Chordates are the most highly organized creatures of all representatives of the animal kingdom. The characteristic structural features allowed them to become the pinnacle of evolution.
Traits of chordates
The main features of these animals are the presence of a notochord, a neural tube and gill slits in the pharynx. Chordates are organisms in which the listed characteristics can vary significantly.
So, the skeleton can be external and internal. And the development of chordates in ontogenesis can be characterized by the fact that the gill slits are overgrown even in the embryonic development of organisms. At the same time, they develop other respiratory organs - air sacs or lungs.
Axial skeleton
The main characteristic of chordates is the presence of a notochord. It is internal, which in the form of a solid cord passes through the entire body. Not many representatives of this type retain the notochord throughout their lives. These include different species of lancelets, representing the class Cephalochordates of the subtype Invertebrates.
In other representatives, the notochord develops into a skeleton. Only for a few does it consist of cartilage tissue. Bony fish, birds and mammals have a completely ossified skeleton. In the process of evolution it becomes more complex. Its components are the skull, spine, chest, belts and the upper and lower limbs themselves.
Gill slits in the pharynx
Chordates are animals that develop pharynxes as outgrowths. This is their main difference from invertebrates. In this group they are derivatives of the limbs.
Of course, not all chordates have this anatomical feature. Gill slits are preserved in the lancelet and cartilaginous fish: sharks and rays. In animals that are adapted to breathing atmospheric oxygen, they become overgrown in the early stages of embryonic development. Afterwards the lungs are formed.
Features of the nervous system
A system that provides interconnection between the body and environment, in chordates it is initially formed as a neural tube. It is of ectodermal origin.
Chordates are highly developed animals, largely due to the structural features of the nervous system. Thus, in mammals it is represented by the spinal cord, located in the spinal canal, as well as the brain. They are parts of the central nervous system. The brain is reliably protected by the bones of the skull, which are fixedly connected. It is differentiated into departments based on functional characteristics. Anatomically, the brain is connected to the spinal cord through the opening formed by the vertebrae. The peripheral part of the system is formed by the spinal and cranial nerves. They act as a “transport highway,” uniting a complex organism into a single whole and coordinating its work.
Determines the complex behavior of chordates, the formation conditioned reflexes and a clear program of instinctive behavior.
Diversity of chordates
This phylum includes three larvalochordates (tunicates) and cranial (vertebrates).
The first of these includes only 30 species found in our time. Their representatives are lancelets. These animals look like a surgical instrument called a lancet.
The body of these small animals is almost always half in the sand. This makes it more convenient for the lancelet to filter water by swallowing nutrient particles.
The most numerous subphylum of chordates are Vertebrates. They have colonized absolutely all habitats, filling food chains and ecological niches.
Aquatic inhabitants are fish. Their streamlined body is covered with scales, they are adapted to gill breathing, and move with the help of fins.
The first animals to reach land were amphibians. These are frogs, toads, newts, worms and fish snakes. Their common name is due to the fact that they live on land, breathe using their lungs and skin, but the process of their reproduction occurs in water. Like fish, their females lay eggs in the water, which the males water with seminal fluid.
Typically terrestrial animals are reptiles. Lizards, snakes, turtles and crocodiles spend only time hunting in water. They reproduce by eggs, which they lay in special shelters on land. Their skin is dry and covered with dense scales.
The last trait was inherited from reptiles by birds. The unfeathered part of their legs is called the tarsus. It is she who is covered with small scales. Scientists consider this fact as evidence of origin in the process of evolution. Birds are capable of flight due to many features of their external and internal structure. These are modified forelimbs, feather cover, a light skeleton, the presence of a keel - a flat bone to which the muscles that move the wings are attached.
Finally, Beasts, or Mammals, are the crown of evolution. They are viviparous and feed their young with milk.
Chordata animals are the most complexly organized, diverse in structure, playing a vital role in nature and human life.
lecture 1: phylum chordates. general characteristics.
1. General characteristics of the type Chordata.
2. General features of the organization of chordates.
3. Chordata type system.
1. General characteristics of the type Chordata.
About 43 thousand modern species all over the globe. They are diverse and vary in size: from a few mm (appendicular) to 30 m, 150 tons (blue whale).
General features of the organization:
1) The presence of a notochord (at least in one of the phases of development) - the internal axial skeleton. Notochord of endodermal origin made of highly vacuolated cells, surrounded by a connective tissue membrane. In most vertebrates, during ontogenesis it is replaced by the vertebral column.
2) The central nervous system has the shape of a neural tube with a cavity - a neurocele. It is of ectodermal origin and lies above the notochord. In vertebrates it differentiates into the brain and spinal cord.
3) The anterior section of the digestive tube - the pharynx - is penetrated by gill slits and performs 2 functions - digestion and respiration. In aquatic chordates, gills develop on the partitions between the gill slits; in higher chordates they are present only at the embryonic stage; in the postembryonic period they are overgrown, and lungs are formed - paired outgrowths of the posterior part of the pharynx.
4) The pulsating organ of the circulatory system - the heart - is located on the ventral side of the body, under the notochord and the digestive tube.
These characters are characteristic only of chordates. However, there are other features characteristic of other animals:
1) Deuterostomes;
2) Secondocavity animals, there is a coelomic cavity;
3) Metameric animals (in higher vertebrates, metamerism is manifested in the structure of the spinal column and some muscles, the origin of spinal nerves);
4) Bilaterally symmetrical (bilateral) animals.
Chordates evolved from coelomic worm-like animals that switched to a sedentary or sedentary lifestyle, which resulted in a decrease in the number of segments and the formation of a secondary mouth.
These animals gave rise to 3 types:
1) Echinoderms;
2) Pogonophorans are simple animals with a central nervous system from the dorsal trunk with the cephalic ganglion; organs of movement and a digestive tube are absent (characteristic is extraintestinal digestion by absorption of nutrients by the cells of the tentacles);
3) Hemichordates - gave rise to 2 classes:
a) class Cirrusbranchs b) class Intestinal-breathing.
