General structural features of chordates. Phylum Chordata

Lecture: Chordates. Characteristics of the main classes

Chordates

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 spine;

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

3. Developed brain;

4. Oxygen breathing;

5. The intestine does not extend into the caudal region.

Among chordates there are marine inhabitants, as well as species living on land, in soil, and 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;

presence of gills;

neural tube located in the dorsal part of the body.

The lancelet has a translucent body; fins are located on the back and ventral side, as well as the end of the tail, the main function of which is to move and maintain balance in the water. The skin is thin, single-layer. Central nervous system represented by one tube. There is no differentiation between the spinal cord and the 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 notochord, with cords of muscles located along it.

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

Fish

A characteristic feature is the presence of developed jaws and gill breathing. The outer covering is skin. In bony animals it is covered with scales, in cartilaginous animals it is bare, 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. An organ is located along the body tactile senses- lateral line. Eyes of complex structure. There are organs of taste and smell. The hearing organs are paired. Most representatives have a single circulation and a two-chambered heart.

The fish grabs food with its mouth, tears it apart and holds it with its teeth. The lump enters the throat, then through the esophagus into the stomach. Anal hole located in the area of ​​the posterior ventral fins. The fish body maintains its osmotic pressure by secreting extra salts kidneys.

Most fish are bisexual; 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 body of water, since in the larval stage the amphibian lives in an 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 complex structure, dividing into the spine, skull and limbs. The muscle system has a rather complex structure, providing mobility. The respiratory organs are gills, lungs and skin.

The circulatory system consists of two circulation circles, the heart has three chambers (two atria and one ventricle). The metabolic rate is low, animals are completely dependent on the temperature of the external environment, and are cold-blooded. All amphibians are predators. The catching organ is the long tongue. The intestine is divided into sections and opens into the cloaca. The excretory system is represented by the kidneys and bladder having an outlet into the cloaca. Some substances are removed through the skin.

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

All species are dioecious, fertilization is external. Development is complex, stage-by-stage - egg, larva, metamorphosis, adult. Eggs are laid in water by most species.

Reptiles

This taxon contains predominantly terrestrial species, distinctive features of which is:

dry skin covered with scales or scutes;

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

everyone except snakes have rib cage, there are intercostal muscles that provide breathing.

A developed nervous system, the brain consists of 5 sections. 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 viviparity. Development is direct. There is concern for the offspring.

Birds

This is a class of oviparous warm-blooded animals adapted for flight in the atmosphere. In this regard, qualitative changes in the structure of the body occurred:

forelimbs in the form of wings;

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

presence of 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 characterized by monogamy. Marital behavior is complex.

Birds are important participants in ecosystems. They promote the spread of plants by distributing seeds; predators regulate the number of small animals.

Mammals

The youngest and most progressive taxon. Has a number fundamental differences from all other animals:

Viviparity (except for first animals) and feeding offspring with milk;

True warm-bloodedness;

Strong development of sebaceous and sweat glands;

Separation internal cavity torso with two diaphragms;

High development of the nervous system;

Differentiated teeth.

Representatives of this class are capable of higher nervous activity, active image life.

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

General structural features of chordates:

• Presence of an internal axial skeleton, the basis of which is a dense, elastic and elastic dorsal cord - chord. It is formed in all chordates on early stages development of their embryos(in lower chordates it persists throughout life, in higher chordates it is present only in embryos, in adults it is replaced by a spine).
• The nervous system looks like tubes, located on the dorsal side - above the chord ( formed from a layer ectoderm). In higher chordates anterior section neural tube grows and forms the brain.
• All chordates - bilaterally symmetrical animals. Runs along their body digestive tube - the intestine, starting with the mouth and ending with the anus.
• In embryonic development, all chordates have gill slits - paired transverse openings that penetrate the anterior section of the digestive tube.
• Circulatory system chordates closed. Heart located on the ventral side of the body under the alimentary canal.

The phylum Chordata includes three subphyla: Aneschunates, Tunicates, and Vertebrates (Cranials).

Subtype Skullless is represented by a small group of marine chordates and includes one class - Lancelets, 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 skullless 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 Tunicates (Larval chordates, or Tunicates), includes about 1,500 species of marine chordates. In tunicates the main characters of the Phylum Chordata are clearly expressed only in the larval age.

