Features of the musculoskeletal system in fish. Musculoskeletal system of fish. Musculoskeletal system of amphibians

Pisces is the largest species diversity a group of aquatic chordates, which is also the oldest. Fish inhabit almost all fresh and salt water bodies. All their organ systems are adapted to living in aquatic environment. According to accepted science, they belong to the domain Eukaryotes, the kingdom Animalia and the phylum Chordata. Let's take a closer look at the superclass.

Coverings of the body

The outer covering of a fish's body is skin and scales. There are rare exceptions when the scales are missing or modified. The skin is divided into dermis and epidermis. The epidermis of the superclass Pisces is not keratinized.

In the formation of scales main role It is the dermis that does this. The scales vary depending on the class of fish to which they belong.

available in the class Cartilaginous fish. It consists of dentin covered with enamel. It is this kind of scale that, in the course of evolution, turned into the teeth of sharks and rays. If a scale link is lost, it will not be restored.
Ganoid scales are characteristic of the order Sturgeon. It consists of bone plates coated with ganoin. This shell perfectly protects the body.
Cosmoid scales are observed in lobe-finned and lungfishes. It consists of cosmin and dentin.

The coloration of individuals of the superclass Pisces can be very diverse. Representatives of the fauna can be either painted in one color or be variegated, they can have a dull or, conversely, color that warns of danger.

Musculoskeletal system

Musculoskeletal system allows the fish to move and change position in environment. The skeleton of a fish is different from that of a land animal. Her skull has more than forty elements that can move independently. This allows the animal to stretch and spread its jaws, sometimes very widely.

The spine consists of individual vertebrae that are not fused together. It is divided into trunk and caudal sections. When swimming, the driving force is created by the fish's fin. They are divided into paired (thoracic, abdominal) and unpaired (dorsal, anal, caudal). In bony representatives of the superclass, the fin consists of bony rays, which are united by a membrane. The muscles help to unfold, fold and roll it, as the fish wishes.

Swimming of the inhabitants of the aquatic environment is possible thanks to muscles. They contract and the fish moves forward. Muscles are divided into “slow” and “fast” muscles. The first ones are needed for calm swimming and drifting. The second ones are for fast and powerful jerks.

Nervous system of fish

The fish brain is divided into sections. Each of them performs a specific function:

The forebrain consists of the diencephalon and the telencephalon. This department contains olfactory bulbs. They are the ones who receive signals from the external organs of smell. Fish that actively use their sense of smell during hunting have enlarged bulbs.
The midbrain has optical lobes in its cortex.
The hindbrain is divided into the cerebellum and medulla oblongata.

The spinal cord in representatives of the superclass Pisces runs along the entire length of the spine.

Circulatory system

Most representatives of the superclass have one circulation and a two-chambered heart. The circulatory system is closed; it transfers blood from the heart through the gills and body tissues. does not separate oxygen-rich arterial blood from oxygen-poor venous blood at all.

In fish they run one after another and are filled with venous blood. These are the venous sinus, atrium, ventricle, conus arteriosus. Blood can only move in one direction - from the sinus to the cone. Special valves help her with this.

Organs of gas exchange in fish

The gills of a fish are main body gas exchange. They are located on the sides of the oral cavity. In bony fishes they are covered by an operculum, in others they can freely open outwards. When ventilation of the gills occurs, water passes into the mouth, then into the gill arches. After this, it again comes out through the openings of the gills of the fish.

The structure of the gills is as follows: they have semi-permeable membranes, penetrated by blood vessels, and are located on bony arches. Gill filaments, penetrated by a tiny network of capillaries, help fish feel even more free under the water column.

In addition to gill respiration, fish can use another method of gas exchange:

Fish larvae can exchange gases through the surface of the skin.
Some species have lungs that store humidified air.
Some species of fish can breathe air on their own.

How does the digestive system of fish work?

Fish grasp and hold food with teeth, which are located in the oral cavity (as in most vertebrates). Through the pharynx, food enters the stomach through the esophagus. There it is processed gastric juice and the enzymes it contains. The food then moves into the intestines. Its remains are thrown out through the cloaca (anus).

