Chordates and humans are common characters. Signs of chordates. General characteristics of the chordate type

In this article, we will consider in detail the question of what features are common to chordates. Representatives of this type are distinguished on the basis of a number of characteristic features. Let's take a look at the main ones.

So, what features are common to chordates? Let's start with bilateral symmetry. This sign is one of the most important.

Bilateral symmetry

All chordates are characterized by bilateral (bilateral) symmetry. The same structure is characteristic of other types of multicellular animals, starting with the lower worms. Bilateral symmetry reflects an important moment in the evolution of multicellular organisms. The transition to active movement in the environment is potentially associated with the intensification of nutrition and the level of metabolism, the diversity of life forms and the expansion of the range of biotopes available for permanent habitation.

Secondary body cavity (general)

The second major stage in the evolution of animals was the formation of a secondary body cavity (coelom). This stage begins with annelids. biological significance secondary body cavity is associated with further activation of movement and nutrition. In cavitary and primary cavitary animals, the intestines are surrounded by loose parenchymatic tissue or fluid, the movement of food in the digestive tract is carried out by contractions of the skin-muscular sac, which simultaneously cause and forward movement the whole organism. In other words, the contractions of the entire trunk and intestines are synchronized, which is not always biologically beneficial for the effective assimilation of food.

The emergence of a secondary body cavity, which separates the intestines and the skin-muscle sac, and the appearance of the intestinal musculature, which is formed from the mesoderm, open up the possibility of intestinal motility independent of locomotion. Each of these important functions - movement in space and digestive activity - is carried out depending on environmental requirements, does not limit each other. In this case, the whole can also play a supporting role, acting as a "hydroskeleton".

No less important is another function of the coelom - transport. Its outgrowths, penetrating deep into the tissues, provide them with nutrients and oxygen. On the basis of outgrowths of the intestine, the circulatory system is formed. They are connected with the coelom and thus, on the basis of the secondary cavity of the body, exchange is maintained at the tissue and organ level.

All chordates belong to the secondary cavities, which phylogenetically connects them with such types as bryozoans, brachiopods, arthropods, echinoderms, pogonophores, etc. The secondary cavities originate from the ancient intestinal cavities.

recurrence

Considering the general signs of chordates, it is necessary to note the secondority. All celiac organisms fall into two branches: protostomes and deuterostomes. The names of the groups are associated with the peculiarities of embryonic development: in the former, the position of the oral opening corresponds to the blastopore, which is divided into the mouth and anus, and in the latter, the blastopore takes on the functions of the anus, and the mouth erupts elsewhere. This group includes hemichordates, echinoderms, pogonophores and chordates. All other types of deuterated animals are classified as protostomes.

But the differences between these groups are more significant than the position of the mouth opening. First of all, they differ in the nature of the formation of the coelom: in most protostomes, the coelom is formed schisocoelally (by splitting the mesenchyme), and the mesoderm arises by migrating cells from adjacent tissues into this cavity (teloblastic type). In deuterostomes, the whole is enterocelous, it develops by paired protrusions of the intestine: their walls give rise to a mesodermal sheet. In addition, protostomes are also characterized by a "ladder" type of structure of the central nervous system, while in deuterostomes the circulatory system is overwhelmingly closed, and the central nervous system has a different structure, in which large clusters of nerve cells often form in some places.

Specific features of chordates

In addition to the listed features, characteristic of all chordates, but also found among other animals, representatives of the type of interest to us also have some specific structural features. We will consider the main ones in detail below.

Chord

All chordates have an internal main element of which is the chord. It is an elastic cord composed of vacuolated cells that form a cartilaginous tissue of endodermal origin. The notochord is surrounded by a sheath of connective tissue. Its main function is support; the axial skeleton helps to maintain the shape of the body. A close relationship with the surrounding axial muscles and a certain degree of mobility and elasticity determine the participation of the chord in the lateral bends of the body, creating in a dense aquatic environment.

The notochord, as the only structure of the axial skeleton, exists only in the lower representatives of the type; in most vertebrates, it is laid down in the embryonic period of development, but later it is replaced by the spine, which is formed in its connective tissue membrane. In biology tests, the question is often asked: "What features are common to chordates and fish?". One of the correct answers is "the presence of a chord". In fish, the spine later assumes all its functions (including locomotor), and in terrestrial vertebrates, it is mainly supporting; its direct participation in locomotion is replaced by the function of support for individual parts of the motor apparatus.

The tubular structure of the central nervous system

The central nervous system in the form of a tube with a cavity inside is a strictly specific feature. Due to the fact that the neural plate laid down from the ectoderm in further embryogenesis folds into a tube, a cavity formed inside the spinal cord formed in this way arises - a neurocoel (spinal canal), filled with cerebrospinal fluid.

We have not yet considered all the signs of chordates. Let's talk about one more thing.

Gill slits

A characteristic feature of the representatives of the type of interest to us is that the anterior section of the intestinal tube of these animals is permeated with gill slits - openings connecting the pharyngeal cavity (as this section is called) with the external environment. The appearance of gill slits is associated with the filtering nature of nutrition: water is ejected through them after the separation of food particles that enter the intestine.

Finally

So, we talked about what features are common to chordates. Based on them, as well as some other characteristics, representatives of this type are distinguished from others. It is necessary not only to memorize, but also to understand the general signs of chordates. The table below contains information on which subtypes and classes all of its representatives are divided into.

We hope the material presented in this article has helped you understand the features of this type.

This is the most highly organized group of animals that have mastered various habitats. Modern type classification:

Subtype Cranial (Acrania)

Subtype Larval-chordata (Urochordata)

Subtype Vertebrates (Vertebrata)

Section Jawless - Agnatha

Superclass Jawless - Agnatha

Class Cyclostomes - Cyclostomata

Section Jaws - Gnathostomata

Superclass Pisces - Pisces

Class Cartilaginous fish - Chondrichthyes

Class Bony fish - Osteichthyes

Superclass Tetrapoda, or Terrestrial vertebrates - Tetrapoda

Class Amphibians, or Amphibians - Amphibia

Class Reptiles, or Reptiles - Reptilia

Bird Class - Aves

Class Mammals, or Animals - Mammalia

All chordates have an internal skeleton , the main axial element of which is a chord . The notochord arises from the endoderm and is an elastic cord formed by large vacuolated cells. Outside, the notochord is dressed by a connective tissue sheath. The notochord serves to support the muscles and is involved in the movement of the animal. Throughout life, the notochord is preserved only in the lower representatives of the type. In vertebrates, the notochord is present in embryonic development and is then replaced by the spine. The spine performs the same functions as the chord.

The central nervous system of chordates has a tubular structure. The neural tube is formed from the ectoderm and is located above the notochord. Inside it there is a channel called neurocoel.

