Type characteristics and system. The phylum chordata is often called the highest phylum of animals. This is not entirely accurate, since chordates crown only the branch of deuterostomes ( Deuterostomia), while the top of the protostome branch ( Protostomia) are occupied by types: arthropods ( Arthropoda) and shellfish ( Mollusca). The development of both branches followed different paths and led to the development of fundamentally different, but biologically highly active and complex types of organization of living matter.
Existence of type Chordata was substantiated by the famous Russian zoologist A. O. Kovalevsky, who, while studying the development (ontogenesis) of tunicates ( Tunicata) and skullless ( Acrania), established the fundamental similarity of their organization with vertebrates. The name of the type chordate was proposed by Ball in 1878. Now the type chordate is accepted in the following volume (extinct groups are marked with a cross (†).
The subphyla anesculates and tunicates are usually called lower chordates, contrasting them with higher chordates - the subphylum vertebrates.
About 43 thousand belong to the chordata phylum. modern species, distributed throughout the globe: they inhabit seas and oceans, rivers and lakes, continents and islands. The external appearance of chordates is very diverse (stationary sac-like ascidians, somewhat worm-like skullless, vertebrates of various appearances). The sizes are also different: from appendiculars a few millimeters long, small fish and frogs 2-3 cm long, to giants - some whales, reaching 30 m in length and weighing up to 150 tons.
Despite the enormous diversity, all representatives of the chordate type are characterized by common organizational features that are not found in representatives of other types:
1. The presence throughout life or at one of the phases of development of the dorsal string - chord (chorda dorsalis), which plays the role of the internal axial skeleton. It is of eitodermal origin and represents an elastic rod formed by highly vacuolated cells; the notochord is surrounded by a connective tissue membrane. In most vertebrates, during individual development (ontogenesis), the notochord is replaced (displaced) by the spinal column, consisting of individual vertebrae; the latter are formed in the connective tissue membrane of the chord.
2. Central nervous system has the shape of a tube, the internal cavity of which is called a neurocele. The neural tube is of ectodermal origin and lies above the notochord. In vertebrates, it is clearly differentiated into two sections: the brain and the spinal cord.
3. The anterior section of the digestive tube - the pharynx - is lined with gill openings that open outward and performs two functions: a section of the digestive tract and a respiratory organ. In aquatic vertebrates, specialized respiratory organs—gills—develop on the partitions between the gill slits. In terrestrial vertebrates, gill slits are formed in the embryo, but soon become overgrown; specific organs of air respiration - the lungs - develop as paired protrusions on the ventral side of the back of the pharynx. The digestive tract lies under the notochord.
4. The pulsating section of the circulatory system - the heart - is located on the ventral side of the body, under the notochord and the digestive tube.
In addition to these typical characteristics, chordates are characterized by some features that are also found in other types.
1. By breaking through the gastrula wall, a secondary mouth is formed; in the area of the primary mouth (gastropore), an anal opening is formed. This character unites chordates with hemichordates, echinoderms, chaetognaths and pogonophora into the group of deuterostomes - Deuterostomia, opposed to the group of protostomes - Protostomia, in which a mouth opening is formed in place of the gastropore, and the anus is formed by breaking through the gastrula wall (protostomes include all other types of animals, except sponges, coelenterates and protozoa).
2. During the process of embryonic development, a secondary body cavity is formed - the coelom, but it is also possessed by all deuterostomes, annelids, mollusks, arthropods, bryozoans and brachiopods.
3. The metameric or segmental arrangement of the main organ systems is especially clearly expressed in arthropods and many worms. Metamerism is clearly expressed in chordates, but in terrestrial vertebrates in adulthood it is manifested only in the structure of the spinal column and some muscles, in the origin of the spinal nerves, and partly in the musculature of the abdominal wall.
4. Chordates, like most other multicellular animals, are characterized by bilateral (bilateral) symmetry: only one plane of symmetry can be drawn through the body, dividing it into two halves, which are mirror image each other.
Thus, the phylum chordates unites deuterostomes, bilaterally symmetrical coelomic animals with metamerism, expressed mainly in the early stages of embryonic development. They have an internal skeleton in the form of a chord with a neural tube lying above it; and under the notochord there is a digestive tube. The anterior end of the latter - the pharynx - is pierced by gill slits that open outward. The heart lies on the ventral side of the body under the digestive tube. In higher chordates, the notochord is replaced by the vertebral column; in terrestrial classes, the gill slits are overgrown and new respiratory organs - the lungs - develop.
