penetration of microbes. The skin takes part in thermoregulation, gas exchange and excretion of decay products. Derivatives of the skin can take part in the formation of organs of locomotion (hooves), serve for grasping (claws), attack and defense (horns, needles, etc.), flight (folds), swimming (webs).
The skin contains receptors of the organs of touch, it has many glands for various purposes (mucous, fatty, odorous, sweat, etc.).
Vertebrate skin is characterized by two layers. The outer layer - the epidermis - is of ectodermal origin. It is always multilayered. Its lower layer remains alive and active for life and produces new layers of cells. The upper layers of the epidermis are usually composed of flattened cells, which in terrestrial vertebrates become keratinized, die off and constantly
slough off. The epidermis gives rise to horny derivatives of the skin - horny scales, feathers, hairline, claws, hooves, hollow horns. Various skin glands develop in the epidermis.
The inner fibrous layer of the skin corium, otherwise referred to as cutis, or the skin itself, develops from the mesodermal rudiment - the skin leaf of the somite. The layer of corium is thick, it makes up the main part of the skin, which has great strength. In the corium, various ossifications develop in the form of fish scales, integumentary bones, forming the so-called skin skeleton (in contrast to the chondral skeleton). At the expense of the skin itself, bone antlers of deer also develop. In the lower part of the cutis, a subcutaneous layer of fat accumulates.
musculature. The layer of muscles located under the skin is the bulk of the musculature, called body musculature, or somatic. It provides animals with the ability to move in the environment and consists of striated muscle tissue. In lower vertebrates, as in non-cranial ones, the musculature has a segmented character. In higher vertebrates, due to the general complication of body movements, with the development of limbs, segmentation is disturbed, and the trunk muscles are grouped, forming such parts of the body as the torso, head, and organs of movement.
Except somatic muscles Vertebrates have the muscles of the intestines and some other internal organs (vessels, canals). This muscle is called visceral. It is composed of smooth muscle tissue and provides, in particular, the movement of food in the intestines, the contraction of the walls of blood vessels.
Trunk musculature embryonicly arises from the inner layer of the myotome (see the development of the lancelet), i.e. dorsal mesoderm. The visceral musculature is a derivative of the lateral plate, i.e. abdominal mesoderm.
Internal skeleton- This is the supporting base of the body of a vertebrate animal. In addition, the skeleton is involved in the movement of the body, protects the internal organs.
Topographically, the skeleton of vertebrates can be divided into axial, visceral, limb girdle and free limb skeletons.
The axial skeleton in its original form is presented chord surrounded by a thick connective tissue membrane. The latter covers not only the chord, but also the neural tube lying above it. The notochord develops from the rudiment of the dorsal side of the primary intestine, i.e. is of endodermal origin.
Rice. 9. Formation of a vertebra (transverse sections):
1 - the beginning of the lower arc; 2 - the beginning of the upper arc; 3 - rib, 4 - hemal process, 5 - lateral process of the vertebra, 6 - superior arch
In most vertebrates, the notochord is displaced and replaced by a cartilaginous or bony skeleton. The cartilaginous and bone skeletons develop as derivatives of the above-mentioned connective tissue (mesoderm in origin) membrane. This shell is thus skeletal.
In the axial skeleton there are vertebral column and cerebral skull. During the development of the vertebrae, metamerically located paired cartilages adjacent to the surface of the notochord are initially laid. These are the rudiments of the upper and lower vertebral arches (Fig. 9.1). The growth and closure of the outer ends of the upper arches leads to the formation spinal canal, in which the neural tube is located (Fig. 9, II). The lower arcs close in the caudal region (in fish) and limit hemal canal, where do the dorsal aorta and tail vein pass. As a result of the closure of the inner ends of the upper and lower arches, the vertebral bodies are formed, inside and between them, to some extent, a notochord can be preserved (Fig. 9, III). In the trunk region, ribs are attached to the processes of the lower vertebral arches.
brain skull, or cranium, is laid in the form of two pairs of cartilage lying under the rudiment of the brain. Their back pair - parachordalia- located on the sides of the front end of the chord; front pair - trabeculae- in front of her. They transform the rudiments of the first vertebrae and partly the arches of the visceral skeleton. The growth and closure of the parachordalia and trabeculae lead to the formation of the main lamina of the skull, which underlies the brain. At the same time, cartilaginous capsules appear around the sensory organs (smell, sight, hearing) that are being formed. They are located slightly above the level of the main
Rice. 10. Shark Cartilaginous Skull Development:
1 - gill arches; 2 - hyoid arch; 3 - jaw arch; 4 - auditory capsule; 5 - chord; 6 - pituitary gland; 7 - gut; 8 - midbrain; 9 - spinal cord; 10 - nostril; 11 - eye; 12 - parachordalia; 13 - primary forebrain; 14-orbital cartilages; 15 - trabeculae
plates of the skull and cover the brain from the sides. In subsequent development, the capsules of the sense organs are connected and fused with the main lamina of the skull. In the cartilaginous state of the skull, a full roof does not occur at the braincase. The holes remaining between the lintels of the skull roof - fontanelles- Tightened by a connective tissue membrane. A solid roof of the skull occurs only in connection with the formation of superimposed (skin) bones (frontal, parietal).