In the anterior part of the digestive tube, chordates have gill slits. Gill slits connect the pharyngeal cavity with the external environment. In aquatic vertebrates (fish), gills are formed in the gill slits - the organs of water respiration. In terrestrial vertebrates, gill slits are present only in embryos on early stages individual development.

In the abdominal part of the body, under the digestive tube is the heart, from which the blood moves in the anterior direction.

Chordates are bilaterally symmetrical animals, deuterocavities, deuterostomes.

To the question of common features of the chordate type, asked by the author Begimai Usonova the best answer is Despite the huge diversity, all representatives of the Chordata type are characterized by common features of organization that are not found in representatives of other types. Consider the main features of the type using an interactive scheme:
The body is bilateral - symmetrical.
Intestine through.
Above the intestines is a chord.
Above the chord, on the dorsal side of the body, is the nervous system in the form of a neural tube.
The walls of the pharynx have gill slits.
The circulatory system is closed. Heart on the ventral side of the body, under the alimentary canal.
They live in all environments.
Source: biology

Answer from lady by the fireplace[guru]
The chordate phylum is subdivided into three subtypes: non-cranial, tunicates, and vertebrates. Despite the great variety of species, the body of all chordates has overall plan structure and consists of a head, trunk, tail and limbs. The main feature of representatives of the type is the presence (at least at one of the stages of individual development) of a chord - a flexible, elastic cord that acts as an axial skeleton. The notochord is located above the intestine and is formed from the endoderm by splitting off a cell cord from the dorsal side of the intestinal tube.
Despite the exceptional diversity of chordates, they all have a number of common structural and developmental features. The main ones are:
1. All chordates have an axial skeleton, which initially appears in the form of a dorsal string, or chord. The notochord is an elastic, non-segmented strand that develops embryonically by lacing it from the dorsal wall of the germinal gut: the notochord is of endodermal origin. The subsequent fate of the chord is different. It persists for life only in lower chordates (with the exception of ascidia and salps). In most representatives, the notochord is reduced to one degree or another in connection with the development of the spinal column. In higher chordates, it is an embryonic organ and in adult animals it is to some extent replaced by vertebrae, in connection with this, the axial skeleton from a continuous non-segmented cord becomes segmented. The spine, like all other skeletal formations (except the notochord), is of mesodermal origin and is formed from a connective tissue sheath surrounding the notochord and neural tube.
2. Above the axial skeleton is the central nervous system of chordates, represented by a hollow tube. The cavity of the neural tube is called the neurocoel. The tubular structure of the central nervous system is characteristic of almost all chordates. The only exceptions are adult tunicates. In almost all chordates, the anterior neural tube grows and forms the brain. The internal cavity is preserved in this case in the form of the ventricles of the brain. Embryonally, the neural tube develops from the dorsal part of the ectodermal bud.
th. In lower forms, gills are located on their walls. Gill slits are preserved for life only in lower aquatic chordates. For the rest, they appear only as embryonic formations, functioning at some stages of development or not functioning at all.
Along with these three main features of chordates, the following should be mentioned. character traits their organizations, which, however, besides the chordates, are also found in representatives of some other groups. Chordates, like echinoderms, have a secondary mouth. It is formed embryonically by breaking through the gastrula wall at the end opposite the gastropore. In place of the overgrown gastropore, an anus is formed. The body cavity in chordates is secondary (as a whole). This feature brings chordates closer to echinoderms and annelids.
The metameric arrangement of many organs is especially pronounced in embryos and lower chordates. In their higher representatives, due to the general complication of the structure, metamerism is weakly expressed.
Chordates are characterized by bilateral (bilateral) symmetry of the body. As is known, in addition to chordates, many groups of invertebrates have this feature.
Evolutionarily, chordates are characterized by morphophysiological continuity in all organ systems, which can be traced in the change in homologous organs.

Answer from Yana[guru]

Answer from Ivan Yarish[guru]
. All chordates have an axial skeleton or notochord.

3. The anterior (pharyngeal) section of the digestive tube communicates with the external environment by two rows of holes, called visceral slits

Answer from Nikita Shurshilin[newbie]
All chordates have an axial skeleton or notochord.
2. Above the axial skeleton is the central nervous system of chordates, represented by a hollow tube. In almost all chordates, the anterior neural tube grows and forms the brain.
3. The anterior (pharyngeal) section of the digestive tube communicates with the external environment by two rows of holes, called visceral slits
the presence of a chord instead of a spine. lack of bones

Chordates on Wikipedia
Check out the wikipedia article on Chordates

Chordates include about 40 thousand different species of individuals that differ from others in structure, lifestyle, and habitat.

The Paleozoic era contributed to the appearance of this type of animal about 500 million years ago. Scientists suggest that their ancestors were annelids.

Chordates settled all over the planet and became habitual inhabitants of the sea, land, air and even soil.

What is a chord and who are chordates

The internal structure of chordates is different from others. They are characterized by the presence of an axial skeleton - the spinal column, which is otherwise called the chord.

It is this feature of the structure of the spine that gave the name to chordates.

Structural features

The following features are characteristic of chordates:

1. The location of the neural tube above the axial skeleton and the formation of the spinal cord from it.
2. The presence of a rod - a chord.
3. Absence of intestines in the caudal region.
4. Location of the heart under the digestive tract.

Type Chordates (chordata) - examples of animals

Representatives of chordates:

Origin and evolution of chordates

Biology as a science considers the origin of chordates one of the most important stages of development historical world animals.

The emergence of this type meant the emergence of new animals with a unique structure, which allowed them to further evolve to creatures with maximum complexity in structure and behavior.

Some scientists believe that chordates began to exist even before the appearance of annelids, which fed by filtration. Other scientists attribute them to the ancestors of chordates.

One way or another, but the evolution of annelids, or, as they are also called, bottom worm-like animals, gave birth to new types: echinoderms, pogonophores, hemichordates and chordates.

Subsequently, chordates evolved in three directions, depending on the lifestyle:

1. The habitat of individuals of the first direction was hard ground. This contributed to the active development of the filtering apparatus, which provides nutrition during a sedentary lifestyle, and the formation of a thick protective shell on the entire surface of the body. These individuals have the ability to reproduce asexually. This is how shellers appeared.
2. The habitat of individuals of the second direction is the bottom. They moved a little more, digging into the ground. This way of life simplified their original organization. The development of the myochordial complex required increased mobility, and the expansion of the pharynx added new gill slits. This branch has survived to this day in the form of non-cranial.
3. The habitat of individuals of the third direction, which began to lead a floating lifestyle, is fresh water. There was a transition to active nutrition, increased mobility. The nervous system and sense organs became more perfect, which led to the complication of behavior and the emergence of more complex forms. Thus, a group of vertebrates appeared.

in rivers and other fresh waters the jawless ones also formed, from which the jawed ones later separated. They expanded their habitat into salt water and became the progenitors of modern fish groups.