What do the inhabitants of the aquatic environment eat? The choice is very wide:

Characteristics of the superclass Pisces cannot be complete without a description. Life in water leads fish to a number of problems with osmoregulation. Moreover, these problems are typical for freshwater and sea fish the same. Cartilaginous fish are isosmotic. The salt concentration in their body is lower than in the environment. Osmotic pressure equalizes due to high content in the blood of fish there is urea and trimethylamine oxide. Low concentration salts support the cartilaginous class due to the work of the rectal gland and the excretion of salts by the kidneys.

Teleost fish are not isosmotic. During evolution, they were able to develop a mechanism that retains or removes ions. The biology of the Chordata type helps fish excrete salts into the sea. This happens because the fish are losing water. Chloride and sodium ions are excreted by the gills, and magnesium and sulfates are excreted by the kidneys.

Freshwater fish have exactly the opposite mechanism. The concentration of salt in the body of such creatures is higher than in the environment. Their osmotic pressure is equalized due to the secretion large quantity urea and capture the desired ions from body of water gills.

Superclass Pisces: how does reproduction occur?

Fish have several types of reproduction. Let's look at each of them in more detail.

Bisexual reproduction is the most common form. In this case, the two sexes of fish are clearly separated. This is often visible even from external signs(for example, color). Most often, males have secondary sexual characteristics. They can manifest themselves in differences in body sizes between males and females, and differences in body parts (for example, a longer fin). Males during bisexual reproduction can be monogamous, polygamous, or have promiscuous, chaotic relationships (promiscuity).
Hermaphroditism - in such fish the gender can change throughout life. Protoandria at the beginning of life are males, then after body restructuring they become females. Protogyny is a form of hermaphroditism where all males are transformed females.
Gynogenesis is a method of reproduction for fish species represented only by females. It is rarely found in nature.

Fish can reproduce through viviparity, oviparity, and ovoviviparity.

Class Bony fish

Superclass Fishes are divided into two classes: Cartilaginous and Bony fish.

Bony fish are the most numerous group. They number more than 19 thousand species. Their skeleton is bony. In some cases, the skeleton may be cartilaginous, but then it is additionally strengthened. Bony fish have a swim bladder. There are over 40 units in this class. Let's talk in more detail about the most numerous.

The order Sturgeons includes ancient bony fishes such as sturgeon, beluga, and sterlet. They are distinguished by the presence of a snout and mouth on the ventral side of the body. The mouth has the appearance of a transverse slit. The basis of the skeleton is cartilage. Sturgeon live only in the Northern Hemisphere.
The Herring order is a schooling sea fish that feeds on plankton. Herring, Baltic herring, sardines, anchovies are commercial fish. They lay eggs on the ground or algae.
The order Salmonidae are freshwater fish that lay eggs on the bottom. They are found in the Northern Hemisphere. They are valuable commercial fish with delicious meat and caviar. The main representatives are salmon, chum salmon, pink salmon, trout, and brown trout.
The order Cypriniformes are freshwater fish without jaw teeth. They crush food with their pharyngeal teeth. The order includes commercial fish (roach, bream, tench, ide) and fish artificially bred in reservoirs (carp, grass carp, silver crucian carp).
The order Lungbreathers is the oldest order. They can breathe through gills and lungs (hollow outgrowths on the wall of the esophagus). They have adapted to life in hot countries and drying up water bodies. Prominent representatives of the order are the Australian horntooth and the American scalefish.

Cartilaginous fish

The main difference between cartilaginous and bony fish lies in the structure of the skeleton, the absence or presence of gill covers and a swim bladder. The class Cartilaginous fish is represented by inhabitants of the seas that have a cartilaginous skeleton throughout their lives. Since there is no swim bladder, representatives of this class swim actively so as not to sink to the bottom. Like sturgeons, the mouth has the appearance of a transverse slit, and a snout is present.

Cartilaginous fishes include only two orders. These are Sharks and Rays. Sharks have a torpedo-shaped body; they are active swimmers and fearsome predators. Their powerful jaws strewn sharp teeth. At the same time, the largest sharks feed on plankton.

