General characteristics of the chordate type

Type Chordates

Inferior chordates. Subtype Cranial

TYPE CHORDS. LOWER CHORDS

General characteristics of the chordate type

Type Chordates combines animals diverse in appearance and lifestyle. Chordates are distributed throughout the world, have mastered a variety of habitats. However, all representatives of the type have the following common organizational features:

1. Bilaterally symmetrical chordates, deuterostomes, multicellular animals.

2. Chordates have a notochord throughout their life or at one of the phases of development. Chord- This is an elastic rod located on the dorsal side of the body and performing a supporting function.

3. Above the chord is located nervous system in the form of a hollow tube. In higher chordates, the neural tube is differentiated into the spinal cord and brain.

4. Under the chord is located digestive tube. The alimentary canal begins mouth and ends anus, or the digestive system opens into the cloaca. Throat pierced gill slits, which in primary aquatic organisms persist throughout their lives, while in terrestrial ones they are laid only at the early stages of embryonic development.

5. Beneath the digestive system lies heart. The circulatory system in chordates closed.

6. Chordates have secondary body cavity.

7. Chordates are segmented animals. Location of organs metameric, i.e. the main organ systems are located in each segment. In higher chordates, metamerism is manifested in the structure of the spinal column, in the muscles of the abdominal wall of the body.

8. The organs of excretion in chordates are varied.

9. Chordates have separate sexes. Fertilization and development are varied.

10. Chordates descended through a series of intermediate forms unknown to biology from the very first coelomic animals.

The chordate type is divided into three subtypes:

1. Subtype Cranial. These are 30-35 species of small marine chordates, resembling fish in shape, but without limbs. The notochord in the Skullless persists throughout life. Nervous system in the form of a hollow tube. The pharynx has gill slits for breathing. Representatives - Lancelets.

2. Subtype Larval-chordaceae, or Shellers. These are 1500 species of marine sedentary sedentary animals living in tropical and subtropical regions. Their body is in the form of a bag (the body size of one individual in a colony is no more than 1 mm, and single ones can reach 60 cm), there are two siphons on the body - oral and cloacal. Larval chordates are water filterers. The body is covered with a thick shell - a tunic (hence the name of the subtype - Tunics). As adults, the tunicates lack the notochord and neural tube. However, the larva, which actively swims and serves for settling, has a structure typical of Chordates and is similar to the Lancelet (hence the second name - Larval Chordates). Representative - Ascidia.

3. Subtype Vertebrates, or cranial. These are the most highly organized chordates. Nutrition in vertebrates is active: food is searched for and pursued.

The notochord is replaced by the vertebral column. The neural tube is differentiated into the spinal cord and brain. The skull is developed, which protects the brain. The skull bears jaws with teeth for grasping and grinding food. Paired limbs and their belts appear. Cranials have a much higher level of metabolism, a complex population organization, diverse behavior, and a pronounced individuality of individuals.

The subtypes Cranial and Larval Chordates are called the lower Chordates, and the Vertebrate subtype is the higher Chordates.

Subtype Cranial - Acrania

Lancelet

The subtype Cranial includes the only class of the Head Chordidae, which has only about 30-35 species of marine animals living in shallow water. A typical representative is Lancelet - Branchiostoma lanceolatum(Lancelet genus, class Headochord, subtype Cranial, type Chordata), the size of which reaches 8 cm. The body of the Lancelet is oval in shape, narrowed towards the tail, laterally compressed. Outwardly, the Lancelet resembles a small fish. Located on the back of the body tail fin in the form of a lancet - an ancient surgical instrument (hence the name Lancelet). Paired fins are absent. There is a small dorsal. On the sides of the body from the ventral side hang two metapleural folds, which fuse on the ventral side and form peribranchial, or an atrial cavity that communicates with the pharyngeal fissures and opens at the posterior end of the body with a hole - atriopore- outside. At the anterior end of the body near the mouth are the perioral tentacles, with which the Lancelet captures food. Lancelets live on sandy soils in the sea at a depth of 50-100 cm in temperate and warm waters. They feed on bottom sediments, marine ciliates and rhizopods, eggs and larvae of small marine crustaceans, diatoms, burrowing into the sand and exposing the front end of the body. More active at dusk, avoid bright lighting. Disturbed Lancelets swim quite quickly from place to place.

Covers. The body of the lancelet is covered skin, consisting of a single layer epidermis and thin layer dermis.

Musculoskeletal system. A chord stretches along the entire body. Chord- this is an elastic rod located on the dorsal side of the body and performing a supporting function. To the anterior and posterior ends of the body, the chord becomes thinner. The notochord protrudes into the anterior part of the body a little further than the neural tube, hence the name of the class - Cephalic. The notochord is surrounded by connective tissue, which simultaneously forms supporting elements for the dorsal fin and divides the muscle layers into segments using connective tissue

Type Chordates subtype Cranial Lancelet

layers. Individual muscle segments are called myomers, and the partitions between them myoseptami. Muscles are formed by striated muscles.

body cavity at the lancelet secondary in other words, they are coelomic animals.

Digestive system. On the front of the body is mouth opening, surrounded by tentacles(up to 20 pairs). The mouth opening leads to a large throat, which functions as a filtering apparatus. Through the cracks in the pharynx, water enters the atrial cavity, and food particles are directed to the bottom of the pharynx, where endostyle- a groove with a ciliated epithelium that drives food particles into the intestine. no stomach, but hepatic outgrowth, homologous to the liver of vertebrates. midgut, without making loops, opens anus at the base of the tail fin. Digestion of food occurs in the intestines and in the hollow hepatic outgrowth, which is directed towards the head end of the body. Interestingly, the Lancelet retained intracellular digestion, intestinal cells capture food particles and digest them in their digestive vacuoles. This mode of digestion is not found in vertebrates.

Respiratory system. There are more than 100 pairs in the throat of the Lancelet gill slits leading to peribranchial cavity. The walls of the gill slits are penetrated by a dense network of blood vessels in which gas exchange occurs. With the help of the ciliary epithelium of the pharynx, water is pumped through the gill slits into the peribranchial cavity and through the opening (atriopore) is brought out. In addition, gas-permeable skin also takes part in gas exchange.

Circulatory system. The circulatory system of the Lancelet closed. The blood is colorless and contains no respiratory pigments. The transport of gases is carried out as a result of their dissolution in the blood plasma. In the circulatory system one circle circulation. The heart is absent, and blood is moved by the pulsation of the gill arteries, which pump blood through the vessels in the gill slits. Arterial blood enters dorsal aorta, from which carotid arteries blood flows to the front, and through the unpaired dorsal aorta to the back of the body. Then by veins blood returns to venous sinus and by abdominal aorta heading for the gills. All blood from the digestive system enters the hepatic outgrowth, then into the venous sinus. The liver outgrowth, like the liver, neutralizes toxic substances that have entered the bloodstream from the intestines, and, in addition, performs other functions of the liver.

Such a structure of the circulatory system does not fundamentally differ from the circulatory system of vertebrates and can be considered as its prototype.

excretory system. The excretory organs of the lancelet are called nephridia and resemble the excretory organs of flatworms - protonephridia. Numerous nephridia (about a hundred pairs, one for two gill slits), located in the pharynx, are tubules that open with one hole into the coelom cavity, the other - into the paragillary cavity. On the walls of the nephridium are club-shaped cells - solenocytes, each of which has a narrow channel with a ciliated hair. Due to the beating of these

Type Chordates subtype Cranial Lancelet

hairs, the liquid with metabolic products is removed from the cavity of the nephridium into the peribranchial cavity, and from there it is already out.

central nervous system formed neural tube with a cavity inside. The lancelet does not have a pronounced brain. In the walls of the neural tube, along its axis, there are light-sensitive organs - eyes Hesse. Each of them consists of two cells - photosensitive and pigmented, they are able to perceive the intensity of light. An organ adjacent to the expanded anterior part of the neural tube smell.