Thus, the brain skull arises in connection with the development of the brain and sensory organs as their protective formation.
Visceral skeleton phylogenetically formed independently of the cranium (Fig. 10). Its laying occurs in the connective tissue near the front of the digestive tube. Initially, the visceral skeleton is a series of numerous monotonous arches located between the gill slits. They serve as a support for the respiratory apparatus.
The subsequent transformation of the visceral skeleton is associated with the acquisition by vertebrates of such organs as the upper and lower primary jaws, the middle ear, the floor of the brain skull, and the larynx.
The concept of "visceral skeleton" is considered mainly in relation to lower vertebrates. In higher education it is replaced by the concepts of "visceral skull", "facial skull".
Skeleton of limb girdle and free limbs. In vertebrates, unpaired and paired limbs are distinguished. In turn, paired limbs can be either fins or ground-type limbs.
Skeleton of unpaired limbs - dorsal, caudal, anal fins- consists of a number of cartilaginous or bone rays that are not associated with other parts of the skeleton.
The skeleton of paired limbs is subdivided into the skeleton of the limb belts and the skeleton of the free limb. Limb belts are always located inside the body of the animal. The free limb skeleton in vertebrates is of two types: fish fin and
Rice. 11. Scheme of vertebrate skeletons:
I - fish skeleton, II - terrestrial vertebrate skeleton
five-fingered limb terrestrial vertebrates. In the first case, the skeleton is represented by several rows of cartilage or bones that move relative to the belt as a single lever. The skeleton of a five-fingered limb consists of a number of levers that can move both together relative to the limb belt, and separately - one relative to the other (Fig. 11). The laying of the limb skeleton occurs in the connective tissue layer of the skin.
Digestive organs. The digestive system is represented by a tube that begins with the mouth and ends with the anus. The digestive tract is formed from the endodermal tube of the gastrula (see development of the lancelet). In this regard, the epithelium of the digestive tract is endodermal. Only in the region of the oral and anal openings does the endodermal epithelium imperceptibly pass into the ectodermal. This is due to the invagination of the body walls (and, consequently, the ectoderm) during the formation of the above holes.
The digestive tract is divided into the following main sections: 1) oral cavity serving for eating; 2) pharynx- a department always associated with the respiratory organs: in fish, gill slits open into the pharynx, in terrestrial vertebrates, a laryngeal slit is located in the pharynx; the pharynx is rightly called the respiratory section of the digestive tube; 3) esophagus, 4) stomach- expansion of the intestinal tract, which in some cases has a very complex device; 5) intestines, typically subdivided into the anterior, or thin, middle, or thick, and hind, or rectum. Morphological complication of the intestinal tract in a series of vertebrates follows the path
its elongation and differentiation into departments. The ducts of three types of digestive glands open into the digestive tube: salivary, liver, pancreas.
Salivary glands- Acquisition of terrestrial vertebrates. They transform the mucous glands of the oral cavity. Their secret moistens food and promotes the breakdown of carbohydrates.
The liver and pancreas develop by protrusion of the anterior part of the embryonic gut. The liver arises from a blind outgrowth of the abdominal wall of the intestine (see hepatic outgrowth of the intestine of the lancelet). The liver ducts drain into the anterior small intestine. Pancreas develops from several, more often from three, rudiments, which are also outgrowths of the intestine. This gland, unlike the liver, usually does not have the appearance of a compact body, and its lobules are scattered throughout the mesentery of the anterior small intestine.
The functions of both of these glands are wider than just digestive ones. So, the liver, in addition to secreting bile, emulsifying fats and activating the action of other digestive enzymes, is an important metabolic organ. Here, some harmful decay products are neutralized, glycogen accumulates. Pancreatic enzymes break down proteins, fats and carbohydrates. At the same time, the pancreas serves as an organ of internal secretion. A breakdown in this function leads to a loss of the body's ability to use sugar. The result is a severe disease - diabetes.
Respiratory system There are two types of vertebrates - gills and lungs, and in a significant part of vertebrates, the skin is essential in respiration.
The gill apparatus is a system of paired, usually symmetrically located, slits that serve to communicate the pharynx with the external environment. The anterior and posterior walls of the gill slits are lined with a mucous membrane that forms lamellar outgrowths; outgrowths are divided into petals, bearing the name gill. Each gill plate above the petals is named half-gills. In the intervals between the gill slits (in the gill septa) decompose visceral gill arches(See p. 27 for the visceral skeleton). Thus, each gill arch is connected to two half-gills of two different gill slits.
Gill slits are laid in the form of a system of paired endodermal protrusions growing outward from the pharynx. At the same time, ectodermal invaginations of the outer integument appear. The primordia grow towards each other and then unite. Therefore, gill slits are of mixed ento- and ecto-dermal origin. Gill filaments Usually
develop from the ectodermal rudiment of the fissure, and only in jawless animals do they have an endodermal origin.
Respiratory organs of terrestrial vertebrates - lungs- in the scheme they are a pair of bags that open into the pharynx through the laryngeal fissure. Embryonally, the lungs arise in the form of a protrusion of the abdominal wall of the pharynx in the back of the gill apparatus, i.e. are of endodermal origin. In the early stages of embryonic development, the lung buds resemble a pair of internal (endodermal) gill slits. These circumstances, as well as the blood supply and innervation features common to the lungs and gills, force us to consider the lungs as homologues of the posterior pair of gill sacs.