Stingrays have a flattened body with gills near the belly. The fins of the fish are greatly enlarged. Stingrays feed on bottom animals and fish.

Use of fish resources and their protection

Fish has great value in human life, being one of the main foodstuffs. Every year, about 60 million tons of fish are caught around the world. At the same time, the most commonly caught are herring, cod and mackerel.

IN Lately The fish catch is noticeably decreasing. This is due to the deteriorating environmental situation in the world. Stocks are being depleted due to overfishing, destruction of certain fish species, pollution of their spawning grounds, and salt poisoning. heavy metals. Gradually, humanity is moving from uncontrolled fishing to growing fish as a commercial object.

The best successes in fish farming are those that go back far into history. They exercise full control over the cultivation of products from larvae to marketable products. Fish are bred in artificial ponds for various purposes: feeding, nursery, wintering, and so on. There are also special ponds for spawning. They always have small size and warm up well.

Musculoskeletal system

Bony fish have skeletons that are more or less bony. Bones are formed in two ways. Cutaneous or integumentary bones arise in the connective tissue layer of the skin, and cartilaginous bones arise as a result of the replacement of cartilage with bone substance. The skeleton consists of the skull, spine and fin skeleton. The skull contains jaws and gill arches.

The muscles of bony fish are represented by two main muscles located along the body and separated by partitions made of connective tissue into separate segments. The muscles of the pharynx and the muscles that control the movement of the fins are also developed.

Digestive system

The digestive tract of bony fishes includes the following sections: oral cavity, pharynx, esophagus, stomach and intestines. The intestines end anus. There is no cloaca. In primitive groups there is a spiral valve. There are no salivary glands. Teeth calculus. The digestive glands are the liver and pancreas. A thin-walled outgrowth of the esophagus is the swim bladder, with the help of which the fish regulates its buoyancy.

CLASS CARTILAGE FISH Skeleton. Due to the need to have more reliable protection for the nervous system and other organs and a stronger support for greatly increased muscular system the fish in question developed a cartilaginous skeleton, often calcified (Fig. 79). Brain department skulls larger than those of jawless ones, closed on all sides (with a small hole in the middle of the roof). The visceral part of the skull includes: two palatoquadrate cartilages (right and left), which act as the upper jaws; two Meckel's cartilages (right and left), serving as lower jaws; the hyoid arch, consisting of two upper cartilages (right and left), which are attached to the skull where the labyrinths are located, and two lower cartilages (hyoid); segmented gill arches (right and left, the number of which in most species is 5-7). In place of the notochord it developed spinal column. Each vertebra consists of a body with concave surfaces (anterior and posterior). Such vertebrae are called biconcave or amphicoelous. The notochord is preserved as a narrow rod passing through the centers of the vertebral bodies. Two processes extend upward from the vertebral bodies, which form the superior arch with the spinous process. From the vertebral bodies, transverse processes extend downwards, forming the lower arch, and from them - short ribs. The canal, which is formed by holes in the upper arches of the vertebrae and intercalated plates between the vertebrae, contains the spinal cord.

Digestive system. The vast majority of plastibranchs are carnivores. The oral cavity is extensive, the jaws are armed with strong, sharp teeth that arose from placoid scales that moved into the mouth during evolution. The teeth are arranged in several rows. As the teeth in the front row wear out, they are replaced by the teeth in the next row. Behind oral cavity there is a pharynx, a short esophagus, a voluminous stomach, an intestine and a cloaca

The ducts of the liver and pancreas open into the initial part of the intestine. The intestine is shorter than that of bony fishes, but its internal surface is greatly enlarged due to the presence of a spiral fold, the number of revolutions of which can reach fifty.

The liver, consisting of three lobes, is very large, in some species its mass reaches 14-25% of the entire body. It can accumulate a lot of fat, which is consumed during periods of food shortage or increased energy expenditure. The accumulation of fat reduces the specific body mass, which helps to increase the buoyancy of these fish. The pancreas does not yet have a compact shape and is represented, as in cyclostomes, in separate areas adjacent to the walls of the beginning of the intestine and liver.