Origin of chordates. Fossil remains of the ancestors of chordates have not been preserved. Therefore, one has to judge the early stages of their evolution largely by indirect data: by comparing the structure of adult forms and comparative research embryonic development.
The ancestors of chordates were sought among various groups animals, including annelids. For example, it was proposed to consider some sessile polychaetes (polychaete worms) like modern ones as the ancestors of chordates. Sabellidae And Serpulidae. It was assumed that these hypothetical ancestors of chordates switched to an active lifestyle, but began to move on the initially dorsal (dorsal) side of the body. The anal groove characteristic of these worms, stretching forward through the glandular field along the abdominal surface, could close, forming a neural tube connected by a neuro-intestinal canal with the intestinal tube, and glandular cells, having become part of the neural tube, provided the neurosecretory function of the nervous system. In this case, the predecessor of the notochord could be a connective tissue cord lying in the thickness of the ventral muscles of some polychaetes. The likelihood of such formation of the internal skeleton would seem to be confirmed by the formation of a cartilaginous gill-like skeleton in some modern polychaetes. The loss of polymeric segmentation (e.g. by gastrobreathers) is, from this point of view, a secondary phenomenon (Engelbrecht, 1969).
These witty ideas were not confirmed. Most zoologists believe that the predecessors of chordates were apparently coelomic worm-like animals that switched to a sedentary or sedentary lifestyle, which led to a decrease in the number of their body segments (probably to three) and the formation of a secondary mouth. They fed passively, filtering the water. These are oligomeric inhabitants seabed, evolving, gave rise to four types. Among them, echinoderms, having formed a water-vascular ambulacral system and a complex apparatus for capturing food, gained the ability to move on different soils and switched to active feeding on immobile and sedentary food objects. This ensured their biological success: in many biocenoses of the seabed, not only in shallow waters, but also at great depths, echinoderms thrive without serious competitors.
Pogonophora- a peculiar group of sessile animals, now classified as a special type (A.V. Ivanov, 1955), continues to cause controversy regarding their origin and position in the system. Pogonophorans sit in protective tubes and are distinguished by a very simplified structure: a central nervous system consisting of a dorsal trunk with a head ganglion, the absence of locomotor organs and a digestive tube. They live off of food substances dissolved in water - decomposition products of the “rain of corpses” that fall from the layers of water that lie above, rich in life. They are characterized by so-called extraintestinal digestion: absorption is carried out by the cells of the tentacles. Such passive feeding is possible and advisable in weakly moving water of the ocean depths.
The third branch of development led to the separation of chordates. Apparently, at the very beginning of evolution, the currently small group of hemichordates separated from it, which is now given the rank of phylum. Type hemichordate ( Hemichordata) includes two classes: pinnabranchids ( Pterobranchia) and enteric breathing ( Enteropneusta). Representatives of both classes have a three-membered body, consisting of a head lobe (proboscis), a collar and a trunk.
Cirrobranchs- sessile animals that form colonies in the form of bushes; Animals - zooids - sit in the cavities of the tubes (bush branches). The small hollow head lobe (proboscis) of the zooid has muscular walls and communicates with external environment small at times. Inside, at the base of the head lobe, there is a “heart” 1 and an excretory organ, and on its surface there is a glandular organ, the secretion of which serves to build the walls of the tubes - the branches of the colony. The collar, which has its own internal cavity, frames the mouth opening and serves as a support for the branching tentacles - the respiratory and food-gathering organs. Along the dorsal surface of the collar there is a short chain of nerve ganglia located intraepithelially, extending onto the proboscis. The body is occupied by a curved intestinal tube.
Representatives of the genera Cephalodiscus And Atubaria in the upper part of the intestinal tube they have a pair of “gill” openings that open outward, which, however, are not related to respiration and serve only to discharge water during filtration. The collar with tentacles and the base of the proboscis are supported by the notochord - a small elastic outgrowth of the dorsal part of the intestine, which allows us to consider the notochord as the rudiment (predecessor) of the notochord. In the body cavity (coelom) there are gonads that open outward through short ducts. From a fertilized egg, a mobile larva develops, capable of crawling and swimming, which soon settles on the bottom and after two days turns into an adult animal. The last way budding forms a new colony. Buds are formed on the stolon, in the caudal region of the body.