Reproduction and development. The lancelets that live in our Black Sea and the lancelets that live in the waters of the Atlantic off the coast of Europe break into breeding in the spring and spawn eggs until August. Warm water lancelets breed all year round. lancelets separate sexes, sex glands (gonads, up to 26 pairs) are located in the body cavity in the pharynx. Sexual products are excreted into the peribranchial cavity through the temporarily formed genital ducts. Fertilization external in water. emerges from the zygote larva. The larva is small: 3-5 mm. The larva actively moves with the help of cilia that cover the entire body, and due to the lateral bends of the body. The larva swims in the water column for about three months, then passes to life at the bottom. Lancelets live up to 4 years. Sexual maturity is reached by two years.

Significance in nature and for man. The non-cranial are an element of biological diversity on Earth. They feed on fish and crustaceans. The Skullless themselves process dead organic matter, being decomposers in the structure of marine ecosystems. The non-cranial are essentially a living blueprint for the structure of chordate animals. However, they are not direct ancestors of vertebrates. In the countries of Southeast Asia, local residents collect Lancelets by sifting sand through a special sieve and eat them.

Non-cranial animals have retained a number of features characteristic of their invertebrate ancestors:

§ excretory system of nephridial type;

§ the absence of differentiated sections in the digestive system and the preservation of intracellular digestion;

§ filtering method of nutrition with the formation of a near-gill cavity to protect the gill slits from clogging;

§ metamerism (repetitive arrangement) of the genital organs and nephridia;

§ absence of a heart in the circulatory system;

§ weak development of the epidermis, it is single-layer, like in invertebrates.

Type Chordates subtype Cranial Lancelet

Rice. The structure of the lancelet.

A - neural tube, chord and digestive system; B - circulatory system.

1 - chord; 2. - neural tube; 3 - oral cavity; 4 - gill slits in the pharynx; 5 - peribranchial cavity (atrial cavity); 6 - atriopore; 7 - hepatic outgrowth; 8 - gut; 9 - anus; 10 - subintestinal vein; 11 - capillaries of the portal system of the hepatic outgrowth; 12 - abdominal aorta; 13 - pulsating bulbs of the arteries pumping blood through the gill slits; 14 - dorsal aorta.

Rice. Nephridium Lancelet.

1 - hole as a whole (into the secondary cavity of the body); 2 - solenocytes; 3 - opening into the circumbranchial cavity.

Type Chordates subtype Cranial Lancelet

Rice. Cross section of the Lancelet:

A - in the region of the pharynx, B - in the region of the midgut.

1 - neural tube; 2 - muscles; 3 - roots of the dorsal aorta; 4 - ovary; 5 - endostyle; 6 - abdominal aorta; 7 - metapleural folds; 8 - peribranchial (atrial) cavity; 9 - gill slits (due to the oblique position, more than one pair of them is visible on one transverse section); 10 - nephridia; 11 - whole; 12 - ventral (motor) spinal nerve; 13 - dorsal (mixed) nerve; 14 - chord; 15 - subintestinal vein; 16 - dorsal aorta; 17 - dorsal fin.

Questions for self-control.

Name the characteristic features of animals of the Chordata type.

Name the type classification into three subtypes.

Name the systematic position of the Lancelet.

Where does the lancelet live?

What is the body structure of the Lancelet?

1.General characteristics of the chordate type.Type Chordates combines animals that are very diverse in appearance, lifestyle and living conditions. Representatives of chordates are found in all the main environments of life: in water, on the land surface, in the thickness of the soil and, finally, in the air. They are geographically distributed throughout the world. The total number of species of modern chordates is approximately 40 thousand. The Chordata type includes non-cranial (lancelets), cyclostomes (lampreys and hagfish), fish, amphibians, reptiles, birds and mammals.

2. The main features of the type are chordates. 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. Let's consider the main features of the type using an interactive scheme: The body is two-sided - 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.

3. General taxonomy of the Chordata type. Of the four subtypes of chordates - hemichordata, larval-chordate Urochordata, non-cranial Acrania and vertebrate Vertebrata - we will focus on the last two, related to the progressive direction in the evolution of this type of animal. The subtype Cranial consists of only one class - Cephalochordata, which includes the lancelet; The subphylum Vertebrates includes the following classes: Cyclostomata Cyclostomata, Chondrichthyes Cartilaginous Fishes, Osteichthyes Bony Fishes, Amphibia Amphibians, Reptilia Reptiles, Aves Birds and Mammalia Mammals.

4. Origin of the Chordate type. Chordates are one of the largest types of the animal kingdom, whose representatives have mastered all habitats. This type includes three groups (subtypes) of organisms: tunicates (including marine sessile organisms living at the bottom - ascidians), non-cranial (similar to small fish sea creatures - lancelets), vertebrates (cartilaginous and bony fish, amphibians, reptiles, birds and mammals). Man is also a representative of the chordate type. The origin of the chordate type is the most important stage in the historical development of the animal world, which means the emergence of a group of animals with a unique structural plan, which made it possible in further evolution to achieve the maximum structural and behavioral complexity among living beings.

5.General characteristics of the subtype Shellers.hullers, or larval-chordates(lat. Tunicata, Urochordata listen)) is a subphylum of chordates. Includes 5 classes - ascidians, appendiculars, salps, fire-bearers and marrowers. According to another classification, the last 3 classes are considered units of the class Thalacea. More than 1000 species are known. They are found in seas around the world. The body is bag-shaped, surrounded by a shell or mantle ( Tunica) from tunicin, a material similar to cellulose. The type of food is filtering: they have two openings (siphons), one for the absorption of water and plankton (oral siphon), the other for its release (cloacal siphon). The circulatory system is not closed, a notable feature of the tunicates is a regular change in the direction in which the heart pumps blood.

6. Organization of Ascidians as typical representatives of tunicates. Ascidians are benthic animals leading an attached lifestyle. Many of them are single forms. Their body sizes are on average several centimeters in diameter and the same in height. However, some species are known among them that reach 40-50 cm, for example, the widespread Cione intestinalis or the deep-sea Ascopera gigantea. On the other hand, there are very small sea squirts, less than 1 mm in size. The alimentary canal of ascidians begins with a mouth located at the free end of the body on the introductory, or oral, siphon.

8. General characteristics of the subtype Cranial. Skullless- marine, mainly bottom animals that retain the main features of the Chordata type throughout their lives. Their organization represents, as it were, a diagram of the structure of a chordate animal: as an axial skeleton, they have chord, the central nervous system is represented neural tube, throat pierced gill slits. Available secondary mouth and secondary body cavity in general. In a number of organs, there is metamerism. Skullless animals are characterized bilateral (bilateral) symmetry body. These signs point to the phylogenetic relationship of the non-cranial with certain groups of invertebrates (annelids, echinoderms, etc.).

9.External and internal structures of the lancelet as a representative of the non-cranial subtype . lancelet (Amphioxus lanceolatus This small animal (6 - 8 cm long) lives in the shallow waters of the seas, burrowing into the bottom soil and exposing the front part of the body. The non-cranial, and in particular the lancelet, are characterized by a number of specific primitive features that distinguish them well from other representatives of the Chordata type. The skin of the lancelet is formed by a single layer of epithelium (epidermis) and is covered by a thin cuticle. The central nervous system is not differentiated into the brain 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 - eyes 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 are distinguished - pharynx and intestine. The blood of the lancelet is colorless, the heart is missing. The reproductive organs - the testes and ovaries - are similar in external structure and are rounded bodies.