Later, amphibians separated from the fish. Then they landed, and thus appeared the new kind- reptiles.

General characteristics of the chordate type

The cover consists of two layers of leather. The upper layer is represented by the epidermis and its derivatives: scales, feathers, wool, hair. In this layer of the skin are odorous glands that produce mucus and sweat. The bottom layer is the dermis, which is made up of fibrous connective tissue.

The musculoskeletal system is presented in the form of a skeleton, consisting of a chord and a membrane connecting the tissues. The skeleton of the head is divided into brain and facial parts.

Fish develop jaws, while vertebrates develop two pairs of limbs. Bones are connected by joints.

Respiratory system in lower chordates, it is represented by gills, and in vertebrates, by lungs. In addition, the skin of chordates is partially involved in gas exchange.

The digestive system in cephalochords is a straight tube and almost undeveloped digestive glands. In vertebrates, this is the alimentary canal, which has sections.

First, food enters oral cavity, then passes into the pharynx, begins to be processed in the esophagus, passes into the stomach and, finally, enters the intestines. In addition to these organs, vertebrates have a liver and pancreas.

The circulatory system is closed. In vertebrates, due to the increase in the intensity of metabolism, the heart appeared and became more complicated. Cephalothordates have no heart.

In birds, the heart differs from the heart of reptiles only in the presence of a complete septum and the absence of the left aortic arch; mammals have a four-chambered heart that pumps two types of blood: arterial and venous.

The central nervous system (CNS) of chordates has the form of a neural tube with an internal canal, which in vertebrates forms the brain. The peripheral nervous system consists of cranial and spinal nerves that branch off from the central nervous system.

The excretory system in all chordates, except for lancelets, is represented by paired kidneys, ureters and bladder.

Reproductive system: reproduction occurs with the help of testes in males and ovaries in females. Tunicates are hermaphrodites, they reproduce both sexually and asexually. The rest of the chordates have a sexual division.

Classification of chordates and their subtypes

Chordates are divided into lower (lamprey, lancelet, hagfish) and higher (reptiles, amphibians, fish, birds, mammals).

The following subtypes are distinguished:

• non-cranial;
• tunicates;
• jawless;
• primary water: classes of fish;
• tetrapods: classes of amphibians or amphibians, reptiles or reptiles, birds, mammals.

What signs of chordates does a person have

In humans, like chordates, in the early stages of development, the formation of an axial skeleton, that is, a chord, occurs. The musculoskeletal system in humans is represented, as in vertebrates, by the supporting internal skeleton.

Man also has the following features of chordates:

• the central nervous system, which has a tubular structure;
• a closed circulatory system with the main organ of blood circulation - the heart;
• breathing apparatus capable of communicating with the external environment through the pharynx, nasal cavity and mouth.

monkey eel

Some interesting information:

The value of chordates is very great, they are classified as the most diverse and numerous types. On the this moment there are about 50 thousand species of chordates. Availability common feature in all individuals - chords (supporting organ) gave the name to this type of animal.

Anatomical signs of chordates are similar to echinoderms. The lower representatives of chordates are lancelets, which retain their main feature throughout their lives.

LECTURE COMPLEX (THESES OF LECTURES, ILLUSTRATIVE AND HANDOUT MATERIAL; LIST OF RECOMMENDED LITERATURE)

CARD OF EDUCATIONAL AND METHODOLOGICAL SUPPORT OF THE DISCIPLINE

Bibliography

Table 1

3.2. Methodological support of discipline(Guidelines for standard calculations, performance of calculation and graphic, laboratory work, course projects (works), etc.)

table 2

3.3. List of specialized tools(rooms and laboratories, equipment, reagents, models, stands, real-virtual laboratories, software products, etc.) used in teaching the discipline. Software and multimedia support of training sessions.

Table 3

Start your self-preparation by studying the syllabus of the discipline, select the recommended literature.

Reading the proposed sources, make notes and notes on individual issues in your notebook, in some cases make a plan or short text response. This will help you remember the question when preparing for the exam.

Detailed practice plans can be found at electronic library on the EHF website by selecting your group and EMKD "Ecology of Plants, Animals and Humans".

Tasks for IWS should be performed in a separate notebook, attach to it the texts of speeches (reports), which, after the control of the teacher and his recommendations, can be used by students in the course of the further learning process, in the course of teaching practice.

Topic: Introduction to vertebrate zoology

1. Deuterostomes, the body cavity is secondary (as a whole)

2. The circulatory system is closed, the blood is oxidized in specialized respiratory organs (gills or lungs)

3. Body with bilateral symmetry

4. The body is more or less composed of metameres

5. A chord runs along the entire body; some have it only at the larval or embryonic stage of development

6. Higher ones have a cartilaginous or bone skeleton

7. The pharynx is pierced by gill slits in many only at the embryonic stage of development

8. Central nervous system in the form of a tube, located above the chord

Classification

chordates

non-cranial

TUNICATA (UROCHORDATA)

CRANIOTA (VERTEBRATA)

cranial (vertebral)

non-cranial

cephalochordates

lanceolate

Branchiostomidae Epigonichtidae Amphioxididae

Families:

tunicates (larval chordates)

TUNICATA (UROCHORDATA)

appendiculars

cranial (vertebral)

CRANIOTA (VERTEBRATA)

jawless

jawed

(and modern lampreys)

extinct corymbs

Pteraspidomorphi

(extinct)

Cephalaspidomorphi

(extinct)

armored fish

(extinct)

maxillofabral

(extinct)

cartilaginous fish

bony fish

amphibians

parareptiles

reptiles

mammal

subject: general characteristics non-cranial

The lancelet is a representative of the skullless, most primitive chordate animals. All the main features of the chordate type in non-cranial are well expressed and persist for life. The notochord functions as an axial skeleton, the central nervous system is represented by the neural tube, the pharynx is pierced by gill slits.

There is a secondary mouth and a secondary body cavity - the whole. Metamerism is preserved in a number of organs. Non-cranial animals are characterized by bilateral (bilateral) symmetry of the body. These signs point to the phylogenetic relationship of the non-cranial with certain groups of invertebrates (annelids, echinoderms, etc.).

In addition, non-cranial, and in particular the lancelet, are characterized by a number of specific primitive features that distinguish them well from other chordates. These differences are as follows.

The epidermis is single-layered, covered with a thin cuticle. The cutis is weakly expressed and is represented by a thin layer of gelatinous tissue. The central nervous system is not differentiated into the head and spinal cord. Due to the lack of a brain, there is no skull.

The sense organs are poorly developed: there are only tactile cells with sensitive hairs (these cells are scattered over the surface of the body) and light-sensitive formations - the eyes of Hesse, located in the walls of the neural tube.

