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 progenitors 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 to be one of the most important stages in the development of the historical animal world.

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, jawless ones also formed, from which 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 came to land, and thus a new species appeared - 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.

The respiratory system in lower chordates is represented by gills, while in vertebrates it is represented 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 the mouth, 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. At the moment, there are about 50 thousand species of chordates. The presence of a common feature in all individuals - the chord (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.

More than 40 thousand modern species of animals are classified as chordates. These animals are very diverse in external structure, lifestyle and living conditions.

General features of the structure of chordates:

• The presence of an internal axial skeleton, the basis of which is a dense, elastic and elastic dorsal cord - chord. It occurs in all chordates in the early stages of development of their embryos(in lower chordates, it persists throughout life, in higher ones it exists only in embryos, in adults it is replaced by a spine).
• The nervous system looks like tubes located on the dorsal side - over the chord ( formed from a layer ectoderm). In higher chordates anterior neural tube grows and forms the brain.
• All chordates - bilaterally symmetrical animals. Runs along their body digestive tube- Intestine that starts at the mouth and ends at the anus.
• All chordates in embryonic development have gill slits - paired transverse openings penetrating the anterior part of the digestive tube.
• Circulatory system chordates closed. A heart located on the ventral side of the body under the alimentary canal.

The phylum Chordates includes three subtypes: Non-cranial, Tunicates, and Vertebrates (Cranial).

Subtype Cranial It is represented by a small group of marine chordates and includes one class - Lancelet, which includes about 30 species of small animals. The name "skullless" suggests that representatives of this subtype do not have a skull or brain. The structure of the non-cranial is quite primitive:

• The notochord serves as their internal skeleton throughout their lives.
• The functions of the central nervous system are performed by the neural tube.

Subtype Shellers (Larval chordates, or Tunicates), includes about 1500 species of marine chordates. The tunicates the main features of the Chordata type are clearly expressed only at the larval age.

At the initial stage of life, tunicates are free-swimming larvae that move with the help of a tail. The larvae of the tunicates have a complex structure similar to that of the lancelet. As the larva develops into an adult, its structure is simplified. In adulthood, most of them lack the notochord and neural tube. The body of an adult tunic is enclosed in a gelatinous shell - a tunic - and resembles a bag with two funnels through which water enters and exits. With water, the animal receives oxygen for breathing and food - organic particles. The tunicates are hermaphrodites. Many species reproduce by budding, forming colonies.

Subtype Vertebrates unites most species of chordates. For this subtype Classes include: Cartilaginous fishes and Bony fishes, Amphibians, Reptiles, Birds and Mammals. In terms of structure and lifestyle, vertebrates are at a higher level of organization than non-cranial and tunicates.

In contrast to the sedentary and passively feeding non-cranial ancestors of vertebrates, they switched to an active search for food and movement associated with it. This led to the development of a powerful internal skeleton and muscles, the improvement of the processes of respiration, nutrition, blood circulation, excretion, sensory organs and the central nervous system.

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 a 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, shaped like fish, 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 that live in shallow water. A typical representative is Lancelet - Branchiostoma lanceolatum(genus Lancelets, class Headochords, subtype Cranial, type Chordates), whose dimensions reach 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 - Cephalochordidae. 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 sent 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, with 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, locals 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 unites more than 40 thousand species of animals, differing in appearance, lifestyle and living conditions. Despite the great diversity, representatives of this type have similar, unique features:

a) The presence of an axial skeleton. Initially, it appears in the form of a dorsal string - a chord, which is a flexible elastic cord. The chord is preserved for life only in the lower chordates, and in the higher it is replaced by the vertebral column.

b) The central nervous system looks like a neural tube with a narrow channel inside. It is located on the dorsal side of the animal's body above the axial skeleton (chord or vertebral bodies - spinal canal).

c) The presence of gill slits in the wall of the pharynx, which in primary aquatic animals persist throughout life, while in the rest they are found only at the embryonic stages of development.

In addition, chordates are characterized by:

a) The presence of a coelom (secondary body cavity);

b) Secondary;

c) Bilateral symmetry of the body;

d) Closed circulatory system, the heart is located on the ventral side of the body;

e) The skin has a two-layer structure, consists of the epidermis and dermis.

The Chordata phylum includes three subtypes: Tunicates, Bes-cranial (cephalochordates) and Cranial (vertebrates).