Representatives of these classes have the following characteristics of chordates:
1) The presence of gill slits in the walls of the pharynx;
2) The rudiment of the myochordal complex;
3) Neurocoel in the neural tube.
There are 2 hypotheses for the origin of chordates from hemichordates:
1) Garstang hypothesis (1928)
Chordates evolved from the larvae of gastrobreathers. Some gut-breathers switched to a sedentary lifestyle, filtering water through a pharynx perforated by gill openings. Their mobile larvae developed the ability to reproduce at the larval stage (neoteny), which led to the appearance of a mobile chordate ancestor with a developed notochord and a neural tube above it. Proof of this theory is the existence of ascidian larvae with chordate characteristics.
2) Severtsov’s hypothesis (1912, 1939)
Chordata descended from the worm-like, crawling or burrowing ancestors of the gastrobreathers, in which the notochord evolved; in the pharynx with gill slits, an endostyle appeared - an organ that secretes mucus and ensures the capture of food from filtered water.
With the transition of primitive chordates to fresh water bodies, further development motor system, intensification of metabolism and activation of food collection, consequently, the development of the nervous system and sensory organs, complication of behavior, which led to the emergence of higher chordates - vertebrates.
2. General features of the organization of chordates.
1) Musculoskeletal system:
The basis is the myochordal complex, formed by the central dorsal chord (vertebral column) and the adjacent metameric muscles. The improvement of this system led to the emergence of swimming, running, jumping, burrowing, climbing and flying animals that populated all environments.
2) Nutrition and digestion:
Differentiation of the digestive tract occurs. In lower chordates, a mucous network appears to capture food particles; in vertebrates, an apparatus for active food capture (jaws) is formed. Characteristic active search and food production. The appearance of a conveyor belt of enzymes: certain enzymes are located in different parts of the digestive tract → sequential hydrolysis of the food bolus. Outgrowths of the digestive tract appear - the liver and pancreas.
3) Breathing:
In lower and aquatic chordates, the gill apparatus is formed on the gill septa of the pharynx → the surface of contact of the capillaries of the gill apparatus with flowing water increases → rapid withdrawal of O 2 occurs. The transition to atmospheric respiration using the lungs led to the settlement of land by chordates. The blood and muscles are characterized by the presence of two respiratory pigments: hemoglobin (red blood cells) and myoglobin (red muscles).
4) Circulatory system:
Characterized by a closed circulatory system; a heart appears divided into chambers and sections; endothelial linings of the walls of blood vessels appear → regulation increases and the stability of the internal environment of the body increases, which leads to the transition from poikilothermy to homeothermy. The content of sugars in the blood plasma increases, the amount of proteins in the plasma increases → increased resistance to infections (immunity).
5) Selection:
In the series of chordates, a transition occurs from the nephridial excretory system (lancelet) to the trunk (aquatic chordates) and pelvic (terrestrial chordates) kidneys. That. kidneys are the main organ of water-salt metabolism.
6) Nervous and endocrine systems:
The central nervous system has the form of a tube; in vertebrates it is differentiated into the brain and spinal cord. The number of neuron cell bodies (gray matter) in the brain increases (more than a billion in mammals). Complex neural circuits are formed that ensure the collection, transmission and processing of the state of the body and the external environment (sense organs become more complex). The endocrine system is highly complex. There is a huge variety of hormones (thyroid, steroid, mineralcorticoid, etc.). There is neurohumoral regulation of life processes - reproduction, molting, migration, hibernation, etc.
3. Chordata type system.
Phylum Chordata
1. Subtype Tunicates, or Larval Chordates (Tunicata, seu Urochordata)
1) Class Ascidiae (Ascidiae)
2) Class Salpae
3) Class Appendiculariae
2. Subtype Skullless (Acrania)
1) Class Cephalochordata (lancelet)
3. Subtype Cranial, or Vertebrata (Craniota, seu Vertebrata)
A. Section Agnathans (Agnatha)
1) Class Cyclostomata
a) Subclass Lampreys (Petromyzones)
b) Subclass Hagfish (Myxines)
B. Section Gnathostomata
Superclass Pisces
1) Class Cartilaginous fish (Chondrichthyes)
a) Subclass Elasmobranchii (sharks and rays)
b) Subclass Holocephalii (chimeras)
2) Class Bony fish (Osteichthyes)
a) Subclass Lobe-finned (Sarcopterygii) (lobe-finned and lungfish)
b) Subclass Ray-finned (Actinopterygii) (ganoid and teleost)
Superclass Tetrapods, or Terrestrial vertebrates (Tetrapoda)
1) Class Amphibians, or Amphibians (Amphibia)
a) Subclass Thin-vertebrates (Lepospondylii) (tailed and legless)
b) Subclass Arcvertebrates (Apsidospondylii) (tailless)
Classes Bony and Cartilaginous fishes of the superclass Fishes and class Amphibians of the superclass Tetrapods belong to the morphophysiological group of proto-aquatic vertebrates, or Anamnia.
2) Class Reptiles, or Reptiles (Reptilia)
a) Subclass Anapsida (turtles)
b) Subclass Archosauria (crocodiles)
c) Subclass Lepidosauria (Lepidosauria) (beak-headed and scaly)
3) Bird Class (Aves)
a) Subclass Ancient birds (Archaeornithes)
b) Subclass True, or Fan-tailed birds (Neornites)
superorder Floating (Impennes) (penguin-like)
superorder Runners (Ratita) (ostrich-like)
superorder Keeleds, or New Palates (Neognathae) (about 30 orders)
4) Class Mammals (Mammalia)
a) Subclass of the First Beast (Prototheria)
infraclass Atheria (monotreme, or cloacal)
b) Subclass Real beasts (Theria)
infraclass Lower animals (Metatheria) (marsupials)
infraclass Higher animals, or Placentals (Eutheria, seu Placentalia)
The classes Reptiles, Birds and Mammals of the superclass Tetrapods belong to the morphophysiological group of primary terrestrial vertebrates, or amniotes (Amniota).