The gill slits do not open outwards, but into the atrial, or peribranchial, cavity resulting from the fusion of the lateral (metapleural) skin folds. The digestive system consists of a poorly differentiated tube, in which only two sections of the pharynx and intestine stand out.

At the bottom of the pharynx there is a longitudinal groove - endostyle lined with ciliated epithelium and glandular cells. At the mouth opening, the endostyle bifurcates and, bending around it on both sides with two grooves, rises to the upper side of the pharynx, where it passes into the supragillary groove directed towards the intestine. The function of the endostyle is to extract food particles from the water. The latter, getting along with the flow of water into the pharyngeal intestine, settle to the bottom of the pharynx, are enveloped in mucus, which is secreted by the glandular cells of the endostyle, and are driven forward by the ciliated epithelium to the mouth opening. Here, lumps of food rise along the perioral grooves to the supra-gill groove and are transported along it to the intestine.

The blood of the lancelet is colorless, the heart is missing.

The excretory organs are represented by metamerically located nephridia - short tubes, which in the amount of 90 pairs are located above the pharynx. Each tubule, at one end, opens with several holes - nephrostomy as a whole, and at the other - with one hole into the atrial cavity. Nephrostomes are dressed with special club-shaped cells - solenocytes, inside of which there is a tubule with a ciliated hair included in it. The excretion products are excreted through the nephridia into the atrial cavity directly from the coelom.

The reproductive organs - the testes and ovaries are similar in external structure and are rounded bodies. They are located in the gill section of the skull. Sexual products are excreted into the atrial cavity through the temporarily emerging lolovy ducts.

Skullless - exclusively marine animals. They spend most of their time burrowing into the sandy bottom. They feed passively, extracting food particles from the water, which is driven by the movement of the tentacles through the throat of the animal.

A similar lifestyle is ensured in modern non-cranial animals by a number of morphological adaptations. In the epithelium there are special unicellular glands that secrete mucus, which protects the integument of the lancelet from mechanical damage when buried in the ground. Relatively large muscles and the landet-like shape of the tail contribute to successful digging into the ground. The atrial cavity mentioned above protects the respiratory apparatus from clogging with soil particles. Numerous gills the slits ensure the passage of a large amount of water through them, which is necessary for the breathing of an animal half buried in the sand.The presence of an endostyle in the pharynx and the initial movement of mucus along it towards the flow of water help to more quickly and completely remove food from it, which is very important with a passive method of feeding.

Topic: Characteristics of cyclostomes

The elongated eel-like body is dressed in smooth mucous skin and has only unpaired fins (supported by cartilaginous rays). The skeleton has neither ribs nor limb skeleton; the skeleton of the head consists of a cartilaginous, membranous box from above, dressing the brain and capsules associated with it, surrounding the organs of hearing, sight and smell, cartilage that serve as a support for the mouth and palate, and a cribriform box that dresses the gill apparatus (the back of it surrounds the heart).

The skeleton of the body consists of a dorsal string (Chorda dorsalis), dressed in a double elastic membrane and on the outside with a layer of connective tissue (skeletal layer); in which paired cartilages develop on the upper side, corresponding to the arches of the vertebrae, and unpaired, corresponding to the spinous processes; in the tail region, the same cartilages are also found on the underside of the chord.

The brain is poorly developed, there are no large sympathetic trunks, the sense organs represent an extremely primitive structure (the eyes of some in the larval period or throughout life are hidden under the skin, the nasal cavity of hagfishes opens into the mouth).

The round, funnel-shaped mouth is armed with horny teeth; the same teeth are also found on the tongue, which plays the role of a piston when sucked to underwater objects (or the body of prey). The gill apparatus consists of 6-7 gill cavities lying on the sides of the esophagus and communicating with the esophagus on one side, and with the external environment on the other. In contrast to all other fish, in which water enters and exits through the mouth when breathing, here water enters and exits independently of the mouth opening, which allows these animals to breathe while sucking with their mouths.

The intestine has a spiral fold of mucous membrane.

The circulatory organs are arranged according to the same type as in other fish (see); the heart consists of 1 atrium (preceded by the sinus venosus) and 1 ventricle (followed by the conus arteriosus with 2 valves).

The organs of excretion - the kidneys - are of a very primitive structure. Genital organs in the form of an unpaired gland in myxines on the right side of the body cavity, in lampreys in the midline.

Mature sexual products fall into the body cavity, from where they are removed through a special opening into the urogenital sinus, which lies behind the anus. In hagfish, according to some studies (Nansen and others), in the gonad, male reproductive products (semen) develop first in the posterior half of the gland, and then eggs in the anterior part of the gland. Eggs undergo complete crushing, in some development is associated with transformations (in lampreys). 2 families with 6 genera and 17 species.

Family lamprey(Petromyzontidae) is distinguished by the following features: a mouth with fleshy lips, without filiform appendages (whiskers) on the edge, the nasal cavity has no communication with the oral cavity, the gills open outwards with seven holes on each side, and into the esophagus - one common hole; clear eyes; 4 genera with 12 species. They are found in rivers and seas off the coast in temperate zones, some species for spawning come from the sea into the rivers. They feed on the meat and blood of fish (living or dead), which they stick to, as well as various small invertebrates. From small eggs in lampreys, worm-like larvae emerge with a toothless mouth opening equipped with an upper and lower lips, eyes hidden under the skin and a dorsal fin, directly passing into the tail. Gill sacs open into the esophagus with separate openings. They live in sand and silt, feed on various animal substances and gradually turn into an adult animal. The only European genus of lamprey (Petromyzon) with 2 dorsal fins, of which the posterior passes into the caudal, and numerous small short outgrowths along the edge of the mouth; tongue with serrated teeth, on the upper side of the mouth (in place of the upper jaw) 2 adjacent teeth or transverse plate. Found in the northern temperate zone.

sea ​​lamprey(R. marinus) reaches a length of 1 m and a weight of more than 1.5 kg (up to 3). There is a large gap between the dorsal fins; see the features of the mouth armament in Fig.; the color is yellowish-white or gray, on the back and sides with a black-brown or olive-green pattern. Found off the coast of Europe North America and West Africa, and comes across in the Baltic Sea. For spawning enters the rivers; meat is valuable.