2. Features of the structure and biology of the lancelet.material from the site

The non-cranial are a small group of primitive chordate animals in which all the main features of the type are preserved throughout their lives. They live exclusively in the seas, where they lead a bottom lifestyle, burrowing into the sand. A typical representative is the lancelet. This is a small translucent animal 5-8 cm long with a narrow, laterally flattened body. The head is not isolated. The narrow dorsal fin smoothly passes into the tail, which has a lanceolate shape. At the front end is a mouth funnel surrounded by tentacles. With their help, the lancelet constantly passes water through the pharynx, filtering out food particles. At the same time, water washes numerous gill slits, in the partitions of which gas exchange occurs. The circulatory system consists of two large blood vessels (abdominal and spinal) and small vessels extending from them. There is no heart. The blood flow is created by the pulsation of the abdominal vessel. The excretory organs are represented by numerous modified metanephridia (about 90 pairs). Lancelets are dioecious. Fertilization is external. The development of the larva lasts about three months. The study of the structure of non-cranial sheds light on the origin of chordates. The lancelet can be considered an intermediate form between the ancient annelids and modern vertebrates.

The main features of the type of chordates

The main features of the chordate type are, firstly, the presence of an axial skeleton in the form of a chord lying above the intestines; secondly, the presence of gill slits in the pharyngeal wall, which persist throughout life in aquatic forms, while in terrestrial forms with pulmonary respiration only in the early stages of embryonic development; thirdly, this is the location of the neural tube - the central nervous system on the dorsal side of the body above the chord. These three features are common to all chordates.

Chordate type classification

We already know that lancelets do not have a brain and, accordingly, they do not have a skull, so they are distinguished into a group non-cranial chordates. Their axial skeleton (weak dorsal string - chord) is preserved throughout life. Chordate animals that have a brain protected by a skull, and instead of a notochord, a spine consisting of cartilaginous or bone vertebrae, are combined into a group cranial, or vertebrates. Their brains developed from the anterior neural tube, and their skulls developed from fused together anterior vertebrae.

About 20 species of non-cranial are known. There are more than 40,000 species of living vertebrates today.

Vertebrates are divided into 6 classes. The first class is cartilaginous fish, the second is skeletal fish. All fish are aquatic vertebrates, their habitat is rivers, lakes, seas. The vertebrates of the third class, the amphibians (frogs, toads, newts), descended from the ancient fishes. They live both in water and on land. In water, they breed and spend the beginning of their lives. Ancient amphibians are the ancestors of animals belonging to the fourth class - reptiles (snakes, lizards, turtles, crocodiles). Reptiles are completely terrestrial vertebrates that breed on land. Even those of them who have mastered the aquatic environment again, such as the sea turtle, crawl out to lay their eggs on land. The fifth class is birds. The sixth class is mammals, or beasts. Both birds and mammals are descendants of ancient reptiles - lizards. Birds that have mastered the air space reproduce with eggs, and mammals feed their offspring with milk.

Common features of vertebrates

In all vertebrates, the notochord was replaced in the process of historical development by the spine (hence their name), consisting of a number of movably articulated cartilaginous (in cartilaginous fish) and bony (in other classes of vertebrates) vertebrae. Respiratory system- or gills, or lungs. They are small in volume but have a large surface area. Nutrients and oxygen are delivered to the organs through a closed circulatory system. The pulse of the heart is used to move blood. Metabolic products are excreted by the kidneys.

There are 5 main sense organs: touch, sight, hearing, smell and taste. The activity of all organs is coordinated by the brain. It is protected by a skull. Vertebrates are mobile animals. Their metabolic processes proceed intensively. Due to the high mobility of the central nervous system, the brain reaches special perfection in vertebrates. Therefore, they are able to quickly respond to changing environmental conditions. Their activity is based not only on innate, unconditioned reflexes, instincts, but also on acquired, conditioned reflexes. The more diverse the lives of certain vertebrates, the more developed their brain is and the sooner and easier they form new conditioned reflexes.

Classes of vertebrates occurred in different historical periods in the development of life on Earth. Therefore, the height of their organization is different.

Significance of vertebrates

Vertebrates play a big role in nature, as they are an important link in nature. Often they close the food chain: plants - invertebrates - vertebrates. Their significance for a person is very great. They provide the bulk of animal protein consumed by humans, a significant part of fats, as well as various non-food products - leather, feathers, wool.

Most domesticated animals (with the exception of the honey bee and silkworm), as well as all animals bred by man, are vertebrates.