Chordates include about 40 thousand various types individuals that differ from others in structure, lifestyle, and habitat.
The Paleozoic era contributed to the emergence of this type of animal approximately 500 million years ago. Scientists suggest that their ancestors were annelids.
Chordates settled throughout the planet and became habitual inhabitants of the sea, land, air and even soil.
What is a chord and who are chordates?
Internal structure chordates are different from others. They are characterized by the presence of an axial skeleton - the vertebral column, which is otherwise called the notochord.
It was this feature of the structure of the spine that gave the name to chordates.
Structural features
The following features are characteristic of chordates:
- The location of the neural tube above the axial skeleton and the formation of the spinal cord from it.
- The presence of a rod - a chord.
- Absence of intestines in the caudal region.
- Location of the heart under the digestive tract.
Phylum Chordata (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 of development historical world animals.
The emergence of this type meant the emergence of new animals with a unique structure, which allowed them to further evolve into 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, the evolution of annelids, or, as they are also called, benthic worm-like animals, gave birth to new types: echinoderms, pogonophorans, hemichordates and chordates.
Subsequently, chordates evolved in three directions, depending on their lifestyle:
- 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 over the entire surface of the body. These individuals have the ability to reproduce asexually. This is how tunicates appeared.
- The habitat of individuals of the second direction is the bottom. They moved a little more, digging into the ground. This lifestyle simplified their original organization. The development of the myochordal complex required increased mobility, and the growth of the pharynx added new gill slits. This branch has survived to this day in the form of the skullless.
- 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 and increased mobility. The nervous system and sensory organs became more sophisticated, which led to more complex behavior and the emergence of more complex forms. This is how 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 to salt water and became the progenitors of modern groups of fish.
Later, amphibians separated from fish. Then they came to land, and thus a new species appeared - reptiles.
General characteristics of the type Chordata
The cover consists of two layers of leather. The top layer is represented by the epidermis and its derivatives: scales, feathers, wool, hair. This layer of skin contains scent glands that produce mucus and sweat. The bottom layer is the dermis, consisting of fibrous connective tissue.
The musculoskeletal system is presented in the form of a skeleton, consisting of a chord and connecting tissues of the membrane. The skeleton of the head is divided into the brain and facial parts.
Fish develop jaws, and vertebrates develop two pairs of limbs. Bones are connected by joints.
The respiratory system in lower chordates is represented by gills, and in vertebrates by lungs. In addition, the skin of chordates is partially involved in gas exchange.
The digestive system of cephalochordates is a straight tube and almost undeveloped digestive glands. In vertebrates, this is the digestive canal, which has sections.
Food first enters the oral cavity, then passes into the pharynx, begins to be processed in the esophagus, passes into the stomach, and finally enters the intestines. In addition to the listed organs, vertebrates have a liver and pancreas.
The circulatory system is closed. In vertebrates, due to an increase in metabolic rate, the heart appeared and became more complex. Cephalochordates do not have a 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 includes the cranial and spinal nerves that arise from the central nervous system.
The excretory system of all chordates, except lancelets, is represented by paired kidneys, ureters and a bladder.
Reproductive system: reproduction occurs using testes in males and ovaries in females. Tunicates are hermaphrodites; they reproduce sexually and asexually. Other chordates have 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:
- skullless;
- tunicates;
- jawless;
- primary: classes of fish;
- tetrapods: classes of amphibians or amphibians, reptiles or reptiles, birds, mammals.
What characteristics of chordates does a person have?
In humans, like chordates, in the early stages of development, the formation of the axial skeleton, i.e., the notochord, occurs. The musculoskeletal system in humans is represented, as in vertebrates, by the supporting internal skeleton.
Humans also have the following characteristics of chordates:
- central nervous system, which has a tubular structure;
- a closed circulatory system with the main circulatory organ - the heart;
- a breathing apparatus capable of communicating with the external environment through the pharynx, nasal cavity and mouth.
Monkey eel
Some interesting information:
The importance of chordates is very great; they are classified among the most diverse and numerous types. On this moment There are about 50 thousand species of chordates. The presence of a common feature in all individuals - the notochord (supporting organ) - gave the name to this type of animal.
The anatomical features of chordates are similar to echinoderms. The lowest representatives of chordates are lancelets, which retain their main character throughout their lives.
1.General characteristics of the type Chordata The phylum Chordata unites animals that are very diverse in appearance, lifestyle and living conditions. Representatives of chordates are found in all major environments of life: in water, on the land surface, in the soil and, finally, in the air. Geographically, they are distributed throughout the globe. Total number The number of species of modern chordates is approximately 40 thousand. The phylum Chordata includes skullless (lancelets), cyclostomes (lamreys and hagfish), fish, amphibians, reptiles, birds and mammals.
2. The main characters of the chordate type. Despite the enormous diversity, all representatives of the phylum Chordata are characterized by common features organizations that are not found among representatives of other types. Let's look at the main characteristics of the type using an interactive diagram: The body is bilateral - symmetrical. The intestine is through. Above the intestines is the notochord. Above the chord, on the dorsal side of the body, the nervous system is located in the form of a neural tube. The walls of the pharynx have gill slits. The circulatory system is closed. The heart is on the ventral side of the body, under the alimentary canal. They live in all living environments.
3. General taxonomy of the phylum Chordata. Of the four subtypes of chordates - Hemichordata Hemichordata, Larval-Chordate Urochordata, Crania Acrania and Vertebrata Vertebrata - we will focus on the last two, related to the progressive direction in the evolution of this type of animal. The subphylum Cephalochordata consists of only one class - Cephalochordata, which includes the lancelet; The subphylum Vertebrates includes the following classes: Cyclostomata, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammalia.