11. General characteristics of the subtype Vertebrates. External features of the structure. The cranial subphylum includes all known vertebrates, whose likely evolutionary relationships are shown in. existence on land. Thus, reptiles are the first fully terrestrial vertebrates. Zoologists sometimes use the collective term amniotes for all wholly terrestrial vertebrates (reptiles, birds and mammals), in contrast to anamnia (amphibians and fish), in which the amniotic membrane is absent, and therefore they are necessarily forced to spend part of their life cycle or all of them in water. . The highest subtype of the chordate type, whose representatives have a bony or cartilaginous internal skeleton. It is divided into superclasses of fish and (jawless, cartilaginous fish and bony fish) and tetrapods (amphibians, reptiles, birds and mammals). The vertebrate subtype includes the following classes: fish, amphibians, reptiles, birds, and mammals.

13. Primitive, peculiar and specialized features of the class Cyclostomes. The only surviving representatives of the jawless - lampreys (Petromyzones) and hagfish (Myxini) - make up the class of cyclostomes (Cyclostomata), the most ancient of modern vertebrates. In contrast to the representatives of all higher classes, they do not have real jaws and their mouth does not open directly outward, but is placed in the depths of a kind of suction funnel, which is supported by a special ring-shaped cartilage. Their skin is bare and slimy. True teeth are absent; instead, the oral funnel is armed with horny teeth. Paired limbs cyclostomes are deprived. The nasal opening is one, unpaired, since the organs of smell are combined into one nasohypophyseal sac. The visceral skeleton looks like an openwork lattice and is not divided into separate segmented arches. Finally, the respiratory organs of cyclostomes are represented by 5-15 pairs of peculiar gill sacs of endoderm origin.

15. Systematics of the section Jawless. (up to representatives). Jawless(lat. Agnatha) - an archaic group (superclass or clade) of chordate cranials, almost completely extinct in our time, with the exception of 39 lamprey species and 76 hagfish species. Jawless are characterized by the absence of jaws, but they have a developed skull, which distinguishes them from non-cranial. Mixins and lampreys have traditionally been considered a monophyletic group and have been grouped together under the name cyclostomes (Cyclostomata). But there is also an alternative hypothesis, according to which minohyphylogenetically is closer to gnats than to hagfishes.

16. General characteristics of the class Cartilaginous fish in connection with an active lifestyle. CLASS CHONDRICHTHYES. Cartilaginous fish arose in the Upper Silurian from jawless fish, moving to faster, longer swimming and more successful capture of prey with armed jaws by the mouth. They were the first jawed vertebrates and dominated, gradually evolving, until the middle of the Mesozoic era, when they began to be replaced by higher bony fish. Currently, there is only one small group of carnivorous cartilaginous fish called elasmobranchs. They are widely distributed in the seas. The elasmobranchs include sharks - excellent swimmers - and rays, leading a sedentary lifestyle at the bottom. Sharks are about 350 species, stingrays are about 340 species. Most cartilaginous fish are large in size. The length of the largest sharks reaches 15-20 m, rays - 6-7 m. There are few small species.

17. Systematics of the class Cartilaginous fishes. class Cartilaginous fishes (lat. Chondrichthyes). It is one of two existing classes of fish. The class of cartilaginous fishes is divided into the subclass Elasmobranchii or laminobranchs and the subclass Holocephali or whole-headed fishes. The best-known members of this class are the Selachii or sharks and the Batoidea or rays. Both those and others belong to the subclass of laminobranchs.

20. Primitive Featuresstructures of organ systems of cartilaginous fishes. All cartilaginous fish are characterized by the following primitive features: the skin is either covered with placoid scales or naked (in chimeras and some rays), gill slits open outward, like lampreys, and only chimeras have skin membranes that cover the gill slits. The skeleton has no bones and is formed exclusively by cartilage (which, however, is often saturated with lime), unpaired fins and the distal part of paired fins are supported by elastin ("horny") rays, there are wide interbranch septa, usually reaching the surface of the body, there is not a swim bladder, no lungs.

18. The external structure of the shark as the first jawed vertebrates. sharks(lat. Selachii) - above the detachment of cartilaginous fish (Chondrichthyes), belonging to the subclass of gill plates (Elasmobranchii) and having the following distinctive features: an elongated body of a more or less torpedo-shaped shape, a large heterocercal caudal fin, usually a large number of sharp teeth on each jaw. The word "shark" comes from the Old Norse "hákall". The most ancient representatives already existed about 420-450 million years ago. To date, more than 450 species of sharks are known: from the deep-sea shallow Etmopterus perryi, only 17 centimeters long, to the whale shark (Rhincodon typus) - the largest fish (its length reaches 20 meters). Representatives of the above detachment are widespread in the seas and oceans, from the surface to a depth of more than 2000 meters. They mainly live in sea water, but some species are also able to live in fresh water. Most sharks are so-called real predators, but 3 species - whale, giant and large-mouthed sharks - filter feeders, they feed on plankton, squid and small fish.

19. Progressive features of the structure of the organ systems of cartilaginous fish. These most primitive fish include sharks, rays and peculiar chimeras that inhabit the seas and oceans everywhere. Some live in fresh water. Along with very ancient features of organization, modern cartilaginous fish have a highly developed nervous system and sensory organs and a very perfect biology of reproduction. brain, males have peculiar copulatory organs, representing modified parts of the ventral fins, insemination is internal, and females either lay large eggs covered with a dense horn-like membrane, or give birth to live cubs, the development of which occurs in the "womb".

21. Systematics of the class Bony fish. Bone fish(lat. Osteichthyes) is a group of classes in the superclass Pisces ( Pisces). Bony fish have paired limbs (fins). The mouth of these fish is formed by grasping jaws with teeth, the gills are located on the gill arches with an internal skeletal support, the nostrils are paired. From the oral cavity, food passes into the pharynx, from it into the esophagus, and then into the voluminous stomach or immediately into the intestines. Partial digestion of food occurs in the stomach under the influence of gastric juice. The final digestion of food takes place in the small intestine. The duct of the gallbladder, liver and pancreatic duct flows into the initial section of the small intestine. In the small intestine, nutrients are absorbed into the blood, and undigested food remains are removed through the anus. Gill breathing. From the oral cavity, water passes through the gill slits, washes the gills and exits from under the gill covers. Gills are made up of gill arches, which in turn are made up of gill filaments and gill rakers. The circulatory system of fish is closed, the heart consists of 2 chambers: the atrium and the ventricle. From the ventricle to the gills, a large blood vessel departs - aorta, branching into smaller ones - arteries. In the gills, the arteries form a dense network of tiny vessels - capillaries. Substances that are unnecessary for the body are excreted from the blood when they pass through the excretory organs - the kidneys. Two ureters depart from the kidneys, through which urine flows into the bladder, and is removed outward through the opening behind the anal. In most species, fertilization is external. In species with internal fertilization, the copulatory organ of males is formed by a modified part of the anal fin.

22. Features of the progressive organization of the class Bony fish. In bony fish, the cartilage in the skeleton is to some extent replaced by bone tissue: the main or replacement bones are formed. In addition, integumentary bones appear in the skin, which then sink under the skin and are part of the internal skeleton. The skeleton of bony fish is subdivided into the axial skeleton, the skull (cerebral and visceral), the skeleton of unpaired fins, the skeleton of paired fins and their belts.