Colon-breathing have an elongated worm-shaped body; length from a few centimeters to 2-2.5 m ( Batanoglossus gigas). They lead a solitary lifestyle, are quite mobile, live mainly in shallow sea waters, but are also found at depths of up to 8100 m. They make U-shaped burrows in the ground by mining. Their walls are held together by mucus secreted by glandular skin cells.
The proboscis has muscular walls; through a small hole, its cavity can be filled with water, turning the proboscis into a burrowing tool. There is also a small coelom inside the collar. On the ventral side, between the proboscis and the collar, there is an oral opening leading to the pharynx (Fig. 4). The walls of the pharynx are pierced by numerous paired gill slits that open outward on the dorsal side of the body; At the bottom of the pharynx in some species a longitudinal thickening is formed, which can probably be considered as the rudiment of an endostyle. The pharynx passes into the intestine, ending in the anus at the posterior end of the body. Numerous blind hepatic processes extend from the dorsal surface of the anterior part of the intestine; they are visible from the outside as rows of tubercles. A small hollow elastic outgrowth of the pharyngeal wall, formed by vacuolated cells and strands of connective tissue, protrudes into the base of the proboscis, as in pinnatebranchs, the notochord. In Balanoglossus, several muscle bands are associated with the notochord, extending to the caudal part of the body. In this one can see the prototype of the myochordal complex, with the development and improvement of which the progress of chordates is associated.
Circulatory system open Two longitudinal vessels - dorsal and abdominal - are connected by transverse vessels passing along the partitions between the gill slits. The dorsal vessel opens into the head lacuna located above the notochord. Adjacent to it is the “heart” - a hollow muscular vesicle: its rhythmic contractions create blood flow. A folded formation penetrated by blood vessels protrudes into the cavity of the proboscis, performing the function of an excretory organ; its epithelium is similar to the epithelium of the excretory organs of chordates. Decay products diffuse into the cavity of the proboscis and are removed with water through the proboscis pore. Breathing is carried out both over the entire surface of the body and in the pharynx: oxygen enters the blood flowing through the vessels of the interbranchial septa. The nervous system consists of dorsal and ventral nerve cords connected by one or two peripharyngeal nerve rings (commissures). In the anterior part of the dorsal nerve cord there is usually a cavity similar to the neurocoelum of the neural tube of chordates. The sensory organs are represented by sensory epidermal cells, more numerous on the proboscis and the anterior part of the collar. The sensory cells scattered at the top of the proboscis are light sensitive.
Chordates are the most highly organized creatures of all representatives of the animal kingdom. Characteristics structures 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 during 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 types 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 connected motionlessly. 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 due to the fact that they live on land, breathe with the help of 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 the 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 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.
The phylum Chordata unites animals of different appearance, living conditions, lifestyle. Representatives of this type are found in all major environments of life: in water, on land, in the soil, in the air. They are distributed throughout the Earth. The number of species of modern representatives of chordates is about 40 thousand.
The phylum Chordata includes skullless, cyclostomes, fish, reptiles, amphibians, mammals and birds. Tunicates can also be classified as this type - this is a unique group of organisms that lives on the ocean floor and leads an attached lifestyle. Sometimes gastrobreathers, which have some characteristics of this type, are included in the phylum Chordata.
Characteristics of the type Chordata
Despite the wide variety of organisms, they all have a number of common features construction and development.
The structure of chordates is as follows: all these animals have an axial skeleton, which first appears in the form of a notochord or dorsal string. The notochord is a special non-segmented and elastic cord that embryonically develops from the dorsal wall of the embryonic intestine. The origin of the notochord is endothermal.
Further, this cord can develop differently, depending on the organism. It remains throughout life only in lower chordates. In most higher animals, the notochord is reduced, and in its place a vertebral column is formed. That is, in higher organisms, the notochord is an embryonic organ that is replaced by vertebrae.
Above the axial skeleton is the central nervous system, which is represented by a hollow tube. The cavity of this tube is called a neurocoel. Almost all chordates are characterized by a tubular structure of the central nervous system.
In most chordate organisms, the anterior section of the tube grows to form the brain.
The pharyngeal section (anterior) of the digestive tube comes out at two opposite ends. The openings that emerge are called visceral fissures. Lower organisms of the type have gills on them.
In addition to the three above-mentioned features of chordates, it can also be noted that these organisms have a secondary mouth, like echinoderms. The body cavity in animals of this type is secondary. Chordata are also characterized by bilateral body symmetry.