4. Origin of the phylum Chordates. 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 bottom-dwelling sea sessile organisms - ascidians), skullless (small fish-like sea creatures - lancelets), vertebrates (cartilaginous and bony fish, amphibians, reptiles, birds and mammals). Man is also a representative of the chordate phylum. The origin of the chordate phylum is the most important stage in the historical development of the animal world, meaning the appearance of a group of animals with unique plan building, which allowed further evolution to achieve the maximum complexity of structure and behavior among living beings.
5.General characteristics of the subtype Tunicates.Tunicates, or Larval chordates(lat. Tunicata, Urochordata) - a subphylum of chordates. Includes 5 classes - ascidian, appendicularian, salp, fire beetle and columbine. According to another classification, the last 3 classes are considered class units Thaliacea. More than 1000 species are known. They are common in seas around the world. The body is sac-shaped, surrounded by a shell or mantle ( Tunica listen)) from tunicin, a material similar to cellulose. The type of feeding is filtering: they have two openings (siphons), one for sucking in water and plankton (oral siphon), the other for releasing it (cloacal siphon). The circulatory system is not closed; a notable feature of tunicates is the regular change in the direction in which the heart pumps blood.
6.Organization of Ascidians as typical representatives of tunicates. Ascidians are bottom-dwelling animals that lead an attached lifestyle. Many of them are single forms. Their body sizes on average are several centimeters in diameter and the same in height. However, among them some species are known 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, measuring less than 1 mm. The digestive canal of ascidians begins with the mouth, located at the free end of the body on the introductory, or oral, siphon.
8. General characteristics of the Cheskull subtype. Skullless- marine, mainly bottom-dwelling animals that retain the basic characteristics of the Chordata type throughout their lives. Their organization represents, as it were, a diagram of the structure of a chordate animal: they function as an axial skeleton 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 it remains metamerism. Characteristic of skullless animals bilateral (bilateral) symmetry bodies. These characters indicate a phylogenetic connection between skullless animals and certain groups of invertebrate animals (annelides, echinoderms, etc.).
9.External and internal structures of the lancelet as a representative of the skullless subtype . Lancelet (Amphioxus lanceolatus This small animal (6–8 cm long) lives in shallow seas, burrowing into the bottom soil and exposing the anterior part of its body. Cranials, 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 epithelium (epidermis) and covered with a thin cuticle. The central nervous system is not differentiated into the brain and spinal cord. Due to the absence 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 - Hessian eyes located in the walls of the neural tube. The gill slits do not open outward, but into the atrial, or peribranchial, cavity, which arises as a result of the fusion of the lateral (metapleural) folds of the skin. The digestive system consists of a poorly differentiated tube, in which only two sections are distinguished - throat and gut. The lancelet's blood is colorless and there is no heart. The reproductive organs - testes and ovaries - are similar in external structure and are round bodies.
11. General characteristics subphylum Vertebrates. External features of the structure. The cranial subphylum includes all known vertebrates, whose probable evolutionary relationships are shown in. existence on land. Thus, reptiles are the first completely terrestrial vertebrates. Zoologists sometimes use the collective term amniotes for all fully terrestrial vertebrates (reptiles, birds and mammals), in contrast to anamnia (amphibians and fish), which lack an amniotic membrane and are therefore necessarily part life cycle or the whole thing is forced to spend in water. The highest subphylum of the chordate phylum, whose representatives have a bony or cartilaginous internal skeleton. Divided into superclasses fishes (jawless, cartilaginous fishes and bony fishes) and tetrapods (amphibians, reptiles, birds and mammals). The vertebrate subphylum includes the following classes: fish, amphibians, reptiles, birds and mammals.
13.Primitive, peculiar and specialized characters of the class Cyclostomes. The only representatives of jawless animals that have survived to this day - lampreys (Petromyzones) and hagfish (Myxini) - constitute the class of cyclostomes (Cyclostomata), the most ancient of modern vertebrates. In contrast to 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. There are no real teeth; instead, the oral funnel is armed with horny teeth. Cyclostomes do not have paired limbs. The nasal opening is single, unpaired, since the olfactory organs are combined into one nasopituitary sac. The visceral skeleton has the appearance of an openwork lattice and is not divided into separate articulated 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 Agnathans. (up to representatives). Jawless(lat. Agnatha listen)) is an archaic group (superclass or clade) of craniate chordates, almost completely extinct in modern times, with the exception of 39 species of lampreys and 76 species of hagfish. Jawless animals are characterized by the absence of jaws, but they have a developed skull, which distinguishes them from skullless animals. Hagfishes and lampreys were traditionally considered a monophyletic group and were united under the name Cyclostomata. But there is an alternative hypothesis, according to which minogyphylogenetically is closer to gnathostomes than to hagfishes.
16. General characteristics of the class Cartilaginous fish in connection with an active lifestyle. CLASS CARTILIATED FISHES (CHONDRICHTHYES). Cartilaginous fishes arose in the Upper Silurian from jawless fishes, which switched to faster, longer swimming and more successful capture of prey with mouths armed with jaws. 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 fishes. Currently, there is only one small group of predatory cartilaginous fish called elasmobranchs. They are widespread in the seas. Elasmobranchs include sharks - excellent swimmers - and rays, which lead a sedentary lifestyle on the bottom. There are about 350 species of sharks, about 340 species of rays. 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 fish. class of cartilaginous fish (lat Chondrichthyes). It is one of two existing classes of fish. The class Cartilaginous fishes are divided into the subclass Elasmobranchii or Elasmobranchs and the subclass Holocephali or Whole-headed fishes. The best known members of this class are Selachii or sharks and Batoidea or rays. Both of them belong to the subclass Elasmobranchs.
20. Primitive featuresstructure of organ systems of cartilaginous fish. All cartilaginous fish are characterized by the following primitive features: the skin is either covered with placoid scales or naked (in chimeras and some stingrays), gill slits open outward, like in lampreys, and only chimeras have skin membranes covering the gill slits. The skeleton has no bones and is formed exclusively by cartilage (which, however, is often impregnated with lime), the unpaired fins and the distal part of the paired fins are supported by elastin (“horny”) rays, there are wide interbranchial septa, usually reaching the surface of the body, there is no swim bladder, no lungs.