Leather participates in respiration in cases where there are no dense horny or bony scales in it, for example, in amphibians, naked-skinned fish.
Functionally, the respiratory system is involved in the enrichment of blood with oxygen and in the removal of carbon dioxide. Ammonia is released through the respiratory system in lower aquatic animals. In warm-blooded animals, it is involved in the processes of thermoregulation. The principle of operation of the respiratory system is the exchange of CO 2 and O 2 between gas and blood flows, directed countercurrent towards each other.
Rice. 12. Circulatory scheme of fish (I) and terrestrial vertebrate (II):
1 - branchial arteries; 2 - carotid artery; 3 - dorsal aorta; 4 - abdominal aorta; 5 - pulmonary artery; 6 - Cuvier duct; 7 - anterior cardinal (jugular) vein; 8 - posterior cardinal vein; 9 - posterior vena cava; 10 - hepatic vein; 11 - pulmonary vein; 12 - portal vein of the liver; 13 - subintestinal vein
Circulatory organs. The circulatory system in vertebrates, like in non-cranial ones, is closed. The circulatory system is laid from the inner sheets of the lateral plates (see the development of the lancelet). It consists of interconnected blood vessels, which in a rough scheme can be reduced to two trunks: dorsal where blood flows from head to tail, and abdominal along which it moves in the opposite direction. Unlike non-cranial (Fig. 12), in vertebrates, the movement of blood is associated with the activity of the heart.
The heart is a thick-walled muscular bag, divided into several sections - chambers. The main parts of the heart are the atrium, which receives blood, and the ventricle, which directs it through the body. The number of heart chambers is different in different classes of vertebrates.
Embryonally, the heart arises as an expansion of the posterior part of the abdominal aorta, which in this place coils into a curved loop. The anterior part of the loop gives rise ventricle hearts, back - atrium.
The heart has striated muscles that work in automatic mode, and its contraction is not subject to volitional impulses. The dimensions of the heart are related to the intensity of its work, and its dimensions relative to the dimensions of the body increase in the series of vertebrates (Table 1).
Table 1
Cardiac index in vertebrates of different classes
The blood vessels are divided into two systems: arterial in which blood flows from the heart, and venous through which blood returns to the heart. In the process of complication of vertebrates, there is a transition from animals having one circle of blood circulation to owners of two circles of blood circulation.
By its nature, blood refers to connective tissue penetrating into the bloodstream from the intercellular space.
The blood of vertebrates consists of a colorless liquid - plasma, in which the formed elements of blood are located: red blood cells, or erythrocytes, containing a dye - hemoglobin, and white blood cells - leukocytes. Red blood cells are associated with blood oxidation, as they carry oxygen. Leukocytes are involved in the destruction of microorganisms that have entered the body. In addition, there are platelets in the blood, which play an important role in blood clotting, as well as other cells. The mass of blood in the evolutionary series of vertebrates increases (Table 2).
table 2
Relative mass of blood to body mass in vertebrates of different classes
(after Prosser and Brown, 1967; after Prosser, 1978)
The circulatory system is multifunctional. It is involved in the receipt by organs, tissues, cells of oxygen, organic and mineral substances, liquids and the removal of decay products, toxins, carbon dioxide, in the transfer of hormones of the endocrine glands, etc.
Along with the circulatory system, vertebrates have another vascular system associated with it - lymphatic. It consists of lymphatic vessels and lymph glands. The lymphatic system is not closed. Only its large vessels have independent walls, while their branches open into the intercellular spaces of various organs. Lymphatic vessels contain a colorless fluid - lymph, in which lymphocytes, formed in the lymph glands, float. The movement of lymph is determined by the contraction of the walls, some sections of large vessels (the so-called lymphatic hearts) and periodically changing pressure on the vessels of various organs.
The lymphatic system serves as an intermediary in the exchange of substances between the blood and tissues.
Nervous system. The functions of the nervous system are the perception of external stimuli and the transmission of emerging excitations to cells, organs, tissues, as well as the unification and coordination of the activities of individual organ systems and the body as a whole into a single functioning living system. Embryonally, the nervous system of vertebrates arises, just as in non-cranial ones, in the form of a hollow tube laid in the ectoderm on the dorsal side of the embryo (Fig. 13). Subsequently, its differentiation occurs, leading to the formation of: a) central nervous system, represented by the brain and spinal cord, b) peripheral nervous system, consisting of nerves extending from the brain and spinal cord, and c) sympathetic nervous system, consisting in the basis of nerve nodes located near the spinal column and connected by longitudinal strands.