On initial stage In life, tunicates are free-swimming larvae that move with the help of their tail. Tunicate larvae have a complex structure similar to that of the lancelet. As the larva develops into an adult, its structure becomes simpler. As adults, most of them do not have a notochord or neural tube. The body of an adult tunicate is enclosed in a gelatinous membrane - 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. Tunicates are hermaphrodites. Many species reproduce by budding, forming colonies.

Subphylum Vertebrates unites most species of chordates. To this subtype include Classes: Cartilaginous fish and Bony fish, Amphibians, Reptiles, Birds and Mammals. In terms of structure and lifestyle, vertebrates are more high level organizations than the skullless and tunicates.

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

general characteristics phylum Chordata

Basic terms and concepts tested in the examination paper: skullless, gill slits, internal skeleton, amphibians, skin, limbs and limb girdles, circulatory circles, lancelet, mammals, neural tube, vertebrates, reptiles, birds, reflexes, adaptations to lifestyle, fish, bony skeleton, cartilaginous skeleton, notochord.

TO phylum Chordata These include animals that have an internal axial skeleton—notochord or vertebral column. In the process of evolution, chordates reached the highest level of organization and flourishing, compared to other types. They live in all areas globe and occupy all habitats.

Chordata- These are bilaterally symmetrical animals with a secondary body cavity and a secondary mouth.

In chordates it is observed overall plan structure and location of internal organs:

– the neural tube is located above the axial skeleton;

– there is a chord under it;

– the digestive tract is located under the notochord;

– under the digestive tract is the heart.

In the phylum Chordata, there are two subtypes - Cranial and Vertebrate. Refers to the skullless lancelet. All other chordates known today and considered in a school biology course belong to the subphylum Vertebrates.

The subtype Vertebrates includes the following classes of animals: Fish, Amphibians, Reptiles, Birds, Mammals.

General characteristics of chordates. Skin vertebrates protect the body from mechanical damage and other environmental influences. The skin is involved in gas exchange and removal of decay products.

Derivatives of the skin include hair, claws, nails, feathers, hooves, scales, horns, needles, etc. Sebaceous and sweat glands develop in the epidermis.

Skeleton, representatives of the chordate type can be connective tissue, cartilaginous and bone. The skullless have a connective tissue skeleton. In vertebrates – cartilaginous, osteochondral and bone.

Musculature– divided into striated and smooth. Striated muscles are called skeletal muscles. Smooth muscle forms muscular system jaw apparatus, intestines, stomach and other internal organs. Skeletal muscles are segmented, although less so than in lower vertebrates. Smooth muscle has no segmentation.

Digestive system presented oral cavity, pharynx, always connected with the respiratory organs, esophagus, stomach, small and large intestines, digestive glands– the liver and pancreas, which develop from the wall of the anterior intestine. During the evolution of chordates, the length digestive tract increases, it becomes more differentiated into departments.

Respiratory system formed by gills (in fish, amphibian larvae) or lungs (in terrestrial vertebrates). For many, the skin serves as an additional respiratory organ. The gill apparatus communicates with the pharynx. In fish and some other animals it is formed gill arches, on which the gill filaments are located.

Lungs in progress embryonic development are formed from intestinal outgrowths and are of endodermal origin.

The circulatory system is closed. The heart consists of two, three or four chambers. Blood enters the atria and is sent into the bloodstream by the ventricles. There is one circulation (in fish and amphibian larvae) or two (in all other classes). The heart of fish and amphibian larvae is two-chambered. Adult amphibians and reptiles have a three-chambered heart. However, in reptiles there appears incomplete interventricular septum. Fish, amphibians and reptiles are cold-blooded animals. Birds and mammals have a four-chambered heart. These are warm-blooded animals.

Blood vessels are divided into arteries, veins and capillaries.

Nervous system ectodermal origin. It is laid in the form of a hollow tube on the dorsal side of the embryo. The central nervous system is formed by the brain and spinal cord. The peripheral nervous system is formed by the cranial and spinal nerves and interconnected nerve ganglia, lying along spinal column. Spinal cord is a long cord lying in the spinal canal. From spinal cord spinal nerves emerge.

Sense organs well developed. Proto-aquatic animals have organs side line, perceiving pressure, direction of movement, speed of water flow.

Excretory organs in all vertebrates they are represented by the kidneys. The structure and mechanism of functioning of the kidneys changes during the process of evolution.

Reproductive organs. Vertebrates are dioecious. The gonads are paired and develop from the mesoderm. The reproductive ducts are connected to the excretory organs.