The food for elasmobranchs is various fish. Many of them eat crustaceans, mollusks, worms and other invertebrates. Interestingly, the largest sharks - whale sharks (body length 15 m) and giant sharks (body length 20 m) - feed, like baleen whales, on plankton, filtering water through their mouths.

U cartilaginous fish skeleton more advanced, compared to cyclostomes. Expressed differentiation to departments, the number is increasing components elements. Chord almost is being forced out developing cartilaginous bodies biconcave (amphicoelous) vertebrae The spinal column is divided into two sections - trunk and caudal. Scull also has more complex structure - appears occipital region, is developing jaw apparatus, the connection between the brain and visceral parts is strengthened ( amphistyly and hyostyly). The limbs and their attachment become more complex. Despite the cartilaginous basis, the skeleton has great strength.

Has undergone significant changes muscular system, which increased in mass and underwent further differentiation, although it largely remained metamerically there is. Complications in supporting apparatus are not accidental, since cartilaginous fish are large in size, have significant biomass and are in almost constant motion.

Structure of the skull

The head skeleton of cartilaginous fish consists of two interconnected sections – cerebral and visceral. Each of them, in turn, is usually divided into component parts. IN brain section included roof, sides, bottom and back. Visceral department contains jaw, hyoid arches and skeleton of the branchial apparatus (Fig. 21).

Rice. 21. Shark Skull:

1 – nasal capsule, 2 – rostrum, 3 – orbit, 4 – occipital capsule, 5 – palatoquadrate cartilage, 6 – Meckel’s cartilage, 7 – labial cartilages, 8 – hyomandibular (suspension), 9 – hyoid, 10 – branchial arches .

Brain skull sharks serve as protection for the brain and consist from the braincase, paired capsules of the sensory organs and rostrum. From these cartilaginous formations are formed the following departments:

Roof of the skull – incomplete, has a hole (fontanelle), which is covered with dense connective tissue. Sides of the skull form large depressions - eye sockets, and behind them, growing into the braincase, are paired auditory capsules. At the front end are nasal capsule And rostrum from three rod-shaped cartilages, fused together and supporting the snout. On the sides of the base of the rostrum lie olfactory capsules, on the underside of which there are large holes. The capsules of the sensory organs, merging with each other, form the so-called orbit. The walls of the skull are pierced with openings for the passage of nerves and blood vessels.

In some cartilaginous fish (sawfish, sawfish) rostrum is very elongated and is flattened, lined with sharp teeth on the sides, which are modified placoid scales, and serves as a weapon of attack and defense.

Occipital region comprises unpaired cartilage, evolutionarily arose from the first vertebra; it contains in the middle big hole to connect the brain and spinal cord.

Floor of the skull not formed, the brain is protected from below by the cartilaginous elements of the visceral apparatus.

Visceral skull evolutionarily formed from gill arches that supported the pharyngeal region of ancient fish. In modern cartilaginous fish, as mentioned above, it is represented by three parts - maxillary, hyoid arches and arches of the gill apparatus.

Front component - jaw arch consists of two paired elements. One pair growing together into the palatoquadrate cartilage, forms upper jaw. Another pair in the form Meckel's cartilage composes lower jaw. On both jaws there are paired labial cartilages, increasing the surface of attachment of powerful visceral muscles. Both jaws are equipped with teeth derived from placoid scales.

Hyoid arch located behind the jaw arch. Its basis is paired hyoids, which are theirs upper ends attached to hyomandibular cartilages (hyomandibulare). Each of them, with its upper end, is attached to the brain skull in the region of the auditory capsule, while the lower end is connected through fibrous tissue to the maxillary arch and the middle element of the hyoid arch - hyoid. Therefore, the hyomandibular plays role suspension for jaws.

This type of attachment of the visceral skull to the brain is called hyostyly. A number of primitive sharks have amphistyly in the form of a combination of hyostyly with additional attachment of the process of the palatoquadrate cartilage to the base of the medulla. The right and left hyoids at the level of the bottom of the pharynx are connected to each other by means of unpaired cartilage - copulas, or sublingual cartilage.