18. External structure of the shark as the first jawed vertebrates. Sharks(lat. Selachii) - above the order of cartilaginous fish (Chondrichthyes), belonging to the subclass of elasmobranchii (Elasmobranchii) and having the following distinctive features: an elongated body more or less torpedo-shaped, 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 existed already about 420-450 million years ago. To date, more than 450 species of sharks are known: from the deep-sea small Etmopterus perryi, only 17 centimeters long, to the whale shark (Rhincodon typus) - the largest fish (its length reaches 20 meters). Representatives of this order are widely distributed in the seas and oceans, from the surface to depths of more than 2000 meters. Mainly live in sea water, but some species are also able to live in fresh water. Most sharks are so-called true predators, but 3 species - whale, basking and largemouth sharks - are filter feeders; they feed on plankton, squid and small fish.
19. Progressive features of the structure of organ systems of cartilaginous fish. These most primitive fish include sharks, rays and peculiar chimeras that inhabit seas and oceans everywhere. Some live in fresh water bodies. Along with very ancient organizational features, modern cartilaginous fish have a highly developed nervous system and sensory organs and a very advanced reproduction biology. Characteristic features also include the following progressive organizational features that bony fish do not have: the brain has very highly developed (for fish) anterior hemispheres brain, males have peculiar copulatory organs, representing modified parts of the pelvic fins, internal insemination, and females either lay large eggs covered with a dense horn-like membrane, or give birth to live young, the development of which occurs in the “uterus”.
21. Taxonomy of the class Bony fish. Bony fish(lat. Osteichthyes) - 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 internal skeletal support, and 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 directly into the intestines. Partial digestion of food occurs in the stomach under the influence of gastric juice. Final digestion of food occurs in the small intestine. The duct of the gallbladder, liver and pancreatic duct flow into the initial part of the small intestine. In the small intestine nutrients are absorbed into the blood, and undigested food remains are removed through the anus. Breathing through the gills. From the oral cavity, water passes through the gill slits, washes the gills and comes out from under the gill covers. The gills consist of gill arches, which in turn consist of gill filaments and gill rakers. The circulatory system of fish is closed; the heart consists of 2 chambers: the atrium and the ventricle. A large blood vessel, the aorta, branches off into smaller ones, the arteries, from the ventricle to the gills. In the gills, the arteries form a dense network of tiny vessels - capillaries. Substances that are unnecessary for the body are released from the blood when they pass through the excretory organs - the kidneys. Two ureters extend from the kidneys, through which urine flows into the bladder and is removed out through the opening behind the anus. In most species, fertilization is external. In species with internal fertilization, the male copulatory organ is formed by a modified part of the anal fin.
22. Features of the progressive organization of the class Bony fish. In bony fish, cartilage in the skeleton is replaced to one degree or another by bone tissue: main or replacement bones are formed. In addition, integumentary bones appear in the skin, which then sink under the skin and form part of the internal skeleton. The skeleton of bony fishes is divided 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 the organ systems of bony fish, as progressive aquatic vertebrates. They have scales of ganoid, cycloid or ctenoid type. The skeleton is bony. The internal cavity of bony fish contains the organs of digestion, circulation, excretion and reproduction. The complex of progressive structural features of bony fishes is especially clearly and fully expressed in the youngest and most progressive branch of this class - the bony fishes Teleostei, which includes the vast majority of living forms of this class.
26.Subclass Ray-finned fishes as the main group of the bony fish class, its characteristics. Ray-finned fish(lat. Actinopterygii) - a class of fish from the superclass of bony fishes. 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 the many-kilometer depths of the ocean and salt lakes to streams and underground springs. Fish scales are ganoid or bony. In some, the scales merge to form bone plates, while in others the skin is bare. A well-developed notochord is preserved only in a few species; fish usually have bony vertebrae. Ray-finned fish have a developed swim bladder; 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 four-legged animals, including, among others, newts, salamanders, frogs and caecilians - in total more than 6,700 (according to other sources - about 5,000) modern species, which makes this class relatively small. 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, and adult individuals live on land. All amphibians have smooth, thin skin that is relatively easily permeable to liquids and gases. The structure of the skin is characteristic of vertebrates: there is a multi-layered epidermis and the skin itself (corium). The skin is rich in cutaneous glands that secrete mucus. For some, mucus may be toxic or facilitate gas exchange. The skin is an additional organ of gas exchange and is equipped with a dense network of capillaries. Horny formations are very rare, and ossifications of the skin are also rare: Ephippiger aurantiacus and the horned toad of the species Ceratophrys dorsata have a bony plate in the skin of the back, while legless amphibians have scales; Toads sometimes develop lime deposits in their skin when they get old.
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, first of all, 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 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. Taxonomy of the Amphibian class. Amphibians are the smallest class of vertebrates, comprising only about 2,100 living 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 the number of species. The most numerous are tailless amphibians (Ecaudata, or Anura), which have adapted to move on land by jumping with the help of elongated hind limbs (hence their name jumping - Salientia) and are distributed across all continents. More primitive are the tailed amphibians (Caudata, or Urodela), typical representatives of which are newts and salamanders, which are much less common and distributed almost exclusively in the northern hemisphere (about 280 species). Finally, the third, smallest order of legless (Apoda) contains only tropical caecilians, which are, apparently, the remains of very ancient armored amphibians that have survived to this day due to specialization for a burrowing lifestyle (about 55 species).