Superclass Pisces

Fish appeared in the Silurian - Devonian from jawless ancestors. There are about 20,000 species. Modern fish are divided into two classes - Cartilaginous And Bone. Cartilaginous fish include sharks and rays, characterized by a cartilaginous skeleton, the presence of gill slits, and the absence of a swim bladder. Bony fish include animals that have bony scales, a bony skeleton, and gill slits covered by an operculum. The appearance of fish is due to the following aromorphoses :

– the appearance of a cartilaginous or bone spine and skull, covering the spinal cord and brain on all sides;

– appearance of jaws;

– the appearance of paired limbs – ventral and pectoral fins.

All fish live in water and have a streamlined body, divided into a head, body and tail. Well-developed sense organs - vision, smell, hearing, taste, lateral line organs, balance. The skin is two-layered, thin, mucous, covered with scales. The muscles are almost undifferentiated, with the exception of the muscles of the jaws and the muscles attached to the gill covers of bony fish.

Digestive system well differentiated into departments. There is a liver with gallbladder and pancreas. Many have developed teeth.

Respiratory organs fish are gills, and lungfish have gills and lungs. An additional function of respiration is performed by the swim bladder in bony fish. It also performs a hydrostatic function.

Circulatory system closed. One circle of blood circulation. The heart consists of an atrium and a ventricle. Deoxygenated blood from the heart through the afferent gill arteries it enters the gills, where the blood is saturated with oxygen. Arterial blood through the efferent branchial arteries they enter the dorsal aorta, which supplies blood internal organs. Fish have a portal system of the liver and kidneys, which cleanses the blood of harmful substances. Fish are cold-blooded animals.

Excretory system represented by ribbon-shaped primary buds. Urine flows through the ureters into bladder. In males, the ureter is also the vas deferens. Females have an independent excretory opening.

Gonads represented by paired testes in males and ovaries in females. Many fish exhibit sexual dimorphism. Males are brighter than females, attracting them with their appearance and mating dances.

In the nervous system The development of the diencephalon and midbrain should be noted. Most fish have a well-developed cerebellum, which is responsible for coordinating movements and maintaining balance. The forebrain is less developed than in higher classes of animals.

Eyes They have a flat cornea and a spherical lens. Century no.

Hearing organs presented inner ear – membranous labyrinth. There are three semicircular canals. They contain limestone stones. Fish make and hear sounds.

Organs of touch represented by sensory cells scattered throughout the body.

Side line perceives the direction of flow and water pressure, the presence of obstacles, and sound vibrations.

Taste cells are located in the oral cavity.

The importance of fish in nature and human life. Consumers of plant biomass, consumers of the second and third orders; sources food products, fats, vitamins.

EXAMPLES OF TASKS

Part A

A1. Skullless animals include

3) lancelet

4) octopus

A2. The main characteristic of chordates is

1) closed circulatory system

2) internal axial skeleton

3) gill breathing

4) striated muscles

A3. Has a bony skeleton

1) white shark 3) stingray

2) katran 4) piranha

A4. Warm-blooded animals include

1) whale 2) sturgeon 3) crocodile 4) toad

A5. Bony gill covers are present in

1) dolphin 3) tuna

2) sperm whale 4) electric stingray

A6. Has a four-chambered heart

1) turtles 2) pigeons 3) perches 4) toads

1) single-chamber heart and two circles of blood circulation

2) two-chambered heart and one circulation

3) three-chambered heart and one circulation

4) two-chambered heart and two circles of blood circulation

A8. Cold-blooded animals include

1) beaver 3) squid

2) sperm whale 4) otter

A9. Coordination of fish movements is regulated

1) forebrain 3) spinal cord

2) midbrain 4) cerebellum

A10. Doesn't have a swim bladder

1) katran 2) pike 3) perch 4) sturgeon

Part B

IN 1. Choose the correct statements

1) fish have a three-chambered heart

2) the transition of the head to the body in fish is clearly visible

3) in the organs of the lateral line of fish there are nerve endings

4) the notochord in some fish remains throughout life

5) fish are not capable of education conditioned reflexes

6) the nervous system of fish consists of the brain, spinal cord and peripheral nerves

AT 2. Select signs related to skullless animals

1) the brain is not differentiated into sections

2) the internal skeleton is represented by a chord

3) excretory organs - kidneys

4) the circulatory system is not closed

5) the organs of vision and hearing are well developed

6) the pharynx is penetrated by gill slits

VZ. Establish a correspondence between the characteristics of animals and the type to which these animals belong

Part C

C1. Where can deep-sea fish store oxygen? Why do they need to do this?