Skeleton of the gill apparatus, next to the hyoid arch, represents five pairs of arcs. Each gill arch consists of four doubles elements that are movably connected to each other, and one unpaired, through which the right and left sides of the arcs are connected. Numerous cartilaginous rays extend from the hyoid and branchial arches, supporting the walls of the interbranchial septa.

Spine shark is firmly articulated with the occipital region brain skull and stretches to the end of the tail, entering its upper blade. There are two sections in the spine - trunk and caudal. The vertebrae of a shark, like all cartilaginous fish, are biconcave ( amphicoelous). The notochord is preserved only in the intervertebral spaces and in the center of the vertebral body.

Every vertebra(Fig. 22) consists of vertebral body, superior and inferior arches. Between the upper arches of the vertebrae there are cartilaginous insert plates. The ends of the upper arcs, connecting, form spinal canal.

The lower arches in the vertebrae of the trunk are short, directed somewhat to the sides and form transverse processes, to which ribs are articulated. In the caudal section, these arches, closing, form hemal channel where the caudal artery and vein pass.

Amphibians(they are amphibians) - the first terrestrial vertebrates to appear in the process of evolution. However, they still retain close connection with the aquatic environment, usually living in it at the larval stage. Typical representatives of amphibians are frogs, toads, newts, and salamanders. They are most diverse in tropical forests, as they are warm and damp. There are no marine species among amphibians.

General characteristics of amphibians

Amphibians are a small group of animals, numbering about 5,000 species (according to other sources, about 3,000). They are divided into three groups: Tailed, Tailless, Legless. Frogs and toads familiar to us belong to the tailless ones, newts belong to the tailed ones.

Amphibians develop paired five-fingered limbs, which are multi-membered levers. The forelimb consists of the shoulder, forearm, and hand. Hind limb - from the thigh, lower leg, foot.

Most adult amphibians develop lungs as respiratory organs. However, they are not as perfect as in more highly organized groups of vertebrates. Therefore, skin respiration plays an important role in the life of amphibians.

The appearance of lungs in the process of evolution was accompanied by the appearance of a second circulation and a three-chambered heart. Although there is a second circuit of blood circulation, due to the three-chambered heart there is no complete separation of venous and arterial blood. Therefore, most organs receive mixed blood.

The eyes not only have eyelids, but also lacrimal glands for wetting and cleansing.

The middle ear with the eardrum appears. (In fish, only internal.) The eardrums are visible, located on the sides of the head behind the eyes.

The skin is bare, covered with mucus, and contains many glands. It does not protect against water loss, so they live near bodies of water. Mucus protects the skin from drying out and bacteria. The skin consists of epidermis and dermis. Water is also absorbed through the skin. Skin glands multicellular, in fish unicellular.

Due to the incomplete separation of arterial and venous blood, as well as imperfect pulmonary respiration Amphibians have a slow metabolism, just like fish. They are also cold-blooded animals.

Amphibians breed in water. Individual development proceeds with transformation (metamorphosis). The frog larva is called tadpole.

Amphibians appeared about 350 million years ago (at the end of the Devonian period) from ancient lobe-finned fish. Their heyday occurred 200 million years ago, when the Earth was covered with huge swamps.

Musculoskeletal system of amphibians

Amphibians have fewer bones in their skeletons than fish, as many bones are fused while others remain cartilage. Thus, their skeleton is lighter than that of fish, which is important for living in air environment, which is less dense than water.

The brain skull is fused with upper jaws. Only the lower jaw remains mobile. The skull retains a lot of cartilage that does not ossify.

The musculoskeletal system of amphibians is similar to that of fish, but has a number of key progressive differences. So, unlike fish, the skull and spine are movably articulated, which ensures the mobility of the head relative to the neck. First appears cervical region spine, consisting of one vertebra. However, the mobility of the head is not great; frogs can only tilt their heads. Although they have cervical vertebra, in appearance there is no neck body.