28. Features of the class Amphibians as animals leading a dual lifestyle. Most amphibians spend their lives in damp places, alternating between being on land and in water, but there are some that are purely aquatic species, as well as species that live exclusively in trees. The insufficient adaptability of amphibians to live in the terrestrial environment causes sudden changes in their lifestyle due to seasonal changes in living conditions. Amphibians are capable of hibernating for a long time under unfavorable conditions (cold, drought, etc.). In some species, activity may 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 torpor, and at −1 °C they die. But some amphibians are able to withstand 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 generally favorable for them, 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 infraorbital openings (windows), thecodont teeth that do not have roots and are formed in separate cells (alveoli). The subclass of archosaurs is divided into four superorders: thecodonts, dinosaurs, pterosaurs and crocodiles. Archosaurs appeared in the Permian and existed until today. Thecodonts existed from the Late Permian to the Triassic, dinosaurs from the Middle Triassic to the Cretaceous, pterosaurs from the Late Triassic to the Cretaceous, crocodiles from the Late Triassic to the present day.
31. General characteristics and taxonomy of the subclass Arcuvertebrate amphibians. The first subclass of arcvertebrates (Apsidospondyli) contains 4 orders bearing the general name of the superorder labyrinthodontia (Labyrinthodontia). The most ancient order of Devonian stegocephalians - ichthyostegans (Ichtyostegalia) - preserved the remains of the gill cover of fish. Labyrinthodonts include the order of embolomeric stegocephalians (Embolomeri), widespread in the Carboniferous period, Permian rachitoms (Rachitomi) and stereospondylic stegocephalians (Stereospondyli4o), which separated from them in the Triassic. This entire group of labyrinthodonts disappeared at the boundary of the Jurassic period.
32. External structure of a frog as a representative of the amphibian class. The pond frog has a short and wide body, gradually turning into a flat head. The neck is not expressed. The tail is missing. The nostrils are located above the large mouth, and above them there are bulging eyes. There are valves in the nostrils that block the entry of water into 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 dismembered limbs. The hind limbs are the most developed. With their help, the frog moves by jumping on land and swims well. There is a swimming membrane between the toes of the hind limbs.
33. Features of the internal structure of the frog as a representative of the amphibian class. The skeleton of amphibians consists of the same main sections as the skeleton of fish. It is based on the skull, spine, bones of the free limbs and their girdles. Unlike fish, the frog's skull is movably articulated with the spine, and the ribs are not developed. Main distinctive features in the structure of the skeleton are associated with the access of amphibians to land and with movement on a hard surface with the help of free limbs - the front and hind legs. The skeleton of the fore and hind limbs is supported by the bones of their girdles. The skeleton of the forelimb consists of the humerus, the bones of the forearm and the hand. The skeleton of the hind limb contains the femur, 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 of a frog is also more complex than that of a fish. In connection with movement on land, amphibians develop the muscles of the free limbs, especially the hind limbs.
34.Structural features of amphibians that arose as adaptations to 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, damp forests, meadows, along the banks of freshwater bodies or in water. Mostly adult individuals are found on land, 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 it sets or in wet, rainy weather, it is time for them to hunt. Other species live in the water or near the water, 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 grass frog overwinters at the bottom of non-freezing reservoirs, in the upper reaches of rivers and streams, accumulating in tens and hundreds of individuals, freezing together with the water, and with the onset of warmth they begin an active lifestyle.
35 . Reptiles, as the first class of true terrestrial vertebrates. Class REPTILES OR REPTILES (Reptilia) Reptiles, compared to 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 the suction type (by changing the volume of the chest), well-developed conducting respiratory tracts, 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 the 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 girdles of the limbs are strengthened, the spine is divided into cervical, thoracic, lumbar, sacral and caudal sections, and the mobility of the head increases. The skull of reptiles, like that of birds, unlike other vertebrates, is connected to the spine by one (unpaired) condyle. The skeleton of the free limbs is characterized by intercarpal (intercarpal) and intertarsal (intertarsal) joints. In the girdle of the forelimbs they have a kind of integumentary bone called the episternum. There are now about 7,000 species of reptiles, almost three times as many as modern amphibians. Living reptiles are divided into 4 orders: Scaly; Turtles; Crocodiles; Beaked.
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 dense parchment-like shell. Fertilization only internal. Embryonic development goes in the air with the formation of embryonic membranes - amnion and serosa - and allantois; there is no larval stage. A young animal hatched from an egg differs from adults only sizes.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 pulmonary. Airways are formed - the trachea and bronchi. Breathing is carried out by movements of the chest. Heart three-chamber. Three blood trunks independently branch off from the ventricle, divided by an incomplete septum: two aortic arches and the pulmonary artery. The carotid arteries supplying the head arise only from the right aortic arch. The systemic and pulmonary circulations are not completely separated, but the degree of their separation is higher than in amphibians. Selection and water metabolism are ensured by the metanephric (pelvic) kidneys. The relative sizes of the head increase brain, especially due to the enlargement of the hemispheres and cerebellum. Skeleton completely ossifies. The axial skeleton is divided into five sections. Elongation of the neck and specialized first two cervical vertebrae (atlas and epistrophy) provide high mobility of the head. Scull has one occipital condyle and well-developed integumentary bones; Characterized by the formation of temporal pits and the bony temporal arches that limit them. Limbs terrestrial 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 mainly in warm, partly in temperate latitudes; some species again switched to water way of life.
30. General characteristics and taxonomy of the subclass Tonkovertebrata. The second subclass of amphibians - thin-vertebrates, or lepospondyli (Lepospondyli) - unites several groups of mostly small stegocephalians (Microsauria), very numerous in the Carboniferous, but already extinct in the Permian period. Recently, lepospondylic stegocephalians have been considered the ancestral group for two modern orders of amphibians: the caudates (Caudata, or Urodela) and the legless (Apoda). However, there is no direct connection between them, since fossil remains of modern orders were found only in the Cretaceous period, and lepospondyles became extinct already in the Permian.
37 . Systematics and features of the subclass Anapsida. Anapsids (lat. Anapsida) are amniotes whose skulls do not have temporal fenestrae. Traditionally, anapsids have been considered as a monophyletic taxon of reptiles, but it has been hypothesized that some groups of reptiles with anapsid skulls may be only distantly related to each other. Many modern paleontologists believe that turtles evolved from diapsid reptiles that lost openings in their cheek bones, although this hypothesis is not shared by everyone. Of the modern anapsids, the only living representatives are turtles. Turtles were first recorded in the Upper Triassic, but 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 millerettids, nyctifrurets, and pareiasaurs, became extinct in the late Permian period in a mass extinction event.