The brain is represented in vertebrates by five sections: anterior, intermediate, middle, cerebellum and oblong brain. It is laid embryonic in the form of swelling of the anterior part of the neural tube, which soon divides into three primary cerebral vesicles (Fig. 14). In the future, the first cerebral bladder gives rise to the front of the forebrain; its back part is transformed into the diencephalon. The midbrain is formed from the second cerebral bladder. By protrusion
Rice. 13. Successive stages of development of the central nervous system of vertebrates (schematic cross sections):
I-II differentiation of the ectoderm; III invagination of the neural plate, IV-V - isolation of the neural tube, 1 epidermis; 2 ganglion plate
Rice. 14. Development of parts of the brain (scheme):
I - stage of three bubbles (with eye bubbles), II - stage of five departments (with eye cups), 1 - forebrain, 2 - diencephalon; 3 - midbrain; 4 - cerebellum; 5 - medulla oblongata; 6 - eye cup; 7 - eye bubble
the roof of the third cerebral bladder forms the cerebellum, under which the medulla oblongata is located. The forebrain is further divided into left and right halves.
Simultaneously with the growth and differentiation of the head section of the neural tube, a corresponding transformation of the neurocoel occurs. Its two extensions in the forebrain hemispheres are known as lateral ventricles brain. The expanded part of the neurocoel in the intermediate part of the brain is designated as third ventricle, midbrain cavity - as sylvian aqueduct, the cavity of the medulla oblongata - as fourth ventricle, or rhomboid fossa(Fig. 14). 10 or 12 pairs leave the brain cranial nerves.
The forebrain has two symmetrically located protrusions in front, from which the first pair of head nerves departs - olfactory(I). From the bottom of the diencephalon depart visual nerves (second pair of head nerves, II).
On the roof of the diencephalon, two protrusions sitting on legs develop: anterior - parietal organ and back - epiphysis.
An unpaired protrusion grows from the bottom of the diencephalon - funnel, which is adjacent to a formation that is complex in structure and function - pituitary. The anterior pituitary gland develops from the epithelium of the oral cavity, the posterior - from the medulla. It is located there hypothalamus.
The roof of the midbrain forms paired swellings - visual lobes (tubercles). The third pair of brain nerves depart from the midbrain ( oculomotor, III). Fourth pair of head nerves ( block, IV) departs at the border between the middle and medulla oblongata, all other head nerves (V - X - XII) depart from the medulla oblongata.
Spinal cord not delimited sharply from the medulla oblongata. In the center of the spinal cord (along the main axis of the organ), a neurocoel is preserved, known in vertebrates under the name spinal canal.
The spinal nerves depart from the spinal cord metamerically (according to the number of segments). They begin with two roots: dorsal - sensory and abdominal - motor. These roots fuse shortly after exiting the spinal cord to form the spinal nerves, which then divide again into the dorsal and abdominal branches.
sense organs. This group of organs arises as derivatives of different parts of the embryo and at different stages of its development. These are the organs of smell, vision, hearing, the vestibular apparatus, the organs of the lateral line, the organs of taste, touch, specific organs that perceive the Earth's magnetic field, electric fields, thermal radiation, etc.
Olfactory organs. It is believed that the sense of smell is one of the most ancient functions of the brain. The organs of smell are laid as a thickening of the ectoderm simultaneously with the neural plate. In parallel, the skeleton of the olfactory capsules, which are part of the brain skull, is formed. At first, the olfactory capsules communicate only with the external environment and have external nostrils. Subsequently, due to the terrestrial existence, the nostrils become through.
organs of vision also belong to the ancient sensory organs. Light-sensitive reception occurs at a very early stage in the evolution of chordates (remember the lancelet) and is formed in early embryogenesis. The organs of vision of vertebrates are divided into paired and unpaired. Both are outgrowths of the diencephalon. Paired eyes are laid as outgrowths of the lateral parts of the diencephalon, unpaired - as sequentially located in the roof of the diencephalon (pineal gland and parietal organ). The laying of paired eyes is accompanied by the formation of visual capsules around them, which are part of the brain skull (Fig. 15, 16).
hearing organs have a complex origin in vertebrates. The earliest in evolution is the inner ear, which
Rice. 15. Successive stages of eye development:
1 - diencephalon; 2 - the epidermis that forms the lens; 3 - the beginning of the formation of the eye cup; 4 - leg of the eye cup; 5 - lens; 6 - cornea; 7 - retina; 8 - pigment shell; 9 - mesoderm cells that form the choroid and sclera
Rice. 16. Sagittal section of the human eye:
1 - cornea; 2 - iris; 3 - anterior chamber; 4 - one of the muscles that move the eye; 5 - vitreous body; 6 - optic nerve; 7 - sclera; 8 - choroid; 9 - retina; 10 - ciliary muscle; 11 - ciliary body
is laid in the ectoderm of the embryo, deepens in the form of a hole and takes shape as auditory vesicle lying in the auditory capsule. The auditory vesicle is divided by constriction into two parts. The upper section turns into the vestibular apparatus. It is the organ of balance. It allows you to feel the position of the body in the three-dimensional space of the Earth. This body is 3 semicircular canal in the inner ear (Fig. 17, 18). The lower part of the auditory vesicle is the inner ear itself - auditory sac.
The middle and outer ear are formed in the late stages of the emergence of vertebrates in connection with landfall.