In amphibians, the spine consists of more departments than in fish. If fish have only two of them (trunk and caudal), then amphibians have four sections of the spine: cervical (1 vertebra), trunk (7), sacral (1), caudal (one tail bone in tailless amphibians or a number of separate vertebrae in tailed amphibians) . In tailless amphibians, the caudal vertebrae fuse into one bone.

The limbs of amphibians are complex. The anterior ones consist of the shoulder, forearm and hand. The hand consists of the wrist, metacarpus and phalanges of the fingers. The hind limbs consist of the thigh, tibia and foot. The foot consists of the tarsus, metatarsus and phalanges.

The limb girdles serve as support for the skeleton of the limbs. The girdle of the forelimb of an amphibian consists of a scapula, clavicle, and crow bone (coracoid), common to the girdles of both forelimbs of the sternum. The clavicles and coracoids are fused to the sternum. Due to the absence or underdevelopment of the ribs, the belts lie deep in the muscles and are in no way indirectly attached to the spine.

The girdles of the hind limbs consist of the ischial and iliac bones, as well as pubic cartilage. Fusing together, they articulate with the lateral processes of the sacral vertebra.

The ribs, if any, are short, chest do not form. Tailed amphibians have short ribs, while tailless amphibians do not.

In tailless amphibians, the ulna and radius fuse, and the bones of the lower leg also fuse.

The muscles of amphibians have a more complex structure than those of fish. The muscles of the limbs and head are specialized. Muscle layers break down into individual muscles, which provide movement of some parts of the body relative to others. Amphibians not only swim, but also jump, walk, and crawl.

Digestive system of amphibians

General plan of the building digestive system amphibians are similar to fish. However, some innovations are emerging.

The anterior tip of the tongue of frogs grows to lower jaw, and the rear one remains free. This structure of the tongue allows them to catch prey.

Amphibians appear salivary glands. Their secretion moistens food, but does not digest it in any way, since it does not contain digestive enzymes. The jaws have conical teeth. They serve to hold food.

Behind the oropharyngeal cavity is a short esophagus that opens into the stomach. Here the food is partially digested. The first section of the small intestine is duodenum. A single duct opens into it, into which the secretions of the liver, gallbladder and pancreas enter. Digestion of food is completed in the small intestine and nutrients are absorbed into the blood.

Undigested food remains enter the large intestine, from where it moves to the cloaca, which is an extension of the intestine. The ducts of the excretory and reproductive systems also open into the cloaca. From her undigested remains fall into external environment. Fish do not have a cloaca.

Adult amphibians feed on animal food, most often various insects. Tadpoles feed on plankton and plant matter.

1 Right atrium, 2 Liver, 3 Aorta, 4 Oocytes, 5 Colon, 6 Left atrium, 7 Ventricle of the heart, 8 Stomach, 9 Left lung, 10 Gallbladder, 11 Small intestine, 12 Cloaca

Respiratory system of amphibians

Amphibian larvae (tadpoles) have gills and one circulation (like fish).

In adult amphibians, lungs appear, which are elongated sacs with thin elastic walls that have a cellular structure. The walls contain a network of capillaries. The respiratory surface of the lungs is small, so the bare skin of amphibians also participates in the breathing process. Up to 50% of oxygen enters through it.

The mechanism of inhalation and exhalation is ensured by the raising and lowering of the floor of the oral cavity. When lowering, inhalation occurs through the nostrils; when raising, air is pushed into the lungs, while the nostrils are closed. Exhalation is also carried out by raising the bottom of the mouth, but at the same time the nostrils are open and the air comes out through them. Also, when you exhale, the abdominal muscles contract.

Gas exchange occurs in the lungs due to the difference in gas concentrations in the blood and air.

The lungs of amphibians are not well developed enough to fully ensure gas exchange. Therefore, skin breathing is important. Drying out amphibians can cause them to suffocate. Oxygen first dissolves in the fluid covering the skin and then diffuses into the blood. Carbon dioxide also first appears in liquid.

In amphibians, unlike fish, nasal cavity has become through and is used during breathing.