C2. Read the text carefully. Indicate the numbers of sentences in which errors were made. Explain and correct them.

1. The chordate phylum is one of the largest in terms of the number of species in the animal kingdom. 2. The internal axial skeleton of all representatives of this type is the notochord - a bony, dense, elastic cord 3. The type Chordata is divided into two subtypes - Vertebrates and Invertebrates. 4. In the nervous system, the anterior part of the brain receives the greatest development. 5. All chordates have radial symmetry, a secondary body cavity, and a closed circulatory system. 6. An example of primitive chordates is the lancelet.

Chordata ( Chordata listen)) is a phylum of animals that includes vertebrates, larvalochordates, and anecranates. Vertebrates such as birds and fish are the most famous, and are the subphylum of animals to which humans belong.

Chordates have bilateral symmetry, which indicates the existence of a line of symmetry dividing their body into two halves, which are almost mirror images of each other.

Bilateral symmetry is found not only in chordates, but also in (although in the case of echinoderms they are bilaterally symmetrical only during the larval stage of their life cycle, and in adults pentaradial symmetry appears).

All chordates have a notochord, which is present for some or all of their life cycle. The chord (or dorsal string) is a semi-flexible rod to which big muscles animal. It also plays an important role in signaling and coordinating development.

The notochord consists of flat chordae enclosed in a fibrous sheath. In vertebrates, the dorsal chord is present only during the embryonic stage of development, and then the vertebrae develop around it and form the spine. In tunicates, the notochord remains throughout the animal's life cycle.

Chordata have a single, hollow dorsal nerve cord that runs down the animal's back and, in most species, forms the brain at the front of the body. They also have gill slits, which serve as openings between the pharyngeal cavity and external environment, and also for filtering water.

Another characteristic of chordates is a structure called the endostyle, a groove-like organ that lies against the wall of the pharynx and secretes mucus and traps small food particles that enter the pharyngeal cavity. The endostyle is present in tunicates and lancelets. In vertebrates, the endostyle is replaced thyroid gland - endocrine gland located in the neck.

Main characteristics

• chord;
• neural tube (cord);
• gill slits;
• endostyle or thyroid gland;
• muscle tail.

Species diversity

The phylum chordata includes more than 75,000 species of animals.

Classification

Chordata are classified in the following taxonomic hierarchy:

• Domain: Eukaryotes ( Eukaryota);
• Kingdom: Animals ( Animalia);
• Type: Chordata ( Chordata).

Chordates, in turn, are divided into the following subphyla:

• Skullless ( Acrania) : There are now about 32 species of skullless. Representatives of this subphylum have notochords that persist throughout their life cycle. Lancelets are the only family of skullless fish whose members are marine animals with long, narrow bodies. Earliest known fossil lancelet, Yunnanozoon, lived about 530 million years ago during. Fossils of these organisms have also been found in the famous Burgess Shale of British Columbia.
• Larval chordates, or tunicates ( Urochordata) : There are currently about 1,600 species of tunicates. This subphylum is divided into classes such as ascidians and appendicularians. Tunicates are marine filter feeders, most of which do not move but rather attach to rocks or other hard surfaces on the seabed.
• (Vertebrata) - Today there are about 57,000 species of vertebrates. Members of this group include lampreys, mammals, birds, amphibians, reptiles and fish. During development, the vertebrate notochord is replaced by a vertebral column.

1. General characteristics of the type Chordata.

The phylum Chordata 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 characteristics:

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 notochord is preserved for life only in lower chordates, and in higher chordates it is replaced by a vertebral column.

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

c) The presence of gill slits in the wall of the pharynx, which in proto-aquatic animals remain throughout life, but in others 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) Deuterostome;

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, consisting of epidermis and dermis.

The phylum Chordata includes three subphyla: Tunicates, Anos-cranials (cephalochordates) and Cranials (vertebrates).

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

Cranials are a small group of primitive chordates in which all the main characteristics of the type are preserved throughout life. They live exclusively in the seas, where they lead a bottom-dwelling 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. Narrow dorsal smoothly passes into the tail, which has a lanceolate shape. At the anterior end there is an oral 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 dorsal) 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 (approximately 90 pairs). Lancelets are dioecious. External fertilization. Larval development lasts about three months. The study of the structure of skullless animals sheds light on the origin of chordates. The lancelet can be considered an intermediate form between ancient annelids and modern vertebrates.