Lateral line organs characteristic only of primary aquatic vertebrates, are also laid in the ectoderm. They are grooves that stretch
Rice. 17. Successive stages of development of the inner ear:
I - auditory placode, II - fossa, III and IV - vesicle in section; V and VI - the formation of semicircular canals; 1 - rudiment of a snail; 2 - semicircular canal; 3 - endolymphatic duct; 4 - round bag; 5 - oval pouch
along the sides of the head and along the body. These grooves may or may not be covered by bony scales. The lateral line organs perceive light movements and water vibrations near the sources of vibrations: the speed and direction of currents, movements of one's own body and the presence of objects in the path of the animal in the water. They are a seismic sensor system.
organs of taste are laid in the endoderm and perceive the taste of food consumed in the range: sweet, bitter, sour, salty. They are located on the taste buds within the oral cavity.
sense organs. They do not have sensory cells, but are nerve endings branched in the skin, which perceive environmental objects by touch.
Rice. 18. Scheme of the membranous auditory labyrinth:
1, 2, 3 - anterior, external and posterior semicircular canals, 4 - endolymphatic duct, 5 - auditory spots, 6 - round sac, 7 oval sac, 8 - otoliths
Rice. 19. Bowman's capsule with vascular tangle:
1 - afferent blood vessel, 2 - efferent blood vessel, 3 - Bowman's capsule, 4 - vascular tangle, 5 - primary urine, 6 - renal tubule, 7 - funnel of the renal tubule (nephrostome) that opens into the body cavity
Rice. 20. Scheme of the urinary system of vertebrates:
I (male) and II (female) - sharks and amphibians, III (male) and IV (female) - reptiles and birds, V (male) and VI (female) - mammals, 1 - pronephros (pronephros); 2 - testis ; 3 - vas deferens, 4 - mesonephros (primary kidney), 5 - hindgut, 6 - bladder, 7 - cloaca, 8 - funnel, 9 - ovary, 10 - Muller canal, 11 - epididymis (remainder of the anterior part of the meso- nephros), 12 - vas deferens, 13 - metanephros (secondary kidney), 14 secondary ureter, 15 mesonephros rudiment, 16 oviduct, 17 ovum, 18 protein secreted by the glands of the oviduct wall, 19 - uterus, 20 - embryo in uterus 21 - vagina, 22 - genital sinus, 23 - prostate glands; 24 - seminal vesicle, 25 - vas deferens, 26 - epididymis, 27 - perineum; 28 - rudiment of the Muller canal, 29 - canal of the mesonephros (primary kidney); 30 - copulatory organ (penis), 31 - anus
excretory organs. All vertebrates have excretory organs kidneys designed to remove excess water, mineral salts and decomposition products of nitrogen metabolism in the form of urea or uric acid from the body. They are of mesodermal origin, laying on the outer wall of the somites. However, the structure and mechanism of functioning of the kidneys in different groups of vertebrates are not the same. In the process of evolution of vertebrates, three types of kidneys change: head, or pronephros (pronephros), trunk, or primary, kidney (mesonephros) and pelvic, or secondary, kidney (metanephros). Different types of kidneys have different principles of the excretion process: excretion from the body cavity, mixed excretion (from the body cavity and from the blood), and finally, only from the blood. At the same time, changes occur in the mechanism of water reabsorption. The release of water and the products of protein metabolism dissolved in it from the body cavity is possible due to the many funnel-shaped nephrostomas opening into the body cavity. Excretion from the blood occurs through the Malpighian bodies of the kidneys. The excretory ducts from the kidneys are called wolf channels, they are replaced ureters. Most vertebrates have bladder. In primary aquatics, ammonia can be dumped through the gills.
Sex organs. The sex glands of vertebrates - the ovaries in females and the testes in males - are usually paired. They develop from the mesoderm section at the site of division of this rudiment into the somite and the lateral plate.
Initially (in jawless) the sex glands did not have excretory ducts and the reproductive products fell out through ruptures in the walls of the gonads into the body cavity, from where they were excreted into the external environment through special pores. Subsequently, the genital tract arose, which in males is associated with the excretory organs (Wolf's canal). And in females, it functions as an oviduct Mueller channel, which maintains the connection of the whole with the external environment.
Vertebrate animals include highly organized mobile chordates, characterized by active methods of obtaining food. The notochord in most species is replaced by the spine, the skull and jaws develop, ensuring the capture and retention of food. Paired limbs and their belts appear, allowing animals to move, actively looking for food and escaping from the pursuit of enemies. The high level of their activity is provided by the peculiarities of the morphological and physical organization of the main organ systems.
Thus, the neural tube in vertebrates has a brain and spinal cord, protected by the bones of the skull and spine. The brain includes five sections: anterior, intermediate, middle, cerebellum and oblongata, the functioning of which forms the basis of adaptive behavior. Perfection is achieved by the structure of various sense organs, which allow communication between a living organism and the external environment.
An increase in the level of metabolism in vertebrates is carried out with the help of a differentiated digestive system, developed by powerful digestive glands - the liver and pancreas, which activate the processes of digestion. The appearance of a second, pulmonary circulation, rapid blood flow, large respiratory surfaces and the replacement of the nephridial excretory system by more perfectly functioning organs - the kidneys, which remove an increased amount of decay products from the body - these are the main paths of evolution of vertebrates that led them to progressive development.
The subtype Vertebrates includes the following main classes: Cartilaginous and Bony Fishes, Amphibians, Reptiles, Birds, Mammals.