Underwater, frogs breathe only through their skin.

Circulatory system of amphibians

A second circle of blood circulation appears. It passes through the lungs and is called the pulmonary circulation, as well as the pulmonary circulation. The first circle of blood circulation, passing through all organs of the body, is called major.

The heart of amphibians is three-chambered, consisting of two atria and one ventricle.

IN right atrium arrives deoxygenated blood from body organs, as well as arterial from the skin. IN left atrium arrives arterial blood from the lungs. The vessel entering the left atrium is called pulmonary vein.

Contraction of the atria pushes blood into common ventricle hearts. Here the blood is partially mixed.

From the ventricle, blood is sent through separate vessels to the lungs, body tissues, and head. The most venous blood from the ventricle enters the lungs through the pulmonary arteries. Almost pure arterial blood flows to the head. The most mixed blood entering the body flows from the ventricle into the aorta.

This division of blood is achieved by a special arrangement of vessels emerging from the distribution chamber of the heart, where blood enters from the ventricle. When the first portion of blood is pushed out, it fills the closest vessels. And this is the most venous blood that enters pulmonary arteries, goes to the lungs and skin, where it is enriched with oxygen. From the lungs, blood returns to the left atrium. The next portion of blood - mixed - enters the aortic arches, going to the organs of the body. Most arterial blood enters the distant pair of vessels ( carotid arteries) and goes to the head.

Excretory system of amphibians

The kidneys of amphibians are trunk, have oblong shape. Urine enters the ureters, then flows along the wall of the cloaca into bladder. When the bladder contracts, urine flows into the cloaca and then out.

The excretion product is urea. Its removal requires less water than the removal of ammonia (which is produced by fish).

Reabsorption of water occurs in the renal tubules of the kidneys, which is important for its conservation in air conditions.

Nervous system and sensory organs of amphibians

Key changes in nervous system amphibian compared to fish did not happen. However, the forebrain of amphibians is more developed and divided into two hemispheres. But their cerebellum is less developed, since amphibians do not need to maintain balance in water.

Air clearer than water Therefore, vision plays a leading role in amphibians. They see further than fish, their lens is flatter. There are eyelids and nictitating membranes (or an upper fixed eyelid and a lower transparent movable one).

In the air sound waves spread worse than in water. Therefore, there is a need for a middle ear, which is a tube with an eardrum (visible as a pair of thin round films behind the eyes of a frog). From eardrum sound vibrations through auditory ossicle are transmitted inner ear. Eustachian tube connects the middle ear cavity with the oral cavity. This allows you to reduce pressure drops on the eardrum.

Reproduction and development of amphibians

Frogs begin to reproduce at about 3 years of age. Fertilization is external.

Males secrete seminal fluid. In many frogs, males attach themselves to the backs of females and, while the female spawns eggs over several days, waters them with seminal fluid.

Amphibians spawn less eggs than fish. Clusters of eggs are attached to aquatic plants or float.

The mucous membrane of the egg in water swells greatly and refracts sunlight and heats up, which contributes to faster development of the embryo.

Development of frog embryos in eggs

An embryo develops in each egg (in frogs it usually takes about 10 days). The larva that emerges from the egg is called a tadpole. It has many features similar to fish (two-chambered heart and one circulation, breathing with gills, lateral line organ). At first, the tadpole has external gills, which later become internal. Appear hind limbs, then the front ones. The lungs and the second circle of blood circulation appear. At the end of metamorphosis, the tail resolves.

The tadpole stage usually lasts several months. Tadpoles feed on plant matter.

Friends! We continue to study animals belonging to the phylum Chordata and the subphylum Vertebrata or Cranial. Today we move on to the Pisces superclass. This is a fairly extensive topic and its study will be divided into several video lessons.

Today we will talk about general characteristics and the taxonomy of the superclass of Fish, in the next two issues we will analyze in detail the structure of fish using the example of river perch, and then move on to consider the characteristics of reproduction and study the diversity of fish orders.

External structure of fish

Fish are aquatic animals. In order to actively move in the aquatic environment, the body of fish has a streamlined shape.