24. Features of the structure of organ systems of bony fish, as progressive aquatic vertebrates. They have scales of the ganoid, cycloid or ctenoid type. The skeleton is bony. In the internal cavity of bony fish are the organs of digestion, blood circulation, excretion and reproduction. The complex of progressive features of the structure of bony fishes is especially clearly and fully expressed in the youngest and most progressive branch of this class, Teleostei teleosts, which includes the vast majority of living forms of this class.

26.Subclass Ray-finned as the main group of the class bony fish, its characteristics. ray-finned fish(lat. Actinopterygii listen)) is a class of fish from the superclass bony fish. The vast majority of known modern fish species (over 20,000 or about 95%) are ray-finned. Representatives of this particular subclass inhabit water bodies of all types: from many kilometers deep ocean and salt lakes to streams and underground sources. Fish scales are ganoid or bony. Some scales, merging, form bony plates, while others have bare skin. A well-developed notochord has been preserved only in a few species, usually fish have bony vertebrae. In ray-finned swim bladders, in a few species it is secondarily reduced.

27. General characteristics of the Amphibian class, as the first terrestrial vertebrates. Amphibians, or amphibians (lat. Amphibia) - a class of vertebrate tetrapods, including newts, salamanders, frogs and caecilians - more than 6700 in total (according to other sources - about 5000) modern species, which makes this class relatively few in number. In Russia - 28 species, in Madagascar - 247 species. The group of amphibians belongs to the most primitive terrestrial vertebrates, occupying an intermediate position between terrestrial and aquatic vertebrates: reproduction and development in most species occurs in the aquatic environment, while adults live on land. All amphibians have smooth thin skin, relatively easily permeable to liquids and gases. The structure of the skin is characteristic of vertebrates: a multilayered epidermis and the skin itself (corium) stand out. The skin is rich in skin glands that secrete mucus. In some, the mucus may be poisonous or facilitate gas exchange. The skin is an additional organ for gas exchange and is supplied with a dense network of capillaries. Horn formations are very rare, and ossification of the skin is also rare: Ephippiger aurantiacus and the horned toad of the species Ceratophrys dorsata have a bone plate in the skin of the back, legless amphibians have scales; in toads, sometimes, under old age, lime is deposited in the skin.

23. External structure of bony fish and its diversity. The movement of bony fish is carried out with the help of fins. The mouth is armed with movable jaws. New features of a higher organization in this class are manifested primarily in the ossification of their internal skeleton and in the appearance of various bone formations in the skin in many species. This makes the musculoskeletal system of the body stronger, protects the internal organs. Significant changes are noticeable in the structure of the gill apparatus: bony fish have developed gill covers that protect the respiratory organs.

29. Systematics of the Amphibian class. Amphibians are the smallest class of vertebrates, including only about 2100 modern species. Of all classes of vertebrates, amphibians occupy the most limited space on the globe, being associated with the coastal parts of only fresh water bodies, and are absent both in the sea and on oceanic islands. Modern amphibians are represented by three orders, very different in number of species. The most numerous are tailless amphibians (Ecaudata, or Anura), which have adapted to moving on land by jumping with the help of elongated hind limbs (hence their name jumping - Salientia) and distributed throughout all continents. More primitive are the tailed amphibians (Caudata, or Urodela), whose typical representatives are newts and salamanders, which are much rarer and distributed almost exclusively in the northern hemisphere (about 280 species). Finally, the third, smallest order of the legless (Apoda) contains only tropical worms, which are apparently the remains of very ancient armored amphibians that have survived to this day due to specialization in a burrowing lifestyle (about 55 species).

28. Features of the class Amphibians as animals leading a dual lifestyle. Most amphibians spend their lives in humid places, alternating between being on land and in water, but there are some purely aquatic species, as well as species that spend their lives exclusively on trees. Insufficient adaptability of amphibians to living in a terrestrial environment causes drastic changes in their lifestyle due to seasonal changes in living conditions. Amphibians are able to hibernate for a long time under adverse conditions (cold, drought, etc.). In some species, activity can change from nocturnal to diurnal as temperatures drop at night. Amphibians are active only in warm conditions. At a temperature of +7 - +8 ° C, most species fall into a stupor, and at -1 ° C they die. But some amphibians are able to endure prolonged freezing, drying out, and also regenerate significant lost parts of the body. Some amphibians, such as the sea toad Bufo marinus can live in salt water. However, most amphibians are found only in fresh water. Therefore, they are absent on most oceanic islands, where conditions are favorable for them in principle, but which they cannot reach on their own.

38. Systematics and features of the subclass Archosaurs. Archosaurs lat. Archosauria are reptiles that are very diverse in appearance, structure, size, lifestyle and habitat. Their common feature is the diapsid type of skull (two temporal windows) and the presence in it of additional eye holes (windows), thecodont teeth that do not have roots and form in separate cells (alveoli). The subclass of archosaurs is divided into four superorders: thecodonts, dinosaurs, pterosaurs and crocodiles. Archosaurs appeared in Perm and exist to this day. Thecodonts existed from the Late Permian to the Triassic, dinosaurs from the Middle Triassic to Cretaceous, pterosaurs from the Late Triassic to Cretaceous, and crocodiles from the Late Triassic to the present day.

31. General characteristics and taxonomy of the subclass Arcuvertebral amphibians. The first subclass of the arcuate (Apsidospondyli) contains 4 orders, bearing the common name of the superorder of labyrinthodonts (Labyrinthodontia). The most ancient detachment of Devonian stegocephalians - ichthyostegs (Ichtyostegalia) - preserved the remains of the gill cover of fish. The labyrinthodonts include the detachment of embolomeric stegocephals (Embolomeri), which was widespread in the Carboniferous period, the Permian rachitomous (Rachitomi), and the stereospondylic stegocephals (Stereospondyli4o), which separated from them in the Triassic. This whole group of labyrinthodonts disappeared at the border of the Jurassic period.

32. The external structure of the frog as a representative of the class of amphibians. The pond frog has a short and wide body, gradually turning into a flat head. The neck is not pronounced. The tail is missing. Above the large mouth are the nostrils, and above them are the bulging eyes. The nostrils have valves that close the access of water to the lungs when the animal is immersed in water. Behind each eye are the hearing organs, consisting of the inner ear and the middle ear (closed by the eardrum). The body rests on two pairs of dissected limbs. The hind limbs are the most developed. With their help, the frog moves by jumping on land and swims well. Between the fingers of the hind limbs there is a swimming membrane.

33. Features of the internal structure of a frog as a representative of the class of amphibians. The skeleton of amphibians consists of the same main sections as the skeleton of fish. It is based on the skull, spine, bones of free limbs and their belts. Unlike fish, the skull of a frog is movably articulated with the spine, and the ribs are not developed. The main distinguishing features in the structure of the skeleton are associated with the emergence of amphibians on land and with movement on a solid surface with the help of free limbs - front and hind legs. The bones of their belts serve as a support for the skeleton of the fore and hind limbs. In the skeleton of the forelimb, the humerus, bones of the forearm and hand are distinguished. In the skeleton of the hind limb - the femur, the bones of the lower leg and foot. The movable articulation of the bones in the limbs allows the frog to move not only in water, but also on land. The structure of the muscular system in a frog is also more complicated than that of a fish. In connection with movement on land, amphibians develop the muscles of free limbs, especially the hind limbs.