Topic: Characteristics of cartilaginous fish

In elasmobranch fish, which include sharks and rays, bone tissue is completely absent. They have a cartilaginous skeleton, which is often calcified. The upper jaw is represented by a massive palatine-square cartilage that does not merge with the cranium and is connected to it only by connective tissue ligaments or articulations of cartilage. The skin of elasmobranchs is usually covered with placoid scales, which is the most ancient type of scale cover. Each such scale consists of a main plate, on which a conical or mushroom-shaped tooth (skin tooth) rises, covered with a layer of enamel and ending in one or more points. The presence of skin teeth gives the skin of sharks a more or less pronounced and sometimes very strong roughness, due to which it can be used in carpentry as an abrasive. Modified skin teeth form fin spines in horned and prickly sharks, tail spines in stingrays, sawtooth teeth on the snout (rostrum) in saw sharks and saw fish. The jaw teeth, composed of dentine and covered with enamel on the outside, also represent a modification of the placoid scales. The shape of the teeth in elasmobranchs can be very diverse. They are flat triangular or pointed conical, tuberous or awl-shaped, smooth or serrated, single-topped or with additional tops. The teeth are located on the jaws in straight and oblique rows, and in each straight row (from the edge of the jaw to its inner part) there are teeth of several generations. Usually only the front row functions (sometimes several front rows), the remaining teeth are bent inward and replace the front ones as they wear out.

There is never a gill cover in elasmobranch fish, and 5-7 gill slits open outward on each side of the body. Many fish also have splashes - small holes located behind the eye and representing a vestige of another gap between the jaw and hyoid arches. Gill filaments in sharks are plate-shaped and attach to arches along their entire length (hence the name "plate-gill fish"). The presence of a spiral valve in the intestine and an arterial cone in the heart are important anatomical features of elasmobranchs. The spiral valve is an outgrowth of the mucous membrane of the digestive tract. It forms from 4 to 50 turns and greatly increases the absorption surface of the intestine. arterial cone- a special section of the heart, located in front of the ventricle and equipped with several rows of semilunar valves. He is capable of independent rhythmic contractions. The osmotic pressure of the internal environment in elasmobranch fish is provided mainly by urea dissolved in the blood. In this case, there is hypertension of the abdominal fluids in relation to the external environment. In connection with this feature, fresh shark meat, as a rule, does not have a particularly pleasant specific smell, which disappears with appropriate cooking.

The process of reproduction of elasmobranchs is characterized by specific features. Fertilization occurs inside the body of the female, and males therefore have two copulatory organs called pterygopodia. With their help, sperm is introduced into the cloaca of the female. The pterygopodium is a modified posterior part of the ventral fin and has an external groove. The fecundity of elasmobranchs is low, but their eggs have very large reserves of nutrients. Reproduction occurs by oviposition, ovoviviparity or live birth. In oviparous species, a fertilized egg, descending through the oviduct, passes through the protein and shell glands and is dressed in shells that form a hard shell. The egg is then laid on the bottom. Ovoviviparous species, to which most of the modern sharks belong, are characterized by the fact that the fertilized egg remains in the posterior part of the oviducts (in the "womb") until the birth of juveniles. At the same time, some stingrays have a peculiar feeding of developing embryos: the walls of the "womb" form outgrowths that penetrate into the oral cavity of the embryos and secrete a nutrient fluid, somewhat reminiscent of milk. Finally, in viviparous sharks, in which the development of the embryo also occurs in the "womb", there is even a semblance of a child's place (placenta), which serves to nourish the embryo at the expense of maternal blood. In any case, newborn shark-like fish are born quite prepared for independent existence. The body shape of elasmobranch fish is very diverse. Some of them have a torpedo-shaped body, adapted for rapid movement, and are good swimmers, others are flattened in the dorsal-abdominal direction, and usually spend their lives lying on the bottom. Their sizes fluctuate greatly: the smallest species do not exceed 15-30 cm in length, while in giant sharks and rays, the length reaches 15-20 m, and the weight is measured in tons.

The first elasmobranch fish appeared in the ancient seas as early as 300 million years ago, starting from the middle of the Devonian period. Modern elasmobranchs arose later, but many of the living families have existed since jurassic, i.e. at least 150 million years. However, so far sharks have successfully competed with teleosts without showing any signs of extinction. The classification of modern elasmobranchs, of which there are now about 600 species, is based mainly on the signs of the external structure and some features of the anatomy. Usually, two large groups are distinguished - the superorder of sharks (Selachomorpha) and the superorder of rays (Batomorpha). Elastobranchs are a predominantly marine group of fish that flourishes in tropical waters. Their commercial value is relatively small, although they are mined in many areas. The total catch of elasmobranchs (sharks and rays) now reaches about 1% of the total annual catch of marine fish.

Topic: Characteristics of bony fish

Bony fish, like cartilaginous fish, have paired limbs - fins, a mouth formed by grasping jaws with teeth on them, gills are located on gill arches with internal skeletal support, nostrils are paired, and there are three semicircular canals in the inner ear. Unlike cartilaginous fish, there is bone tissue in the skeleton of bony fish; a swim bladder is located in the upper part of the body cavity; the gill cavity is covered by the gill cover reinforced by the bone skeleton; the gills are in the form of freely hanging petals, and not plates adhering to the intergill septa. The body is covered with bony scales, plates, or naked instead of a cover of tooth-like placoid scales.

Among bony fish there are giants and dwarfs - from freshwater beluga, kaluga, catfish, Brazilian arap-ima and marine swordfish and marlin reaching 5-7 m in length and 500-1500 kg in weight to tiny Philippine gobies, 7-11 mm in length .

On the sides of the body and on the head, the pores of the lateral line are usually noticeable - an organ of a special, peculiar only to aquatic animals, sense of perception of water movements. Thanks to the lateral line, even a blinded fish does not run into obstacles and is able to catch moving prey.