The body of fish can be divided into:

head
torso
and tail

The boundary between the head and the body is the posterior edge of the gill covers, and the boundary between the body and the tail is the anal fin.

The top of the fish body is covered with skin, which consists of:

corium or dermis
and multilayered epidermis (as in all vertebrates).

The epidermis contains numerous mucous glands; the top of the epidermis in most fish is covered with scales.

The streamlined body shape, mucous glands and scales help the fish move quickly and easily in the water.

They move with the help of the bends of the body and with the help of paired pectoral and ventral fins, which are mainly responsible for vertical movement, as well as an unpaired caudal fin, which serves as a rudder.

Paired fins of fish - pectoral and ventral, unpaired - dorsal, anal and caudal

Also unpaired fins in fish include the dorsal and anal fins, which stabilize the body of the fish in an upright position.

Fins:

paired breasts
paired abdominal
unpaired dorsal (1 or more)
unpaired anal
unpaired caudal

Musculoskeletal system of fish

Fish have a well-developed skeleton, which is divided into:

1. axial skeleton , which includes:

spine,
skull or skeleton head
and ribs

2. skeleton of limbs, which includes:

skeleton of paired fins (free part and belts)
and the skeleton of unpaired fins.

Fish skeleton - the picture shows the skeleton of a bony fish

The skeleton of a fish consists of a skull, spine, ribs and a skeleton of paired and unpaired fins

In representatives of the class Cartilaginous fish, the skeleton consists only of cartilage tissue. Representatives of the class Bony fish have both cartilage and bone tissue in their skeleton.

The spine provides support and protective functions- The spinal cord is protected by the vertebral arches. The spine consists of two sections - the trunk and the caudal. The vertebrae of the trunk spine have lateral processes to which the ribs are attached.

Head skeleton presented cranium, with which the jaws and gill arches are connected, and in bony fishes also the gill covers. Cartilaginous fish do not have gill covers.

The digestive system consists of the mouth, pharynx, esophagus, stomach and intestines, into which the liver and gallbladder ducts open, as well as the pancreas. The intestine ends at the anus, which opens in front of the anal fin.

Only bony fish have a swim bladder.

Fish have a swim bladder, which is an outgrowth of the intestinal tube. The swim bladder is filled with gases and can expand and contract. In this case, the specific density of the body changes and the fish can move in the water column in the vertical direction. Only bony fish have a swim bladder; cartilaginous fish do not.

Respiratory system fish

Fish breathe using gills

Fish respiration is carried out using gills. Water enters the mouth, then from the pharynx the water passes through the gills into the external environment, while blood vessels located in the gill filaments are saturated with oxygen.

Circulatory system closed fish

The circulatory system has one circulation in all fish except lungfish. There is a two-chambered heart consisting of an atrium and a ventricle.

The nervous system consists of:

central section, which is represented by the brain and spinal cord and
peripheral section, consisting of cranial and spinal nerves.

The brain of fish, like all vertebrates, consists of five sections.

The nervous system of fish consists of the brain and spinal cord and the nerves coming from them

Well developed olfactory lobes forebrain, since for fish the chemical sense organs - smell and taste - play a very important role. The visual centers are located in the midbrain.

The cerebellum is also well developed, which is responsible for a variety of movements. There are lateral line organs that allow fish to determine the direction of water movement. There are organs of balance and hearing.

Excretory system fish consists of kidneys, ureters and bladder.

The excretory system is represented by paired ribbon-shaped kidneys, ureters and bladder, which opens into the urethra, which is located next to the anus.

Reproductive system of fish

Most fish are dioecious; males have two testes and females have two ovaries. Females spawn eggs (eggs) into the water, males spawn sperm. Fertilization occurs in the external environment.

Fish eggs - eggs

In many cartilaginous fish and in some bony fish, fertilization is internal; females give birth to fry.

Taxonomy of fish

IN currently About 30 thousand species of fish are known. The taxonomy of fish is quite complex; we will consider a somewhat simplified diagram. Currently in different sources can be found various options systematics.