34. Features of the structure of amphibians that arose as adaptations for living on land. Frogs live almost throughout the entire territory of our country, except for the Far North of Siberia and high mountain regions. They live in damp places: in swamps, wet forests, meadows, along the banks of freshwater reservoirs or in water. On land, mostly adults are found, and reproduction, growth, and development of larvae occur in water. The behavior of frogs is largely determined by humidity. In dry weather, some species of frogs hide from the sun, but after sunset or in wet, rainy weather, it is time for them to hunt. Other species live in the water or near the water itself, so they hunt during the day. Frogs are active in the warm season. With the onset of autumn, they leave for the winter. For example, the common frog hibernates at the bottom of non-freezing reservoirs, in the upper reaches of rivers and streams, accumulating in tens and hundreds of individuals, they freeze along with the water, and with the onset of heat they begin an active lifestyle.

35 . Reptiles as the first class of true terrestrial vertebrates. Class REPTILES OR REPTILIA (Reptilia) Reptiles, compared with amphibians, represent the next stage in the adaptation of vertebrates to life on land. These are the first true terrestrial vertebrates, characterized by the fact that they reproduce on land with eggs, breathe only with the lungs, their breathing mechanism is of a suction type (by changing the volume of the chest), the conducting airways are well developed, the skin is covered with horny scales or scutes, the skin glands are almost no, in the ventricle of the heart there is an incomplete or complete septum, instead of a common arterial trunk, three independent vessels depart from the heart, the pelvic kidneys (metanephros). In reptiles, mobility increases, which is accompanied by a progressive development of the skeleton and muscles: the position of various parts of the limbs in relation to each other and to the body changes, the limb belts become stronger, the spine is divided into cervical, thoracic, lumbar, sacral and caudal sections, head mobility increases. The skull of reptiles, like that of birds, unlike other vertebrates, is connected to the spine by one (unpaired) condyle. In the skeleton of free limbs, intercarpal (intercarpal) and intertarsal (intertarsal) joints are characteristic. In the girdle of the forelimbs, they have a kind of integumentary bone, the sternum. Now there are about 7,000 species of reptiles, that is, almost three times more than modern amphibians. Reptiles living today are divided into 4 orders: Scaly; Turtles; Crocodiles; Beakheads.

36. General characteristics of the Reptile class. Features of the organization. Reptiles - the first class of real primary terrestrial vertebrates (Amniota). Relatively large, rich in yolk and protein eggs covered with a thick parchment-like shell. Fertilization only internal. Embryonic development goes in the air with the formation of germinal membranes - amnion and serosa - and allantois; the larval stage is absent. A young animal hatched from an egg differs from adults only dimensions.Dry leather reptiles are almost devoid of glands. The outer layers of the epidermis become keratinized; horny scales and scutes form in the skin. Breath only lung. Airways are formed - the trachea and bronchi. Breathing is carried out with movements of the chest. Heart three-chamber. Three blood trunks independently depart from the ventricle divided by an incomplete septum: two aortic arches and a pulmonary artery. The carotid arteries supplying the head arise only from the right aortic arch. The large and small circles of blood circulation are not completely separated, but the degree of their separation is higher than that of amphibians. Selection and water exchange is provided by metanephric (pelvic) kidneys. An increase in the relative size of the head brain, especially due to the increase in the hemispheres and cerebellum. Skeleton completely ossified. The axial skeleton is subdivided into five sections. Elongation of the neck and specialized first two cervical vertebrae (atlas and epistrophe) provide high head mobility. Scull has one occipital condyle and well developed integumentary bones; the formation of temporal pits and the bone temporal arches limiting them is characteristic. limbs ground type with intercarpal and intertarsal articulations. The girdle of the forelimbs is connected to the axial skeleton through the ribs, the pelvic girdle articulates with the transverse processes of the two sacral vertebrae. reptiles populate various ground habitat predominantly in warm, partly in temperate latitudes; some of the species reverted to water lifestyle.

30. General characteristics and taxonomy of the subclass Thin Vertebrates. The second subclass of amphibians - thin-vertebral, or lepospondyli (Lepospondyli) - combines several groups, mostly small stegocephalians (Microsauria), very numerous in the Carboniferous, but already extinct in the Permian period. Recently, lepospondylic stegocephalians are considered the ancestral group for two modern orders of amphibians: caudate (Caudata, or Urodela) and legless (Apoda). However, there is no direct connection between them, since the fossil remains of modern orders were found only in the Cretaceous period, and the lepospondylia died out already in the Permian.

37 . Systematics and features of the subclass Anapsida. Anapsids (lat. Anapsida) are amniotes, whose skull does not have temporal windows. Traditionally, anapsids were considered as a monophyletic taxon of reptiles, however, it was hypothesized that some groups of reptiles with anapsid skulls can only be distantly related to each other. Many modern paleontologists believe that turtles evolved from diapsid reptiles that lost the holes in their cheek bones, although this hypothesis is not shared by everyone. Of the modern anapsids, tortoises are the only living representatives. Turtles were first noted in the Upper Triassic, however, at that time they already had almost all the anatomical features of modern turtles, with the exception of the carapace, that is, their formation should have begun much earlier - in particular, they already had joints inside the rib cage. Most other reptiles with anapsid skulls, including the Millerettids, Nyctifuretes, and Pareiasaurs, died out in the Late Permian in a mass extinction event.

39. Systematics and features of the subclass Scales. scaly(lat. Squamata) - one of the four modern orders of reptiles, including snakes, lizards, as well as lesser-known amphisbaena, or two-legged. Animals of this order are widespread in all parts of the world on the continents and islands; they are absent in the polar and circumpolar regions. The body is covered on top with horny scales, scutes or grains. The quadrate bone is usually movably articulated with the cranium. Of the temporal arches, only one upper one is preserved, or it is also absent. The pterygoids do not articulate with the vomer. The transverse bone is usually present. The teeth are attached to the upper or inner surface of the jaws. The vertebrae are amphicoelous or procoelous. There are two or three sacral vertebrae, if they are expressed. Ribs with one head. The ventral ribs are absent or rudimentary. The pineal opening is present or absent.

40. The external structure of the lizard. Signs associated with the development of land. The body of the lizard is divided into sections: head, trunk, tail, 2 pairs of limbs. The body is covered with dense dry skin with horny scales (there is a molt). The head is oval in shape with large horny shields. On the head are the sense organs, a pair of through nostrils, a mouth with teeth and a long thin tongue. Eyes with movable eyelids. There is a neck. The body is slightly flattened, soft. The tail is long, elastic, can break off and then recover (regenerate). Two pairs of legs are widely spaced on the sides of the body, toes with claws. When moving, lizards crawl - they touch the ground with their bodies.

41. The structure of the circulatory digestive, respiratory and excretory systems of the lizard.The circulatory system of reptiles. Like amphibians, reptiles have two circulations and a three-chambered heart. But unlike amphibians, the ventricle of the reptile heart has a septum that separates it into two parts. One of them receives venous blood, and the other - arterial. Respiratory system reptiles consists of the lungs and airways. The lungs are formed by a large number of cells, so they have a large gas exchange surface. Through the respiratory tract - nasal openings, larynx, trachea, bronchi - air enters the lungs. Digestive system in reptiles (Fig. 39.6) almost the same as in amphibians. However, in the digestion of food in a lizard, not only the substances of the digestive glands are involved, but also beneficial bacteria symbionts. They live in a small outgrowth of the intestine - the caecum. excretory system reptiles consists of the kidneys, ureters and bladder, connected to the cloaca.