Superclass Pisces
Classes Cartilaginous (Chondrichthyes) and
Bony (Osteichthyes) fish
General characteristics of fish
This is the largest in terms of the number of species (more than 20 thousand) and the most ancient group of primary aquatic chordates. Fish inhabited all types of marine, fresh and brackish water bodies. Their whole organization bears the imprint of adaptation to life in a dense aquatic environment. The main features of their organization are as follows:
body shape streamlined due to the smooth transition of its departments - the head, trunk and tail - into each other and flattened from the sides.
The skin is rich in glands, abundantly secreting mucus, and covered with scales.
The organs of movement and stabilization of the position of the body with the back up are unpaired and paired fins. The buoyancy of bony fish is maintained by a hydrostatic organ - plawadding bubble.
Skeleton cartilaginous or bone. Scull still connected to the spine. There are two sections in the spine: trunk and tail. Belts limbs are not connected with the axial skeleton.
muscles poorly differentiated, segmented. Body movements are monotonous, serpentine and mostly in the horizontal plane.
Capturing food is active with jaws. The anterior and middle sections of the intestine are strongly differentiated. Developed digestive glands: liver and pancreas.
Respiratory system - gills.
The circulatory system is closed one circle of blood circulationscheniya and bicameral heart. The organs and tissues of fish are supplied with arterial blood.
excretory organs - paired trunk kidneys. The end product of nitrogen metabolism excreted from the body is ammiak or urea.
The central nervous system is represented by the brain and spinnym brain. The brain is differentiated into five sections. The structure of the sense organs - vision, smell, hearing - is adapted to functioning in the aquatic environment. Special lateral line organ allowing the fish to navigate the currents of the water.
The fish are dioecious, many are characterized by sexual dimorphism. Reproduction only sexual. Most fertilization is external, in water. Development with incomplete metamorphosis (with the larval stage).
Features of the structure and processes of life in connection with life in the water
The body sections of the fish - head, body, tail - smoothly pass into each other, providing streamlining (Fig. 33). Fish swim due to the lateral undulating bends of the body. The body is covered with tiled bone plates - scales. Mucus secreted by numerous skin glands reduces friction when the fish moves. Paired fins - pectoral and ventral - support the normal position of the body with the back up, serve as rudders, and in some fish (stingrays) - the main organs of movement.
fish skeleton consists of a skull, spine, skeleton of unpaired, paired fins and their belts. In the trunk region, ribs are attached to the transverse processes of the body. The vertebrae articulate with each other with the help of articular processes, providing bending mainly in the horizontal plane.
Fig 33. Appearance and internal structure of fish (perch): 1 - nostrils; 2 - eyes; 3, 6 - dorsal fins; 4 - kidneys; 5 - swim bladder; 7 - tail fin; 8 - caudal fin; 9 - bladder; 10 - ovary; 11 - intestines; 12 - gallbladder; 13 - liver; 14 - heart; 15 - gills; 16 - mouth.
The skull is formed by a large number of bones and bears jaws equipped with teeth. The skeleton serves as a support for the muscles and protection for the internal organs.
The powerful musculature of fish consists of segments separated by connective tissue septa, and in general resembles the muscular system of the lancelet. Separate bundles of muscles control the movements of the eyes, gills, and jaws.
Rice. 34. Perch skeleton: 1 - spine; 2 - ribs; 3 - cranium; 4 - upper jaw; 5 - lower jaw; 6 - bones of the gill cover; 7 - bones of the pectoral fin; 8 - bones of the ventral fin.
Fish eat a variety of foods. Food specialization is reflected in the structure of the digestive organs. The mouth leads to the oral cavity, which usually contains numerous teeth located on the jaw, palatine and other bones. Salivary glands are absent. From the oral cavity, food passes into the pharynx, perforated by gill slits, and through the esophagus enters the stomach, the glands of which abundantly secrete digestive juices. Some fish (cyprinids and a number of others) do not have a stomach and food enters immediately into the small intestine, where, under the influence of a complex of enzymes secreted by the glands of the intestine itself, the liver and pancreas, food is broken down and the dissolved nutrients are absorbed.
Most fish have a thin-walled outgrowth of the intestine filled with a mixture of gases - swim bladder. It performs a hydrostatic function, i.e. equalizes the density of fish with the density of water, which allows the fish to stay at any depth without muscle effort. The gaseous mixture with which the bladder is filled can be absorbed or released by the capillaries of the bladder walls, which changes the specific gravity of the fish.
Respiratory organs - gills - located on the upper side of the four gill arches in the form of bright red petals. Water enters the mouth of the fish, is filtered through the gill slits, washing the gills, and is brought out from under the gill cover. Gas exchange is carried out in numerous gill capillaries, in which blood flows towards the water surrounding the gills.
On the underside of the gill arches are whitish stamens, which are of great importance in the nutrition of fish: in some they form a filtering apparatus - a device for feeding on fine food suspension, in others they help to keep large prey in the oral cavity.
The circulatory system of fish is closed. The heart is two-chambered, consisting of an atrium and a ventricle. Venous blood from the ventricle of the heart enters the abdominal aorta, which carries it to the gills, where it is enriched with oxygen and released from carbon dioxide. Arterial blood flowing from the gills is collected in the dorsal aorta, which is located along the body under the spine. Numerous arteries depart from the dorsal aorta to various organs of the fish. In them, the arteries break up into a network of the thinnest capillaries, through the walls of which the blood gives off oxygen and is enriched with carbon dioxide. Venous blood is collected in the veins and through them enters the atrium, and from it - into the ventricle. Therefore, fish have one circle of blood circulation.