39. Systematics and features of the subclass Scaly. Scaly(lat. Squamata) - one of four modern orders of reptiles, including snakes, lizards, and the lesser-known amphisbaenus, or two-year-old. Animals of this order are widespread in all parts of the world on continents and islands, and are absent in the polar and subpolar regions. The body is covered on top with horny scales, scutes or grains. The quadrate bone is usually movably articulated with the skull. Of the temporal arches, only the upper one is preserved, or even it is missing. The pterygoids do not articulate with the vomer. A transverse bone is usually present. The teeth are attached to the upper or inner surface jaws. The vertebrae are amphicoelous or procoelous. There are two or three sacral vertebrae, if they are pronounced. Ribs with one head. Ventral ribs are absent or vestigial. The pineal opening is present or absent.
40. External structure of a lizard. Signs associated with land development. The lizard's body is divided into sections: head, torso, tail, 2 pairs of limbs. The body is covered with dense dry skin with horny scales (there is molting). The head is oval in shape with large horny scutes. On the head there are sensory 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 and 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, fingers with claws. When moving, lizards reptile - they touch the ground with their bodies.
41. The structure of the circulatory digestive, respiratory and excretory systems of the lizard.Circulatory system of reptiles. Like amphibians, reptiles have two circulations and a three-chambered heart. But unlike amphibians, in the ventricle of the heart of reptiles there is a septum that divides it into two parts. One of them receives venous blood, and the other - arterial blood. Respiratory system reptiles consists of the lungs and respiratory tract. The lungs are formed by a large number of cells, so they have a large gas exchange surface. Through the respiratory tract - the nasal openings, larynx, trachea, bronchi - air enters the lungs. Digestive system in reptiles (Fig. 39.6) is almost the same as that of amphibians. However, not only the substances of the digestive glands, but also beneficial symbiont bacteria participate in the digestion of food in a lizard. They live in a small extension of the intestine - the cecum. Excretory system reptiles consists of kidneys, ureters and bladder connected to the cloaca.
42.Structure of the skeleton, nervous system and sensory organs of a lizard. The skeleton of a lizard consists of the same sections as those of amphibians. But in the spine of reptiles there are five sections: cervical, thoracic, lumbar, sacral and caudal. The first vertebra of the cervical spine 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 (of 5 sections) 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. They often 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 the internal nostrils - choanae and the 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 located under the surface of the sand at a depth of 6-8 cm. The organ of taste is taste buds, located mainly in the pharynx. The thermal sensory organ is located on the facial fossa between the eye and nose on each side of the head. Especially developed in snakes.
43. 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 testis a seminal canal emerges, which flows into the Wolffian canal. With the appearance of the trunk bud in wolf reptiles, the canal in males acts only as a vas deferens and is completely absent in females. The Wolffian canal opens into the cloaca, forming the seminal vesicle. Reptiles reproduce on land. Crocodiles, sea snakes and turtles, who lead a mainly aquatic lifestyle, are no exception. Fertilization in reptiles is internal. Most species experience increased activity during the breeding season: male fights are common. The amnion, as an important embryonic adaptation to development in conditions of terrestrial life, is formed not only in reptiles, but also in other higher vertebrates in the embryos of birds and mammals. Based on the presence or absence of this embryonic organ, all vertebrates can be divided into two groups - amniotes (Amniota - reptiles, birds and mammals) and anamnia (Anamnia), that is, those without an 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 their bodies. This is a streamlined “drop-shaped” body shape, and forelimbs in the form of wings, and a body cover made of feathers, and powerful muscles on the chest that ensure flight. The purpose of flight is served by the thin-walled and pneumatic nature 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 excretory products inside the body. With the acquisition of the ability of flight by birds, all evolution proceeded in close connection with this ability of theirs. Paleontological materials show that the ancestors of birds were primitive archaeosaurs who lived in the Triassic or even in the Permian period. The ancestors of birds were terrestrial running reptiles and, apparently, small 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 their structure, in the main features of organization all birds are very homogeneous. In this respect, birds are the direct opposite of reptiles. This is explained by the fact that reptiles are an ancient, almost extinct class, the main modern groups of which managed to diverge far in the process of evolution, while birds are the youngest class of vertebrates, which immediately flourished in modern era history of the Earth. The class of birds is divided into two subclasses: lizard-tailed and fan-tailed.
47. General characteristics and features of the 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 life processes, and, on the other, 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 taxonomy of the superorder Keelebreasts.Predatory(lat. Carnivora- "carnivores") - detachment (Pinnipedia).
50. External structure of a pigeon. Features of the feather cover . Feather cover is inherent only to birds, which is why they are sometimes called birds. The close-fitting plumage gives the bird a streamlined body. The feather cover, light and warm, serves as a good thermal insulator, promotes incubation of eggs, and individual feathers (flight and tail feathers) provide the ability to fly. In the vast majority of birds, the 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 pigeon is divided into the same sections as those of reptiles - head, neck,torso And limbs. The pigeon's head is small, round in shape, with a rather long and thin protrusion extended forward. beak, dressed in a horny sheath. The beak consists of two parts: the upper - upper beaks and lower - mandible. The beaks open at the base nostrils. On the sides of the head there are round eyes, somewhat lower and back from them are hidden under the feathers 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 to clean the feathers of its belly, wings, back and tail with its beak. The forelimbs are wings used for flight: their planes support the bird in the air.
51. Internal structure of a pigeon as a flying vertebrate. Features in organ systems. The internal structure of a pigeon is the same as that of other birds. It consists of: the digestive, respiratory and excretory systems. The following are also present: the 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- gastric juice is released, under the influence of which the food softens. Second department - muscular– has thick walls, food is ground in it. The jaw bones are covered on the outside with horny sheaths that form the beak. The beak varies 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 stretched.