The phylum Chordata is divided into subtypes:
- Skullless;
- Tunicates;
- Vertebrates.
Subtype Skullless
This subphylum includes only one class - Cephalochordates, and one order - Lancelets.
The main difference between this subtype is that these are the most primitive organisms, and all of them are exclusively marine animals. They are widespread in the warm waters of oceans and seas of temperate and subtropical latitudes. Lancelets and epigonychites live in shallow water, mainly burying the back part of their body in the bottom substrate. They prefer sandy soil.
Feeds this type organisms with detritus, diatoms or zooplankton. They always breed in the warm season. Fertilization is external.
The lancelet is a favorite object of study, because all the characteristics of chordates are preserved for life, which allows us to understand the principles of the formation of chordates and vertebrates.
Subtype Tunicates
The subtype includes 3 classes:
- Salps;
- Ascidians;
- Appendiculars.
All animals of the subtype are exclusively marine.
The main difference between these chordates is that almost all organisms lack a notochord and a neural tube as adults. In the larval state, all the characteristics of the type in tunicates are clearly expressed.
Tunicates live in colonies or solitarily, attached to the bottom. There are significantly fewer free-swimming species. This subtype of animals lives in the warm waters of the tropics or subtropics. They can live both on the surface of the sea and deep in the ocean.
The body shape of adult tunicates is round, barrel-shaped. The organisms got their name due to the fact that their body is covered with a rough and thick shell - a tunic. The consistency of the tunic is cartilaginous or gelatinous; its main purpose is to protect the animal from predators.
Tunicates are hermaphrodites and can reproduce both sexually and asexually.
It is known that the ancestors of these organisms were free-swimming, but at present only tunicate larvae can move freely in the water.
Subphylum Vertebrates
Cranial animals are the highest subphylum. Compared to other subtypes, they have more high level organizations, which is evident from their structure, both external and internal. Among vertebrates, there are no species that lead a completely attached lifestyle - they actively move in space, looking for food and shelter, and a pair for reproduction.
By moving, vertebrate organisms provide themselves with the opportunity to change their habitat depending on changing external conditions.
The above general biological features are directly related to the morphological and physiological organization of vertebrates.
The nervous system of cranial animals is more differentiated than that of lower animals of the same type. Vertebrates have a well-developed brain, which contributes to the functioning of higher nervous activity. It is the highest nervous activity is the basis of adaptive behavior. These animals have well-developed sensory organs, which are necessary for communication with the environment.
As a result of the emergence of sensory organs and the brain, a protective organ such as the skull developed. And instead of a chord, this subtype of animals has a spinal column, which serves as a support for the entire body and a case for the spinal cord.
All animals of the subtype have a movable jaw apparatus and an oral fissure, which develop from the anterior section of the intestinal tube.
The metabolism of this subtype is much more complex than that of all the animals discussed above. Cranials have a heart that provides rapid blood flow. Kidneys are necessary for removing waste products from the body.
The subtype Vertebrates appeared only in the Ordovician-Silurian, but in the Jurassic period all currently known types and classes already existed.
The total number of modern species is slightly more than 40 thousand.
Classification of vertebrates
The phylum Chordata is very diverse. The classes existing in our time are not so numerous, but the number of species is enormous.
The cranial subtype can be divided into two groups, these are:
- Primary water organisms.
- Terrestrial organisms.
Primary water organisms
Proto-aquatic eggs are distinguished by the fact that they either have gills throughout their entire life or only in the larval stage, and during the development of the egg, embryonic membranes are not formed. This includes representatives of the following groups.
Section Agnathans
- Class Cyclostomes.
These are the most primitive cranial animals. They actively developed in the Silurian and Devonian; at present, their species diversity is not great.
Section Gastrostomata
Pisces superclass:
- Class Bony fish.
- Class Cartilaginous fish.
Superclass Quadrupeds:
- Class Amphibians.
These are the first animals to develop a jaw apparatus. This includes everything famous fish and amphibians. All of them actively move in water and on land, hunt and capture food with their mouths.
Terrestrial organisms
The group of terrestrial animals includes 3 classes:
- Birds.
- Reptiles.
- Mammals.
This group is characterized by the fact that in animals, during the development of the egg, embryonic membranes are formed. If the species lays eggs on the ground, the embryonic membranes protect the embryo from external influences.