Fish are animals with variable body temperature. The speed of their vital processes depends on the temperature of the water.
Rice. 35. Scheme of the circulatory system of fish.
excretory organs are paired ribbon-like trunk kidneys located in the body cavity under the spine. They have lost contact with the body cavity and remove harmful waste products by filtering them out of the blood. In freshwater fish, the end product of protein metabolism is toxic ammonia. It dissolves in a lot of water, and therefore the fish excrete a lot of liquid urine. The water excreted in the urine is easily replenished due to its constant intake through the skin, gills and with food. In marine fish, the end product of nitrogen metabolism is less toxic urea, the excretion of which requires less water. The urine formed in the kidneys flows through the paired ureters into the bladder, from where it is excreted out through the excretory opening.
central nervous system consists of the brain and spinal cord. The brain in fish, like in all vertebrates, is represented by five sections: anterior, intermediate, middle, cerebellum and medulla oblongata. Well-developed olfactory lobes depart from the forebrain. The greatest development reaches the midbrain, which analyzes visual perceptions, as well as the cerebellum, which regulates the coordination of movements and maintaining balance.
Mood sense organs strongly influenced by life in the aquatic environment. So, the eyes have a flat cornea and an almost spherical lens, which makes it possible for fish to see only nearby objects (up to 10-15 m). Since natural waters are characterized by low transparency, far vision in fish is not developed. Accommodation, i.e., aiming at a clear vision of an object, is carried out by contraction of the muscular process of the lens, which moves it in relation to the retina.
A sharp sense of smell helps the search for food, the meeting of individuals of different sexes, the ability to stay in a flock of fish. The olfactory organ is a pair of sacs lined with sensory cells, to the base of which the fibers of the olfactory nerve fit. The olfactory sacs open outwards through a hole - the nostrils. The organ of taste is represented by numerous taste buds located on the lips, in the esophagus, pharynx, and even on the fins.
The organ of hearing and balance is represented only by the inner ear, located on the sides of the back of the skull. The speed of sound in water is four times faster than in air. Therefore, the simple structure of the hearing organ of fish allows them to sensitively perceive sound waves through the bones of the skull. Fish are able to make sounds with their teeth, gill covers, fins, swim bladder. Through sound signaling, fish express their emotional state - threat, warning, call, alarm, etc.
plays an important role in the life of fish lateral line organ(Fig. 36). It is represented by longitudinal channels lying on the sides of the body in the skin and communicating with the external environment through a large number of linearly arranged holes. At the bottom of the canals, opposite the openings, there are sensitive cells equipped with cilia. They perceive changes in pressure and direction of water, which makes it possible for fish to freely navigate in its streams, swim successfully both in the daytime and at night and avoid collisions with underwater objects. This organ is present only in primary water, i.e., in fish and amphibians. It reached its greatest development in fish.
Rice. 36. Organ of the lateral line of bony fish: 1 - transverse tubules opening into the external environment; 2 - longitudinal channel; 3 - receptors perceiving water pressure; 4 - nerve.
Reproduction. Most fish are dioecious, however, there are also hermaphroditic species. Paired sex glands - ovaries and testes - have excretory ducts. Fertilization in most fish is external and occurs in water. Preparation for the sexual process and its course itself is accompanied by a complex instinctive behavior of fish - spawning. Many fish species migrate before spawning, moving to places more favorable for the development of their offspring. Thus, anadromous fish migrate from the seas to the rivers (sturgeon, salmon) or from the rivers to the seas (river eel). Some species of fish breed with a certain frequency, others - once in a lifetime (Far Eastern salmon, river eel) and die after breeding.
In some species of fish (guppies, swordtails) live birth is observed. Their fertilized eggs develop in the female's ovary, and the fry feed on her destroyed tissue.
The fertility of fish is different. Fish that do not take care of the offspring, when the probability of the death of eggs is high, lay a huge number of eggs (one female cod and eel have up to 8-10 million), and if there is care for the offspring, the amount of eggs laid by females is significantly reduced (in the three-spined stickleback, only 80 - 1000 eggs).
The egg hatches into a larva with a yolk sac on the ventral side of the body, unable to feed externally for several days. Having exhausted the reserves of nutrients from the yolk sac, the larva switches to feeding on protozoa and small crustaceans and turns into a fry (having scales) and then, after a period of growth, into an adult fish.
Class Cartilaginous fish . This class is represented by a group of few marine fish species that have a cartilaginous skeleton throughout their lives. There are no gill covers; 5-7 gill slits open outward on the sides of the head. The swim bladder is not developed, therefore, in order not to drown, the fish actively swim. The paired fins are horizontal. The caudal fin is unevenly lobed, with large upper and small lower lobes. The anterior part of the head is extended into an elongated snout, which is why the mouth is located on the ventral side and looks like a transverse slit. Fertilization is internal. Reproduction occurs by oviposition or live birth.