The mouth of a fish is usually armed with teeth; teeth are not only on the jaws, but often also on the palatine bones, on the vomer, on the tongue, on the bones of the gill apparatus (pharyngeal teeth). The sides of the pharynx are reinforced with five pairs of bony gill arches, along the inner edge of which are hard gill rakers, and along the outer edge are gill petals abundantly supplied with blood. Through 4 pairs of slits between the gill arches, the fish actively passes water, filtering it through the gratings of gill rakers and gill filaments. With the help of the former, crustaceans and other organisms that serve as fish food are retained in the pharyngeal cavity and enter the esophagus, while in the gill filaments, the passing blood is oxidized by extracting the oxygen dissolved in it from the water washing them. The gills serve as the respiratory organ of the fish. The intestine is usually relatively poorly differentiated into sections: blind outgrowths are specific for fish - pyloric appendages (from 1 to 200), opening at the beginning of the middle intestine, immediately behind the stomach; primitive fish, such as sturgeons, have a spiral fold in the large intestine, like sharks and rays. Adjacent to the intestine is the lobed liver, which is supplied with a gallbladder. The pancreas is usually weakly isolated: its small lobules (islands) are adjacent to the stomach or interspersed in the liver. It produces insulin, and it is possible to use it as a raw material for obtaining this valuable therapeutic drug. The heart is located in front of the body cavity - in the area corresponding to the throat of the fish. It consists of an atrium and a ventricle, and only venous blood passes through it, pumped by the heart into the gills. From there, after being enriched with oxygen in the gill filaments, the blood enters the various organs of the body. Fish have a two-chambered heart and only one circulation. Only in lungfish, due to the presence of lungs, the circulatory system is more complicated. The kidneys of fish have the appearance of dark red ribbons, located immediately under the spine and extending along the entire dorsal edge of the body cavity. Between them and the intestines there is a swim bladder, which in fish carries the functions of a hydrostatic apparatus, as well as an organ that regulates gas exchange and, in some fish, the function of a sound resonator. The saccular ovaries (or ovaries) in females and the lobed whitish testes (or milks) in males have excretory canals that open outwards on the urogenital or special genital papilla, behind the anus. The brain in fish is usually very small and very primitive: the forebrain cortex, which serves as an associative center in higher vertebrates, is completely undeveloped in bony fish, in contrast to sharks, in which it consists of brain tissue. The centers of various senses are isolated in different parts of the brain: smell - in the forebrain, vision - in the middle, hearing and touch - in the medulla oblongata, the center of coordination of movements - in the cerebellum. The relative size of these divisions corresponds to the role of the various senses of the fish, and appearance brain allows you to judge the way of life. Special meaning has a lower cerebral appendage - the pituitary gland, which looks like a small onion sitting on the lower surface of the brain, behind the intersection of the optic nerves. Injection of pituitary extract into maturing female fish extremely accelerates the maturation of eggs and is used for this purpose in industrial fish farming.

Topic: Characteristics of amphibians

Amphibians, or amphibians, are the first, relatively small group of primitive terrestrial vertebrates. However, they still retain a close relationship with the aquatic environment. This is most fully manifested during the period of embryonic and postembryonic development. The laying of caviar (eggs) and its development in the vast majority of amphibians occurs in water.

The larvae that emerged from the eggs - tadpoles also live in the aquatic environment. They have the characteristics of typical aquatic animals: gill breathing, a two-chambered heart, one circle of blood circulation, and lateral line organs. After metamorphosis, amphibians acquire the characteristics of typical terrestrial vertebrates.

Adult amphibians are characterized by pulmonary respiration. Accordingly, the circulatory system changes: the heart becomes three-chambered, the pulmonary circulation occurs, the branchial arteries are replaced by carotid arteries homologous to them, systemic arches and aorta, and pulmonary arteries. The posterior vena cava, characteristic of terrestrial vertebrates, appears. The sense organs are noticeably improved: the shape of the cornea of ​​the eye becomes convex, the lens becomes lenticular, movable eyelids and a middle ear cavity with a tympanic membrane and an auditory bone - a stirrup - appear. The digestive tract is much more differentiated than that of fish. Terrestrial limbs of the five-fingered type appear. The limb belts become more complex. A strong articulation of the hind limb belt with the axial skeleton is carried out, etc.

However, despite these transformations, amphibians are still poorly adapted to living on land. This is expressed in the weak development of the lungs, and therefore bare skin plays an important role in the breathing process. Easily permeable to gases and water, the skin does not protect the body from drying out, which necessitates constant replenishment of water losses. A three-chambered heart does not provide complete separation of blood, and mixed blood is carried more or less throughout the body. The limbs are still poorly developed and cannot hold the body in an elevated position above the ground. The genitourinary system in almost all amphibians does not fundamentally differ from that in fish. Amphibians, like fish, are characterized by poikilothermy (inconstancy of body temperature).

The skeleton of a typical representative of the amphibian class - frogs - is characterized by a combination of progressive features characteristic of terrestrial vertebrates, with a number of adaptive features.

The first can be named: free limbs of the five-fingered type, the formation of belts and limbs from three homodynamic elements (built according to a single scheme), the connection of the pelvic girdle with the axial skeleton, autostyle, i.e., the fusion of the palatine-square cartilage with the skull, the transformation of the hyoid arch , reduction of the gill covers and part of the gill arches, great differentiation of the spine.

Features of specialization in the frog skeleton are manifested in slight ossification of the skull, poor development of the cervical and sacral spine, absence of ribs, replacement of the caudal vertebrae with one bone - the urostyle, elongation of the iliac bones, and in significant deviations of the skeleton of the free limbs from the typical five-fingered limbs of terrestrial vertebrates. However, in other groups of amphibians (tailed and legless) not all of the listed adaptive traits are found.

Theme: Characteristics of reptiles

Reptiles are the first class of higher land vertebrates. They differ from amphibians in a number of progressive features and adaptation to a terrestrial lifestyle. The structure of the central nervous system, the brain and sensory organs, is more complex than that of amphibians and deserves special attention.

In the brain of reptiles, the hemispheres of the forebrain are much more developed. The gray medulla forms the surface layer, the real cerebral cortex - the secondary cerebral fornix.

Among the progressive features of reptiles, the development of the skeleton as a whole should be noted. The appearance of a real ribcage provides a stronger support for the forelimbs. Strengthening the pelvic girdle by attaching it to the transverse processes of two (and not one, as in amphibians) sacral vertebrae contributes to increased support on the hind limbs.

In reptiles, the heel joint is not located between the lower leg and foot, as in amphibians, but between two rows of tarsal bones. Thus, the so-called intertarsal (intertarsal) articulation is formed, which is very characteristic of many reptiles and all birds.

The massive bony skull articulates with the spine with one condyle. The isolation of the neck, as well as the formation of the first two cervical vertebrae, which are special in structure - the atlas and the epistrophy - provide greater head mobility.

Breathing in reptiles is exclusively pulmonary. Well spilled trachea is divided into two bronchi included in the lungs. The lungs have a more complex structure than those of amphibians; they are characterized by internal complex partitions that reduce the overall cavity of the lung. The degree of development of these partitions in different groups of reptiles is not the same. In lizards and snakes, they are poorly developed, in turtles and crocodiles, the lungs are already massive spongy organs.

The circulatory system of reptiles is also more perfect than that of amphibians. Most reptiles have a three-chambered heart and, in addition, an incomplete septum develops in the ventricle (crocodiles have a four-chambered heart). The arterial trunk breaks up into three vessels, which depart independently from various parts of the ventricle.

An essential aspect of the higher organization of reptiles is the development of the pelvic buds (metanephros).

The most important adaptive features reptiles to life on land are exclusively internal fertilization, an increase in the size of eggs and the appearance of embryonic membranes.

A large egg, usually covered with dense shells, with a significant supply of yolk, ensures the development of the embryo out of water and without larval stages. In the process of development of the embryo, a system of embryonic membranes appears, of which the amniotic membrane, or amnion, served as the basis for uniting higher vertebrates into the amniote group.