42. The structure of the skeleton, nervous system and sensory organs of the lizard. The skeleton of a lizard consists of the same sections as those of amphibians. But in the spine of reptiles, five sections are distinguished: cervical, thoracic, lumbar, sacral and caudal. The first vertebra of the cervical region is connected to the skull so that the lizard can easily turn its head. Like most chordates, the central nervous system of reptiles is represented by the brain (from 5 departments) and the spinal cord. The brain is located inside the skull. A number of important features distinguish the brain of reptiles from the brain of amphibians. Often they talk about the so-called sauropsid type of brain, which is also inherent in birds, in contrast to the ichthyopsid type in fish and amphibians. The olfactory organ is represented by internal nostrils - choanas and vomeronasal organ. Compared to the structure of amphibians, the choanae are located closer to the pharynx, which makes it possible to breathe freely while food is in the mouth. The sense of smell is better developed than that of amphibians, allowing many lizards to find food under the surface of the sand at a depth of up to 6-8 cm. The organ of taste is taste buds located mainly in the throat. The organ of thermal sensitivity is located on the facial fossa between the eye and nose on each side of the head. Especially developed in snakes.

43. The reproductive system of reptiles. Reproduction. The concept of anamnia and amniotes. Reptiles are dioecious animals, bisexual reproduction. male reproductive system consists of a pair of testes that are located on the sides of the lumbar spine. From each testicle departs the seminal canal, which flows into the Wolfian canal. With the appearance of the trunk kidney in reptile wolfs, the canal in males acts only as a vas deferens and is completely absent in females. The Wolffian duct opens into the cloaca to form the seminal vesicle. Reptiles breed on land. Crocodiles, sea snakes and turtles, which are mainly aquatic, are no exception. Fertilization in reptiles is internal. In most species, increased activity is observed during the breeding season: battles of males are not uncommon. Amnion - as an important embryonic adaptation to development in terrestrial life, is formed not only in reptiles, but also in other higher vertebrates in the embryos of birds and mammals. According to the presence or absence of this embryonic organ, all vertebrates can be divided into two groups - into amniotes (Amniota - reptiles, birds and mammals) and anamnia (Anamnia), that is, without amnion (cyclostomes, fish and amphibians).

44. General characteristics of birds, as animals adapted to flight. Birds are warm-blooded vertebrates adapted to flight, therefore the main features of the external and internal organization of their bodies are associated with flight. This is a streamlined "drop-shaped" body shape, and forelimbs in the form of wings, and a body cover of feathers, and powerful muscles on the chest that provide flight. The purpose of the flight is the thinness and pneumaticity of the bones, as well as the disappearance of the heavy dental apparatus and the development of a horny beak instead; the absence of the rectum and bladder, due to which there is no accumulation of waste products inside the body. With the acquisition of the ability of birds to fly, the whole evolution proceeded in the closest connection with this ability of theirs. Paleontological materials show that the ancestors of birds were primitive archosaurs that lived in the Triassic or even in the Permian period. The ancestors of birds were terrestrial running reptiles and, apparently, medium-sized animals.

46. ​​General taxonomy of birds (up to and including orders). Birds, which include about 8,600 species, are the most species-rich class of vertebrates after fish. However, being extremely diverse in the details of the structure, in terms of the main features of the organization, all birds are very homogeneous. In this respect, birds are the exact opposite of reptiles. This is explained by the fact that reptiles are an ancient, almost extinct class, the main modern groups of which, in the process of evolution, managed to disperse far, while birds are the youngest class of vertebrates, which immediately flourished in the latest era of the history of the Earth. The class of birds is divided into two subclasses: lizard-tailed and fan-tailed.

47. General characteristics and biology of the superorder swimming birds. From a biological point of view, the most characteristic features of birds are, on the one hand, the intensity of metabolism, the intensity of the course of life processes, and on the other hand, movement through the air by flight. These two main features of birds largely determine their biology. It is these properties of birds that fundamentally distinguish them from other groups of vertebrates. Despite the common evolutionary origin of birds and reptiles, the biological differences between these two groups of animals are enormous.

49. General characteristics and systematics of the superorder Keel-breasted.Predatory(lat. Carnivora- "carnivores") - detachment (Pinnipedia).

50. The external structure of a dove. Features of the feather cover . The feather cover is inherent only to birds, which is why they are sometimes called birds. The tightly fitting plumage gives the bird's body a streamlined shape. Feather cover, light and warm, serves as a good thermal insulator, promotes incubation of eggs, and individual feathers (primaries and tail feathers) provide the possibility of flight. In the vast majority of birds, plumage does not completely cover the entire surface of the body. The only exceptions are some flightless birds, whose entire body is evenly covered with feathers. The body of a dove is divided into the same sections as those of reptiles - head, neck,torso and limbs. The pigeon's head is small, rounded, with a fairly long and thin head extended forward. beak, dressed in a horn case. The beak consists of two parts: the upper - mandibles and bottom- mandibles. At the base of the mandible open nostrils. On the sides of the head are round eyes, somewhat lower and back from them under the feathers are hidden ear holes. The pigeon's head sits on a movable neck, which allows the bird not only to deftly collect food and look around, but also clean the feathers of the abdomen, wings, back and tail with its beak. The forelimbs are wings that serve for flight: their planes support the bird in the air.

51. The internal structure of a dove as a flying vertebrate. Features in organ systems. The internal structure of the dove is the same as that of other birds. It consists of: digestive, respiratory and excretory systems. Also present: oral cavity, trachea, crop, esophagus, air sac, stomach, lungs, liver, kidneys, pancreas and cloaca. The stomach of pigeons consists of two sections. In the first of them - glandular- secretion of gastric juice, under the influence of which the food softens. Second department - muscular- has thick walls, food is frayed in it. The bones of the jaws are covered on the outside with horny sheaths that form the beak. The beak is diverse in size and shape, depending on the type of food and methods of obtaining it. There are no teeth, and the food is swallowed whole, but if its volume is very large, then the bird can pinch off pieces with its beak. The esophagus can become very distended.

52. Description of the class Mammals as the most progressive and highly organized. Peculiarities. Mammals are the most highly organized class of vertebrates. They are characterized by a high level of development of the nervous system, primarily the brain. Most mammals have a constant high body temperature. The hair cut usually contributes to the preservation of heat. In almost all mammals, the embryo develops in the womb, which gives birth to live babies. All mammals feed their young with milk produced by the mammary glands of the mother (hence the name of the class of mammals). The combination of many progressive features determined the high level of general organization and allowed mammals to spread widely across the Earth. Terrestrial species predominate among them. In addition, there are flying, semi-aquatic, aquatic and soil inhabitants.

53. The main features of the class mammals. reproduction features. The reproduction of mammals differs significantly from that of other vertebrates. A huge number of animals viviparous. The viviparity observed in some reptiles, amphibians, and even fish differs essentially from that of mammals. Hairline, intrauterine development of the embryo, breastfeeding, care for offspring.

54. General taxonomy of the class Mammals. The class of mammals (Mammalia), containing about 4,000 modern species, is divided into 3 subclasses, which differ greatly in volume. have a cloaca and a number of other reptilian features and have survived to this day only in Australia, the fauna of which is generally distinguished by its antiquity. The marsupial subclass (Metatheria) is a relatively small group, its representatives already have a separate anus and give birth to cubs, but they appear underdeveloped and carry their mother in a bag (hence the name of the subclass). Marsupials also survived to our time only in Australia and in South America, the fauna of which, in its antiquity, occupies the next place after the Australian. Finally, the subclass higher, or placental (Eutheria), includes the vast majority of mammals. They are characterized by the fact that the fetus is equipped with a special organ - the placenta, through which it communicates with the mother's body, and the cubs are born more or less well developed. The placental brain has a significantly higher development.