Cartilaginous fish belong to two orders: Sharks and Stingrays. sharks mostly active swimmers with torpedo-shaped bodies. Most of them are predators, finding prey with the help of smell, as well as the perception of water vibrations by the lateral line organ. The jaws are armed with sharp teeth. The largest species feed by straining plankton.
stingrays have a flattened body in the dorsal-abdominal direction with greatly enlarged pectoral fins. Gill slits are located on the ventral side. Teeth in the form of low prisms, collected in a "grater". They feed on fish and bottom animals. The meat of sharks and rays is edible.
Class Bony fish . This is the most numerous group of vertebrates (over 19 thousand species). The internal skeleton is bony, in a few cartilaginous, but in the latter case it is reinforced with overhead integumentary bones. The gill slit is covered from the sides by the gill cover. There is a swim bladder. Fertilization is mainly external. There are more than 40 teams in the class.
To order Sturgeons belong to the beluga, sturgeon, stellate sturgeon, sterlet and other ancient bony fish. Like cartilaginous fish, they have a snout, a mouth in the form of a transverse slit on the ventral side of the body, horizontal paired fins, and a tail with an enlarged upper and smaller lower lobes. The basis of the axial skeleton is cartilage. The skull is covered with flat bones on the outside, and five rows of bone rhombic plates are located on the body and tail. They live only in the Northern Hemisphere, they are anadromous and lake-river fish. They feed on benthic invertebrates and fish. These are valuable commercial fish that provide high-quality meat and black caviar.
Order Herring includes marine schooling planktivorous fish. Most of them live near the coast. They lay numerous sticky eggs on the ground or algae. The detachment is rich in commercial fish: Atlantic, Pacific herring, Baltic (herring), sardines, anchovies.
Order Salmonformes It is represented by anadromous and freshwater fish that lay their eggs on the bottom of freshwater bodies of the Northern Hemisphere. A distinctive external feature of the salmon structure is the presence of an adipose fin (without bone rays). They lay a small number of large red eggs. Salmon - valuable commercial fish (chum salmon, pink salmon, brown trout, salmon; trout, char, vendace), giving high-quality meat and red caviar.
Order Cyprinidae unites freshwater fish that do not have jaw teeth. Food is crushed by pharyngeal teeth. These include commercial fish - roach, bream, tench, carp, ide, etc. Carp (the domestic form of carp), silver carp, tench, white and motley silver carp, grass carp, etc. are bred in the pond farms of our republic.
Squad lungfish refers to the oldest fish that have adapted to life in the conditions of drying water bodies of Africa, Australia and South America. In addition to the gills, they breathe with one or two lungs - hollow outgrowths of the abdominal wall of the esophagus. Air enters the lungs through the nostrils. The formation of the second atrium and the pulmonary circulation is outlined. Representatives of this order are the Australian horntooth, the American flake.
Detachment of the Crossoptera is also an ancient and almost completely extinct group. The heyday of the crossopterygians reached in the Devonian and Carboniferous. Currently, only one species is known - coelacanth, which lives in the depths of the Indian Ocean. The length of the fish is up to 1.5 m. It has paired fins in a peculiar way. At their base is a wide fleshy lobe, inside which is the fin skeleton, resembling the limb skeleton of terrestrial vertebrates. The lobe-finned fish are a branch of fish from which amphibians originated.
Fish and fish products play an important role in human life. The annual global catch is about 60 million tons. In the global balance of animal proteins, the value of food products produced from fisheries is close to 22% second only to meat (43%) and dairy (35%) products. The main part of the catches (about 90%) falls on shallow water zones with depths up to 200 m.
The leading role in the world fish production belongs to herring (22%), cod (17%), mackerel (6%), and horse mackerel (6%).
In recent years, the growth of the fish catch has stopped. This is the result of the depletion of stocks of many species due to overfishing, poisoning with salts of heavy metals, destruction, pollution of spawning grounds, etc. The time is coming for a gradual transition to human-controlled marine fisheries, i.e. the transition from fishing-hunting to growing commercial objects. The role of bred and cultivated fish will increase every year.
The greatest success in breeding freshwater fish has been achieved in pond farms, which have a long history of development. Their characteristic feature is the complete human control over the technological chain of fish rearing from larva to marketable products. Depending on the purpose, feeding, nursery, wintering and some other types of artificial ponds are distinguished. Spawning ponds are designed for fish spawning. They are small in size, well warmed up, their bed is covered with soft meadow vegetation. From the spawning ponds, the grown and strengthened larvae are transplanted into larger and deeper nursery ponds, where underyearlings grow up by autumn. For the winter, underyearlings are transferred to deep flowing small wintering ponds. In the spring of the next year, yearlings from wintering ponds are placed in feeding ponds, in which they grow to marketable weight. The main objects of fish farming are carp, white and motley carp, grass carp, pike, crucian carp, etc. Trout is an object of cold-water fish farming.
Test questions:
What common features of organization are common to all Chords?
What are the structural features of the Skullless (for example, the lancelet)?
What are the structural features of vertebrates?
What are the adaptations of fish to life in the aquatic environment?
What features of the structure of the circulatory system appeared in fish?
What is the reason for the complexity of fish behavior? Which organ system is responsible for this?
What structural features are inherent in cartilaginous fish?
What is the practical importance of fishing and fish farming in human economic activity?
Class Amphibians, or Amphibians ( Amphibia )