The skin of reptiles has an important adaptive value. Horn formations are formed in it - scales, shields that make up the outer cover that protects the body from drying out. There are almost no glands in the skin of reptiles.

characteristic feature reptiles is a periodic molt, during which the old stratum corneum of the skin is replaced by a new one.

The skeleton of reptiles is more perfect in comparison with the skeleton of amphibians and is characterized by the progressive development of bone elements, the strengthening of the limbs and the strength of their attachment to the axial skeleton, which is associated with life on land.

An important feature of the lizard's skull is its almost complete ossification; insignificant remnants of cartilage are observed only in the olfactory and auditory regions. Especially a large number of integumentary ossification forms the roof, sides and bottom of the skull. The skull is articulated with the spine by one condyle formed by the occipital bones.

A characteristic feature of the skull of reptiles is the presence of peculiar pits in the temporal region. The temporal fossae and the bone lintels limiting them - the temporal arches - were formed as a result of a long evolution of the outer roof of the skull of ancient reptiles.

The skull, while maintaining its strength, became lighter. This feature also contributes to the strengthening of the muscles that compress the jaws, which have become more massive and, when contracted, enter the temporal pits.

The visceral skeleton is greatly altered. The teeth sit on the maxillary, premaxillary, pterygoid, and mandibular bones. Unlike amphibians, there are no teeth on the vomer.

The spine is divided into four sections. In a lizard, like in all reptiles, the spine is composed of a significant number of vertebrae. Biconcave (amphicoelous) vertebrae are extremely rare among reptiles; in most forms, the vertebrae are anteriorly concave (procoelous).

A characteristic feature of reptiles is the appearance of the chest (absent in snakes and turtles), the formation of which is associated with the presence of ribs and sternum. The ribs articulate with the transverse processes of the vertebrae. The true ribs also articulate with the sternum; there are also freely ending false ribs.

The limb belts of reptiles are quite strong formations. In the lizard, a lot of cartilage is still preserved in the girdle of the forelimbs, but the girdle is firmly connected to the chest, and the support on the forelimbs is well expressed here. The skeleton of the forelimb is of a typical terrestrial type, but still poorly developed.

The pelvic girdle is well developed, composed of three massive bones, at the place of their articulation an acetabulum is formed, into which the femoral head enters. Both halves of the belt are interconnected by means of a cartilaginous layer.

Unlike amphibians, a double pubic-sciatic articulation appears between both halves of the pelvis, which helps to strengthen the pelvis. The ilium of each side is attached to the transverse processes of the two sacral vertebrae behind the acetabulum.

The skeleton of the hind limb retains the usual structure for terrestrial vertebrates.

Topic: Characteristics of birds

Birds are a progressive branch of reptiles, (adapted to flight.

The most important features that distinguish birds from reptiles include:

1. Further development of the nervous system, the complexity of the highest nervous activity and the perfection of the senses, especially sight and hearing.

2.High and constant body temperature.

3. A perfect way to move through the air by flying, which does not entail the loss of the ability to move on the ground or climb.

4. Reproduction is accompanied by such complex biological phenomena as nest building, incubation of eggs, feeding and protection of chicks, which provide increased survival of offspring.

The noted features allowed birds to spread widely throughout the globe.

Among vertebrates, constant body temperature, or homeothermia, first arose in birds. This happened due to the complete separation of arterial and venous blood flows (four-chamber heart and one aortic arch) and intensive oxygen supply to tissues. The latter increases the metabolic rate and causes the appearance of a constant body temperature.

Maintaining a constant body temperature is also provided by the large size of the heart, which increases the speed of blood flow; the presence of a heat-insulating feather cover that protects the body from cooling; extremely energetic breathing processes, providing an abundant supply of oxygen to the blood and excretion carbon dioxide; the presence of air sacs that increase the intensity of breathing and prevent overheating of the body during the flight; rapid assimilation of food, contributing to an energetic metabolism.

When analyzing the structure of birds, it is important to note, firstly, the features that show their relationship with reptiles, and, secondly, the features associated with flight.

The first signs include:

1) thin skin, poor in glands;

2) strong development of horn formations;

3) one occipital condyle;

4) intertarsal joint;

5) the presence of a cloaca, etc.

The second ones include:

1) the transformation of the forelimbs into wings;

2) a feather cover that increases the bearing surface of the body and gives it a streamlined shape;

3) a decrease in body density due to the pneumaticity of the bones and the replacement of heavy jaws with a light, horny, toothless beak;

4) the keel of the sternum as a place of attachment of highly developed pectoral muscles moving wings;

5) air sacs that perform a variety of functions, especially important for breathing during flight;

6) a number of features of the skeleton.

In addition, flight is often associated with dense fixation of the lungs in the body cavity, the absence of a bladder, and asymmetry in the female reproductive system (almost all birds lack the right ovary and right oviduct).

The skeleton of birds is durable and light, which is a consequence of adaptation to flight. Strength is achieved both by a high content of mineral salts in the bones, and by the complete fusion of individual bones. Lightness is due to the pneumaticity of many bones, resulting from the reduction of the bone marrow. The air cavities of the bones are connected to the cavity of the air sacs. However, the relative mass of the skeleton (relative to body weight) in birds is approximately the same as in mammals (8-18% and 6-14%, respectively), although the latter have thicker bones and no air cavities in them. This is explained by the fact that in birds the relative length of the skeletal elements of the limbs and some other parts of the body is noticeably greater.

The forelimbs are turned into wings. The bones of the hand are underdeveloped and lightened, representing a support for long flight feathers. In connection with the transfer of the function of walking and grasping only to the hind limbs, a complex sacrum develops in the process of evolution as a reliable support for them.

The spine is completely differentiated into 5 sections: cervical, thoracic, lumbar, sacral and caudal. The cervical region is mobile, the vertebrae of the remaining departments grow together, forming a strong support for the body.

The sternum is strongly developed and carries a high crest, or keel, to which large muscles are attached that move the wings. The keel is absent only in flightless birds, for example, in ostriches, however, it is preserved in penguins, whose wings function when diving.

The low mobility of the spine, the presence of a large sternum and funnel-shaped processes on the ribs give the chest and the entire body a special strength, which is of great importance during flight.

Topic: Characteristics of mammals

The perfection of organization allowed mammals to spread widely around the globe. At present, they are absent only in the central part of Antarctica.

According to the nature of connections with the environment, several groups of mammals are distinguished: terrestrial, underground, arboreal, flying (air) and aquatic animals. In addition, there are transitional groupings that clearly demonstrate the ways of adaptive evolution of this class of vertebrates.