First animals are a small group of species distributed in the Australian region. According to a number of features, the subclass of the first beasts and the infraclass of cloacae are considered the most archaic and primitive among the infraclasses of mammals. infraclass ( Zaglossus) Barton's prochidna ( Zaglossus bartoni)Bruyne's prochidna ( Zaglossus bruijni) the Attenborough prochidna ( Zaglossus attenboroughi)Zaglossus hacketti Zaglossus robustus family family Steropodontidae.

56. General characteristics, characteristics and distribution of marsupials. Systematics. Marsupials (Marsupialia) - a detachment of viviparous mammals, includes 15–16 families: possums, predatory marsupials, marsupial anteaters, bandicoots, marsupial moles, climbing marsupials, coenolests, wombats, jumping marsupials (kangaroos), unites more than 250 species. Marsupials have been known in North America since the Lower Cretaceous, apparently descended from panthotheres. In Europe, they existed from the Eocene to the Miocene and were replaced by placental animals. Marsupials are divided today into two superorders with 7 modern orders. Superorder (Marsupialia). A hallmark of placental is the birth in a relatively advanced stage. This is possible due to the presence of the placenta, through which the embryo receives nutrients and antibodies from the mother and gets rid of waste products.

58. The external structure of mammals, on the example of a representative. In the body of mammals, the same sections are distinguished as in other terrestrial vertebrates: head, neck, trunk, tail and two pairs of limbs. The limbs have departments typical of vertebrates: shoulder (thigh), forearm (shin) and hand (foot). The legs are not located on the sides, as in amphibians and reptiles, but under the body. Therefore, the body is raised above the ground. This expands the possibilities in the use of limbs. Among the animals known climbing trees, plantigrade and digitigrade animals, jumping and flying.

59. Progressive features of the internal structure of mammals, system by system. The internal structure of insects- this is a set of features of the structure and location of organs by which representatives of this class differ from other living organisms. Insect organs are located in the body cavity - its internal space, which is divided by level into three sections, or sinus. This separation is possible due to the presence of horizontal partitions (diaphragms) in the cavity. The superior or dorsal diaphragm delimits the pericardial region, inside which is the dorsal vessel (heart and aorta). The lower diaphragm separates the space of the perineural sinus; it contains the ventral nerve cord. Between the diaphragms is the widest visceral (visceral) section, in which the digestive, excretory, reproductive systems and structures of the fat body lie. Elements of the respiratory system are found in all three departments.

Chordates are the highest type of the animal kingdom, uniting more than 43,000 species very diverse in size, appearance and habitat. Most of them have an internal cartilaginous or bony skeleton and are called vertebrates. The structural plan of vertebrates sharply distinguishes them from animals of other types, in connection with which the question of the origin of vertebrates remained unresolved for a long time. The merit of clarifying this issue belongs to the Russian scientist-embryologist A.O. Kovalevsky (1840-1901). Having studied the development of the embryos of some primitive marine animals - the lancelet and ascidians, he showed that they are transitional forms that combine the features of invertebrates and vertebrates.

Thanks to this, A. O. Kovalevsky managed to overcome the abyss that separated vertebrates from the lower groups of the animal world, and shed light on their origin. At present, vertebrates, together with transitional forms, are combined into a single type of chordates.

Type characteristic

Despite the diversity of species, all chordates have a common structural plan and differ from representatives of other types in the following four main features.

1. They have an internal axial skeleton, represented by a dorsal string, or chord (chorda dorsalis). The chord is an elastic flexible rod. It develops from the endoderm, consists of highly vacuolated cells and is surrounded by a connective tissue membrane. In lower chordates, it persists throughout life (lancelets, sturgeons, lungfish and lobe-finned fish), in higher chordates (i.e., in most vertebrates), the chord is present only in larvae or embryos, and then is replaced by a cartilaginous or bone formation - the spine . The spinal column consists of individual vertebrae, which are formed in the connective tissue sheath of the notochord during ontogenesis.
2. The central nervous system is located on the dorsal side above the notochord. It looks like a tube stretching along the body, and has an internal cavity - a neurocoel. The central nervous system develops from the ectoderm and differentiates in vertebrates into the brain and spinal cord. In all invertebrates, the nervous system is located on the ventral side of the body and is a chain of nerve nodes connected by nerve cords.
3. The digestive system is located under the chord, it begins with the mouth and ends with the anus (anus). The anterior (pharyngeal) section of the digestive tube has a number of through holes - the gill apparatus. It is represented by gill slits that perforate the wall of the pharynx, and a skeleton that supports the gill slits (visceral arches). The gill apparatus, as well as the notochord, is not preserved in all adult animals. Gill slits are characteristic of fish throughout their lives and are supplemented by special organs of water respiration - gills; in others, they are present only in the larval state (amphibian tadpoles); in terrestrial vertebrates, gill slits form in embryos, but soon overgrow, the respiratory organs - the lungs - develop as paired protrusions on the ventral side of the back of the pharynx.

   The notochord, neural tube and intestines stretch along the entire body and make up a complex of axial organs.

4. The circulatory system is closed. The central organ of blood circulation - the heart or a pulsating blood vessel replacing it - is located on the ventral side of the body and is laid in the embryo under the chord and digestive tube.

In addition to these main signs of chordates, they are very characteristic of the mutual arrangement of the nervous, supporting and digestive systems. In other types of the animal kingdom, there is no such strict pattern (remember the location of the corresponding systems of round and annelids, arthropods, mollusks).

At the same time, chordates have features in common with non-chordates. All chordates are bilaterally symmetrical, have a metameric organ anlage, a secondary body cavity, and a secondary mouth.

The oral opening is formed by breaking through the wall of the gastrula. At the site of the opening of the gastrula (gastropore), an anus is formed. This feature combines chordates, echinoderms, and a few closely related types into a group of deuterostomes. The remaining types considered earlier (with the exception of unicellular ones) are combined into the group of protostomes.

The main organ systems of chordates, including the skeleton, muscles, nervous system, excretory organs, etc., are formed metamerically in embryos. Metamerism is especially pronounced in the embryonic period.

The chordate type is divided into 3 subtypes.

• Subphylum Tunicata (tunicates).

The first two subtypes include a small number of primitive marine animals that lead a sedentary or immobile lifestyle and lack a vertebral column. There are no hullers in the program for university applicants. Non-cranial have a structure of the nervous system typical of chordates in the form of a neural tube, however, its anterior part is not expanded and is not protected by any cartilage or bone formation, i.e., there is no brain and skull. The non-cranial subtype includes one class of simply arranged animals - lancelets. These are not numerous (only about two dozen species) marine animals.

When characterizing the lancelet, pay attention to the features that make it related to lower invertebrate animals: the absence of a brain, real sensory organs and a heart, the absence of paired limbs, and the primitive structure of the excretory organs. On the other hand, signs of a progressive organization should be emphasized: the presence of a true notochord and a tubular nervous system typical of chordates, as well as a closed circulatory system. These features suggest that the lancelet and vertebrates had a common ancestor, which was probably similar to non-cranial animals.

The fourth subtype is the most numerous. It combines highly organized animals with a cartilaginous or bone skeleton. The anterior part of the neural tube is expanded, forming the brain, which is protected by a cartilaginous or bony skull. The part of the neural tube that fits in the body and is called the spinal cord is enclosed, together with the notochord, in a cartilaginous or bony spine, consisting of individual vertebrae. There is a circulatory organ - the heart, which lies on the ventral side of the body, as well as complex kidneys. In addition, well-developed paired limbs (except for cyclostomes) and perfect sense organs (sight, hearing, smell, etc.) are characteristic of vertebrates. All this provides vertebrates with high mobility, the ability to navigate in space, and easily find prey.