52. Characteristics 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 high level development of the nervous system, primarily the brain. Most mammals have a constant high body temperature. Hair style usually helps retain heat. In almost all mammals, the embryo develops in the womb of the mother, who gives birth to live young. All mammals feed their young with milk, which is produced by the mother's mammary glands (hence the name of the class mammals). The combination of many progressive features determined a high level of general organization and allowed mammals to spread widely across the Earth. Among them, terrestrial species predominate. In addition, there are flying, semi-aquatic, aquatic and soil inhabitants.
53. The main features of the class mammals. Features of reproduction. The reproduction of mammals differs significantly from that of other vertebrates. Great amount animals viviparous. The viviparity observed in some reptiles, amphibians and even fish differs significantly from the viviparity of mammals. Hair, intrauterine development of the embryo, milk feeding, caring 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, very different in volume. The subclass of the first beast (Prototheria), containing only the platypus, the echidna and the closely related echidna, includes very primitive animals that reproduce by laying eggs: they 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 subclass marsupials (Metatheria) is a relatively small group, its representatives already have a separate anus and give birth to young, but they appear underdeveloped and are carried by the mother in a pouch (hence the name of the subclass). Marsupials have also survived to this day only in Australia and South America, the fauna of which, in terms of its antiquity, ranks next after that of Australia. Finally, the subclass higher, or placental (Eutheria), includes the vast majority of mammals. They are characterized by the fact that the embryo is equipped with a special organ - the placenta, through which it communicates with the mother’s body, and the babies are born more or less well developed. The brain of placentals has a significantly higher development.
First beasts are a small group of species common in the Australian region. According to a number of characteristics, the subclass of proto-beasts and the infraclass cloacae are considered the most archaic and primitive among the infraclasses of mammals. infraclass ( Zaglossus)Barton's echidna ( Zaglossus bartoni)Bruin's echidna ( Zaglossus bruijni)attenborough echidna ( Zaglossus attenboroughi)Zaglossus hacketti Zaglossus robustus family family Steropodontidae.
56. General characteristics, characteristic features and distribution of Marsupials. Taxonomy. Marsupials (Marsupialia) - an order of viviparous mammals, includes 15–16 families: opossums, predatory marsupials, marsupial anteaters, bandicoots, marsupial moles, climbing marsupials, caenolests, wombats, jumping marsupials (kangaroos), unites more than 250 species. Marsupials have been known in North America since the Lower Cretaceous, apparently descending from pantotheriums. They existed in Europe from the Eocene to the Miocene and were replaced by placental animals. Marsupials are today divided into two superorders with 7 modern orders. Superorder (Marsupialia). A distinctive feature of placentals is birth in a relatively developed 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. External structure of mammals, using the example of a representative. The body of mammals has the same sections as other terrestrial vertebrates: head, neck, torso, tail and two pairs of limbs. The limbs have sections typical of vertebrates: shoulder (thigh), forearm (lower leg) 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 of using limbs. Among the animals, tree-climbing, plantigrade and digitally walking animals, jumping and flying are known.
59. Progressive features of the internal structure of mammals, system by system. Internal structure of insects- this is a set of features of the structure and location of organs that distinguish representatives of this class from other living organisms. The organs of insects are located in the body cavity - its internal space, which is divided by level into three sections, or sinuses. This separation is possible due to the presence of horizontal partitions (diaphragms) in the cavity. The upper or dorsal diaphragm delimits the pericardial region, within which the spinal vessel (heart and aorta) is located. The inferior 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 fat body structures lie. Elements of the respiratory system are found in all three sections.
The phylum Chordata unites animals that are very diverse in appearance, lifestyle and living conditions. Representatives of chordates are found in all major environments of life: in water, on the land surface, in the soil and, finally, in the air. Geographically, they are distributed throughout the globe. The total number of species of modern chordates is approximately 40 thousand. The phylum Chordata includes skullless (lancelets), cyclostomes (lamreys and hagfish), fish, amphibians, reptiles, birds and mammals.
The chordates, as shown by the brilliant research of A. O. Kovalevsky, also include a unique group of marine, largely sessile, animals - tunicates (appendiculars, ascidians, salps). Some signs of similarity with chordates are revealed by a small group of marine animals - enteropneusta, which are sometimes also included in the phylum of chordates.
Despite the exceptional diversity of chordates, they all have a number of common structural and developmental features. The main ones are:
1. All chordates have an axial skeleton, which initially appears in the form of a dorsal string, or notochord. The notochord is an elastic, non-segmented cord that embryonically develops by detaching it from the dorsal wall of the embryonic intestine: the notochord is of endodermal origin. The subsequent fate of the chord is different. It is preserved for life only in lower chordates (with the exception of ascidians and salps). In most representatives, the notochord is reduced to one degree or another due to the development of the spinal column. In higher chordates it is an embryonic organ and in adult animals it is to one degree or another replaced by vertebrae; in connection with this, the axial skeleton from a continuous unsegmented cord becomes segmented. The spine, like all other skeletal formations (except for the notochord), is of mesodermal origin and is formed from a connective tissue sheath surrounding the notochord and neural tube.
2. Above the axial skeleton is the central nervous system of chordates, represented by a hollow tube. The cavity of the neural tube is called 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 part of the neural tube grows and forms the brain. The internal cavity is preserved in this case in the form of the ventricles of the brain. Embryonic, the neural tube develops from the dorsal part of the ectodermal primordium.
3. The anterior (pharyngeal) section of the digestive tube communicates with the external environment by two rows of openings, called visceral slits. In lower forms, gills are located on their walls. Gill slits are preserved for life only in lower aquatic chordates. In others, they appear only as embryonic formations, functioning at some stages of development or not functioning at all.
Along with the above three main characteristics of chordates, the following should be mentioned character traits their organizations, which, however, in addition to chordates, are also found in representatives of some other groups. Chordates, as well as