In addition to live birth and feeding offspring with milk, mammals are characterized by a number of features; some of them are also found in other groups of vertebrates, some are not characteristic of all species of mammals, and only some of these characters are unique. Among these features:

The presence of hair (wool), sweat and sebaceous glands

A special type of brain structure (including the strong development of the telencephalon, the transition to it of the functions of the main visual center and the control center for complex forms of behavior)

The presence of three auditory ossicles of the middle ear, external ear canal and auricle

Seven vertebrae in the cervical spine

warm-bloodedness

· Four-chambered heart. One (left) aortic arch

The alveolar structure of the lungs

Teeth sitting in the cells (alveoli) of the jaws; heterodont (different teeth)

Non-nuclear erythrocytes

In mammals, the spine is divided into five sections: cervical, thoracic, lumbar, sacral, and caudal. Only cetaceans do not have a sacrum. The cervical region almost always consists of seven vertebrae. Thoracic - from 10-24, lumbar from 2-9, sacral from 1-9 vertebrae. Only in the caudal region, their number varies greatly: from 4 (in some monkeys and humans) to 46.

Real ribs articulate only with the thoracic vertebrae (rudimentary may be on other vertebrae). In front, they are connected by the sternum, forming the chest. The shoulder girdle consists of two shoulder blades and two collarbones. Some mammals do not have clavicles (ungulates), in others they are poorly developed or replaced by ligaments (rodents, some carnivores).

The pelvis consists of 3 pairs of bones: iliac, pubic and ischial, which are tightly fused together. Cetaceans do not have a true pelvis.

The forelimbs serve as mammals for movement on the ground, swimming, flight, grasping. The humerus is greatly shortened. The ulna is less developed than the radius and serves to articulate the hand with the shoulder. The hand of the forelimb consists of the wrist, metacarpus and fingers. The wrist consists of 7 bones arranged in two rows. The number of metacarpus bones corresponds to the number of fingers (no more than five). The thumb consists of two joints, the rest - of three. In cetaceans, the number of joints is increased.

The respiratory system of mammals consists of the larynx and lungs. The lungs are distinguished by a large branching of the bronchi. The thinnest of them are the bronchioles. At the ends of the bronchioles are thin-walled vesicles (alveoli), densely braided with capillaries. The diaphragm is a characteristic anatomical feature of mammals. Plays an important role in the process of respiration.

Mammals have a four-chambered heart. It consists of the right and left ventricles, as well as the right and left atria. The chambers of the heart communicate with each other and with the main vessels with the help of valves. The heart provides oxygen and nutrients to the tissues of the body, freeing them from decay products. Arteries have elastic walls, veins are equipped with valves inside. Mammals have one (left) aortic arch.

The kidneys in mammals are bean-shaped and located in the lumbar region, on the sides of the spine. In the kidneys, as a result of blood filtration, urine is formed, then it flows down the ureters into the bladder. Urine comes out of it through the urethra.

In mammals, the forebrain and cerebellum are especially developed. The cerebral cortex is formed by several layers of nerve cell bodies and covers the entire forebrain. It forms folds and folds with deep furrows in most mammalian species. The more folds and convolutions, the more complex and diverse the behavior of the animal. Also, mammals have a well-developed peripheral nervous system, which provides them with the highest speed of reflexes. The sense organs include: 1. The organs of vision 2. The organs of hearing 3. The organs of smell 1. The organs of vision have great importance in the life of mammals. Unlike birds, each eye of which sees objects separately, mammals have binocular vision. 2 In the organs of hearing there is an external auditory canal and an auricle. 3 The olfactory organs are located in the anterior and posterior sections of the nasal cavity.

The digestive system of mammals is a gastrointestinal tract - a tube connecting the mouth to the anus. The digestive system includes: oral cavity, salivary glands, pharynx, esophagus, stomach, intestines, anus.

Most mammals have teeth (except monotremes, some cetaceans, pangolins and anteaters). They are found in the cells of the jaw bones. There are four types of teeth: incisors, canines, false-rooted and true molars.

After entering the oral cavity, the food is chewed by the teeth. Then the food is moistened with saliva, which flows through the ducts from the salivary glands. This makes it easier to swallow and move down the esophagus. Under the influence of saliva complex carbohydrates(starch, sugar) contained in food are converted into less complex. The salivary glands are highly developed in herbivores. A cow, for example, secretes 60 liters of saliva per day. In most animals, saliva has pronounced antiseptic properties.

The esophagus ensures that the food bolus enters the stomach.

Most mammals have a single chamber stomach. In its walls are glands that secrete digestive juice. But herbivorous mammals, such as deer, cow, goat, sheep, etc., have a multi-chambered stomach.

The intestine is divided into thin and large. The small intestine includes the duodenum, jejunum, and ileum. To the thick - the cecum, colon and rectum.

In the small intestine, food is digested under the influence of digestive juices. They are secreted by the glands of the intestinal walls, as well as by the liver and pancreas, which open into the initial section of the small intestine - the duodenum. Nutrients in the small intestine are absorbed into the blood, and the remains of undigested food enter the large intestine.

At the junction of the small and large intestines, there is an ileocecal valve that prevents the forming feces from being thrown back into the small intestine. In the caecum, under the influence of bacteria, there is a change in indigestible food substances. Also, in most mammals, there is a large amount of lymphatic tissue in the walls of the caecum, which makes it an important organ of the immune system. In many animals (for example, rabbits, beavers), the caecum is large. In some animals, it happens with an appendix. In the colon, the feces are dehydrated, accumulate in the rectum, and then are expelled out through the anus.

Topic: Animals listed in the "Red Book of Kazakhstan"

The vastness of the territory of Kazakhstan and the uniqueness of its geographical position in the very center of Eurasia have led to a great diversity natural conditions and, accordingly, the vegetation cover and the animal world. According to the Book of the Genetic Fund of the Fauna of Kazakhstan, there are 835 species of vertebrates alone - fish, amphibians, reptiles and mammals.

It includes 125 species and subspecies, 40 - mammals, or animals, 56 - birds, 10 - reptiles, 16 species of fish, amphibians - 3.

Subject to special protection

Ungulates - goitered gazelle, Turkmen kulan, argali; Ustyurt, Altai, Karatau mouflons; tugai deer;

Predatory - snow leopard, Tien Shan brown bear, dune cat, caracal, manul, honey badger;

rodents - beaver, Menzbier's marmot, selevinia, five-fingered and three-fingered pygmy jerboas;

Insectivores - muskrat, long-spined hedgehog;

waterfowl - curly and pink pelicans, whooper swan, flamingos, white and black storks;

Inhabitants of steppes and deserts - bustard, jack, gyrfalcon, demoiselle crane; predator birds- bearded vulture, kumai, golden eagle, imperial eagle, white-tailed eagle, falcons - peregrine falcon and saker falcon;

Reptiles - monitor lizard, yellow-bellied lizard, motley roundhead, ocellated foot and mouth disease, 4 species of snakes, amphibians - Semirechensky newt;

fish - Aral and Caspian salmon, Syrdarya pseudoshovelnose and lysach (pike asp).