The vertebrate subphylum is divided into six classes: cyclostomes, fish, amphibians (amphibians), reptiles (reptiles), birds, and mammals. The applicant is required to know the last five classes. Their brief description is given in Table. 16.

Lecture: chordate animals. Characteristics of the main classes

Evolutionarily, this taxon is the youngest. Today there are 60 thousand species.

Distinctive features of their structure and metabolism are:

1. The presence of an elastic rod-chord or a full-fledged spine;

2. The neural tube is located on the dorsal side of the body, forming the spinal cord;

3. Developed brain;

4. Oxygen respiration;

5. The intestine does not enter the tail section.

Among the chordates there are marine inhabitants, as well as species living on land, in the soil, in the air.

lancelets

These are marine animals of a primitive structure. Many scientists consider them as a transitional group from invertebrates to vertebrates.

The structural features of this animal are:

thin chord;

the presence of gills;

located in the dorsal part of the body neural tube.

The lancelet has a translucent body, on the back and ventral side, as well as the end of the tail, there are fins, the main function of which is movement and maintaining balance in the water. The skin is thin, one-layer. The central nervous system is represented by a single tube. There is no differentiation between spinal cord and brain. The tentacles located around the mouth are used as sensory organs. There are simply arranged light-sensitive eyes. The skeleton is represented by a chord, along which are strands of muscles.

The pharynx can occupy up to a third of the length of the body, and gill slits are also located in it. The intestine is primitive, undifferentiated, ending in an anus. There is a hepatic outgrowth that secretes enzymes. The excretory system is similar to that of annelids - a system of convoluted tubules, metabolic products are excreted through the gills. The lancelet breathes the entire surface of the body. The circulatory system is developed, partially closed, there are vessels. Lancelets are dioecious, fertilization is external. The eggs develop in an aquatic environment.

Fish

A characteristic feature is the presence of developed jaws and gill breathing. The outer covers are leather. In bony it is covered with scales, in cartilaginous it is naked, with rows of plaques. They can move with the help of fins.

The spinal cord is located inside the spine. There are ribs. The brain consists of five sections. Along the body is the organ of tactile senses - the lateral line. Eyes of complex structure. There are organs of taste and smell. The organs of hearing are paired. Most representatives have a single circle of blood circulation and a two-chambered heart.

Fish grab food with their mouths, tear them apart and hold them with their teeth. The lump enters the throat, then through the esophagus into the stomach. The anal opening is located in the region of the posterior pelvic fins. The body of the fish maintains its osmotic pressure by excreting excess salts by the kidneys.

Fish are bisexual for the most part, hermaphrodites are rare, some of them are capable of self-fertilization. Mating behavior is quite complex - nests are built where eggs are laid. Fertilization is external.

Amphibians

This is a relatively small taxon of animals adapted to living on land and in water. For reproduction, most species require a reservoir, since in the larval stage the amphibian lives in the aquatic environment.

The skin is thin and smooth, it is easily permeable to gases and liquids, and is equipped with a huge number of capillaries for additional gas exchange. It contains many mucus-producing glands. The skeleton has a complex structure, divided into the spine, skull and limbs. The muscle system has a rather complex structure, providing mobility. Respiratory organs are gills, lungs and skin.

The circulatory system consists of two circles of blood circulation, the heart is three-chambered (two atria and one ventricle). The metabolic rate is low, the animals are completely dependent on the external temperature, they are cold-blooded. All amphibians are predators. The trapping organ is a long tongue. The intestines are divided into sections and open into the cloaca. The excretory system is represented by the kidneys and the bladder, which has an outlet to the cloaca. Some substances are removed through the skin.

The brain is larger than that of fish, there are nerve plexuses in the area of ​​​​the shoulders and lower back. The eyes are adapted to the atmospheric environment, equipped with eyelids. There are two olfactory sacs. The hearing aid is quite complex structure, there is a tympanic membrane and a middle ear. The skin contains many nerve endings and is the organ of touch.

All species have separate sexes, fertilization is external. The development is complex, stage by stage - egg, larva, metamorphosis, adult. Eggs are laid in water by most species.

reptiles

In this taxon, mainly terrestrial species are represented, the distinctive features of which are:

dry skin covered with scales or scutes;

more pronounced division of the spine into sections. The head can turn;

all but snakes have a chest, there are intercostal muscles that provide breathing.

The developed nervous system, the brain consists of 5 departments. There are 6 sense organs. Breathing is pulmonary. The heart is three-chambered, a partial septum appears in it, separating venous and arterial blood. A more complex gastrointestinal tract, where differentiation into departments is more pronounced. Excretory system in the form of kidneys, bladder and cloaca. Reproduction is bisexual, with internal fertilization. The embryo develops in an egg equipped with a leathery or calcareous shell. Some species have live birth. The development is direct. There is care for offspring.

Birds

This is a class of egg-laying warm-blooded animals adapted to flight in the atmosphere. In this regard, there were qualitative changes in the structure of the body:

forelimbs in the form of wings;

lightweight skeleton, the presence of a pectoral keel and powerful muscles;

the presence of a feather cover;

powerful respiratory system consisting of lungs and five pairs of air sacs;

streamlined body shape;

the presence of a beak;

four-chambered heart;

there are no teeth, food is crushed in the stomach, for which the bird swallows sand and pebbles;

fast metabolism.

A very developed brain with a large cerebellum that controls body position and motor activity. Complex intellectual behavior.

Reproduction is bisexual, fertilization is internal. The embryo develops in the egg. Most species are monogamous. Marriage behavior is complex.

Birds are important contributors to ecosystems. They contribute to the spread of plants by spreading seeds, predators regulate the number of small animals.

mammals

The most evolutionarily young and progressive taxon. It has a number of fundamental differences from all other animals:

Live birth (except for the first animals) and feeding offspring with milk;

Real warm-bloodedness;

Strong development of sebaceous and sweat glands;

Division of the internal cavity of the body into two by a diaphragm;

High development of the nervous system;

differentiated teeth.

Representatives of this class are capable of higher nervous activity, an active lifestyle.

Type Chordates combines animals that are very diverse in appearance, lifestyle and living conditions. Representatives of chordates are found in all the main environments of life: in water, on the land surface, in the thickness of the soil and, finally, in the air. They are geographically distributed throughout the world. The total number of species of modern chordates is approximately 40 thousand. The Chordata type includes non-cranial (lancelets), cyclostomes (lampreys and hagfish), fish, amphibians, reptiles, birds and mammals.

As shown by the brilliant studies of A. O. Kovalevsky, the chordates also include a peculiar group of marine, largely sessile, animals - tunicates (appendicularia, ascidians, salps). Some signs of similarity with chordates are found by a small group of marine animals - enteropneusta, which are sometimes also included in the chordate phylum.

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, initially appearing 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 displaced by the vertebrae, in connection with this, the axial skeleton becomes segmented from a continuous non-segmented cord. The spine, like all other skeletal formations (except the chord), is of mesodermal origin and is formed from a connective tissue sheath surrounding the chord 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 cerebrum. 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.

3. The anterior (pharyngeal) section of the digestive tube communicates with the external environment with two rows of holes, called visceral fissures. 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 the indicated three main features of chordates, the following characteristic features of their organization should be mentioned, which, however, besides chordates, representatives of some other groups also have. chordates, as well as