All chordates of this group live mainly on land and have internal fertilization, which suggests that these organisms are more evolutionarily developed.
They lack gills at all stages of development.
Origin of chordates
There are several hypotheses for the origin of chordates. One of them suggests that this type of organisms originated from the larvae of intestinal-breathers. Most representatives of this class lead an attached lifestyle, but their larvae are mobile. Examining the structure of the larvae, one can see the rudiments of the notochord, the neural tube and other features of chordates.
Another theory states that the phylum Chordates evolved from the crawling, worm-like ancestors of the gastrobreathers. They had the rudiments of a chord, and in the pharynx, next to the gill slits, there was an endostyle - an organ that contributed to the secretion of mucus and the capture of food from the water column.
The article discussed the general characteristics of the type. Chordates are united by many similar features of all organisms, but still each class and each species has individual characteristics.
lecture 1: phylum chordates. general characteristics.
1. General characteristics phylum 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 around 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 increases ( gray matter) in the brain (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).
TO phylum Chordata include animals that have an internal axial skeleton - notochord - in the adult or embryonic period of life. In the process of evolution, chordates reached the highest level of organization and flourishing, compared to other types. They live in all areas of the globe and occupy all habitats.
In the phylum Chordates there are 3 subtype :
Tunicates,
Cephalochordates (Skullless) – class Lancelet,
Vertebrates (Cranial) - classes Cyclostomata, Cartilaginous fish, Bony fish, Amphibians, Reptiles, Birds, Mammals.
Main characteristics of chordates:
three-layer structure
bilaterally symmetrical animals
have a secondary body cavity and a secondary mouth
the complex structure and development of the gastrula, during which the notochord and neural plate are formed. The next stage is neurula - the formation of the neural tube
have an internal axial skeleton - a notochord: in skullless animals it remains throughout life, in vertebrates it is replaced by a cartilaginous or bony spine
The central nervous system looks like a tube located on the dorsal side of the body above the notochord. The cavity of the neural tube is the neurocoel. In most chordates, the anterior part of the neural tube grows and forms the brain (neurocoel - ventricles of the brain)
the digestive tube is located under the notochord. In its anterior section there are gill slits that communicate with the external environment and remain either throughout life (cranial animals, vertebrates - cyclostomes, fish), or only in the embryonic period of development (amphibians, terrestrial vertebrates)
the heart is located on the ventral side of the body and sends blood to the head end of the body
the outer integument has a two-layer structure and consists of the epidermis and connective tissue dermis
Chordates have bilateral symmetry of the body, a secondary body cavity (coelom), and a metameric (segmental) structure of many organs.
Subphylum Cephalochordae
Class Lancelets
A small group of primitive chordates that retain all the characteristics of the type throughout their lives (about 20 species of lancelets are known). They live exclusively in the seas and lead a bottom-dwelling lifestyle (in the sand).
Classic representative – lancelet.
This is a small translucent animal with a length 5-8 cm, his body has torpedo-shaped, developed caudal fin(in the form of a lancet) and paired abdominal folds(metapleural folds).
Internal axial skeleton represented by a chord covered with a dense connective tissue membrane.
Leather represented by a single-layer epidermis.
Musculature clearly segmented (muscle segments are called myomeres).
Oral opening surrounded by numerous tentacles.
By way of eating Lancelet is a filter feeder. Digestive system poorly differentiated. The pharynx is penetrated by gill slits that open into the peribranchial cavity. At the bottom of the pharynx lies a glandular formation that secretes mucus. Food particles arriving with a current of water adhere to the mucus and, with the help of cilia of the ciliated epithelium lining the pharynx, are directed to the intestines. The intestinal tube forms a blind protrusion - a hepatic outgrowth (similar to the real liver of vertebrates).
Circulatory system closed, one circle of blood circulation is developed, there is no heart. Blood flow is maintained by the pulsating abdominal aorta.
Excretory system is represented by numerous paired nephridia - tubes located segment by segment. The excretory openings open into the peribranchial cavity.
Breath carried out using gills.
Lancelets - dioecious animals, their gonads do not have their own excretory ducts.
Fertilization and development larvae (with metamorphosis) occur in water.
The neural tube stretches along the entire body above the notochord. Central nervous system formed by a tube with a neurocele inside. Peripheral nerves arise from the neural tube.
Sense organs are poorly developed, there are light-perceiving pigment spots, a tactile cell and an olfactory fossa.