Fish are vertebrates that live in water bodies and breathe with gills. There are more than 3 thousand species of them in the world. It is believed that it was they who first came out on land, giving rise to land animals. What classes and orders of fish are there? How do they differ from each other? Which order does the moonfish belong to - the heaviest fish in the world? We will answer all these questions in this article.

What makes fish unique?

Fish are an integral part of many ecosystems and important participants in the food chain. They are widespread on the planet, inhabiting salt and fresh water bodies from the oceans to alpine lakes located at an altitude of more than 6 kilometers.

They spend most of their life in water, so the gills are the main respiratory apparatus for them. In many orders of fish, there are representatives who are able to briefly crawl to the surface (muddy jumper, climbing perch, some even developed additional respiratory organs - lungs (lung-breathing fish - protopterus, cattle-toothed, etc.).

Almost constant life under water demanded from fish special devices... Their outer covers are represented by scales - plates of dentin, kosmin or gaonin, which are superimposed on each other like shingles.

They move with the help of fins, and to reduce the body, their body is streamlined. Many fish have. By regulating pressure, it promotes vertical movements of the animal in the water column, and also helps them to stay at a certain depth.

Fish classification

Fish are a group of chordates, within which several classes are distinguished. Their number differs in various sources. Usually they are divided into cartilaginous and bone. Sometimes Bony fishes are distinguished as a superclass, and within it the classes of ray-finned and lobe-finned are distinguished.

The orders of cartilaginous fishes are chimera-like, catran-like, skate-like, sea angels, multigill, llam-like and others. There are about 13 of them in total, and they are represented by various stingrays and chimeras.

The skeleton of these fish is composed of cartilage. In stingrays and sharks, the gills are not covered with a lid, but go out with slits. There is no swim bladder, which forces them to be constantly in motion, otherwise they will fall to the bottom. Some species do not lay eggs, but reproduce by live birth.

The orders of the bony fish class are more numerous. As the name suggests, their skeleton is made of bones. The gills are part of the skeleton, they consist of petals and stamens, and are covered from above with lids.

It is impossible to list all the orders of fish at once in one article, so below we will describe the most interesting or common of them.

Perches

The largest order of fish, which covers about 7-8 thousand species. Most of them are commercial. The main feature of the fish of the order perciformes is the ctenoid scales. Its edges are not even, but are divided into many small teeth. Their pectoral fins are located under the pectorals, and some of the radial fins are turned into spines.

Perchiformes vary greatly in size. Some species reach only a few centimeters (Lucion mystichtis), while others grow up to 3 meters (bluefin tuna). Typical representatives are mackerel, gobies, pike perch, tuna, gourami, swordfish. But sea bass do not belong to them and belong to the order of scorpion-like.

Chimeras

Fish of the order chimera-like have a somewhat bizarre appearance. Their body is elongated and strongly narrowed towards a whip-like tail. A spine is located in front of the two dorsal fins, which can hide in a fold on the back.

The nose is pointed and triangular in shape. In some species, it is strongly elongated, and resembles a proboscis. The mouth is located below. The pectoral fins are large and wing-like in shape.

Chimeras swim slowly, "hovering" in water space. They live at great depths or shelf shallows. They are found in the Indian, Atlantic and Pacific Oceans. They reproduce by laying eggs.

Sturgeon

In terms of structure, sturgeons occupy an intermediate place between cartilaginous and bone detachments fish. Usually they are classified as bony and cartilage subclass. These include beluga, all kinds of sturgeon, kaluga, sterlet, etc.

Their skeleton consists of cartilage, has a notochord and is not divided into vertebrae. The body of fish is elongated and covered with five rows of large bony plates, between which are located smaller scales. The mouth is located at the bottom. In front of him are four antennae, which play the role of organs of touch.

Sturgeons live in the rivers and seas of the Northern Hemisphere. Fishing for them is very common, caviar is especially appreciated. It's pretty large fish... Belugas, for example, reach 4-9 meters, sturgeons - 6 meters.

Blowfish

This order of bony fish includes about 250 species. Most representatives have an unusual body shape: spherical, flattened disc-shaped, cubic, etc. The mouth of the fish is usually small, the bones of the upper jaw are tightly closed. Instead of ordinary scales, their body is covered with thorns or small needles.

They inhabit warm ocean waters near the equator, preferring coral reefs. Notable representatives are the hedgehog fish, the moon fish, the cube box and others. The moonfish is the heaviest fish in the world. Its weight can exceed 20 tons. It has a disc-like shape, flattened from the sides and reaches up to 2 meters in diameter.

Flounders

Flounders are flat fish that swim on their sides. They also lie on their side, so their eyes are placed only on one side. The color, as a rule, is close to the color of the seabed. This is necessary for camouflage, because almost all fish of the order are predators and feed on crustaceans, molluscs and small fish.

They inhabit the seas from tropical to temperate zones, inhabiting mainly near the bottom. Fish prefer shallow waters; individual species easily swim into river mouths. These include flounder, halibut, limanda. The smallest representatives are 7-8 centimeters in size, the largest are about 5 meters.

Herring

Herring is one of the most primitive orders of bony fish. Their body is slightly flattened and covered with semicircular scales. The skull of many fish is made up of cartilage tissue. The fin rays are very soft, which is why the detachment is often called "soft-finned". The detachment includes the Atlantic Menhaden, Baltic herring, Pacific herring, sardine, sprats, anchovy, Baltic herring, sprat.

These fish are very diverse in their way of life; many are capable of making long migrations. They are common in all oceans of the world, especially in tropical regions and subtropical regions. The subpolar regions are inhabited only by certain species, some also live in fresh water bodies. Most are pelagic fish that live in the upper layers of the ocean.

Eels

Unusual representatives of bony fish are the order of eels. Due to their long, elongated body, they can be confused with snakes. However, the body of eels does not taper towards the tail and is often not even flattened laterally.

They wriggle around. The fish have no pelvic fins, exactly like scales. The skin is covered with mucus. Like snakes, they may not have ribs, and the ridge is up to 300 vertebrae. Most eels are venomous and predatory. Particularly large species (giant moray eels) even attack reef and tiger sharks.

They prefer warm water bodies. They are represented by a variety of different types moray eels and eels. The only freshwater family is river eels. They live in water bodies that belong to the basins of the Atlantic, Pacific and Indian Ocean.

Gray sharks

Among all sharks, the most numerous is the order of karcharid or gray sharks. It includes more than 250 species, including hammerhead sharks, tiger sharks, silk sharks, blunt sharks, etc. Its representatives are considered one of the most dangerous inhabitants of the deep sea. On account of them, many human victims.

They live in the coastal zones of the seas of the tropical, subtropical and temperate zones. The fish are constantly moving, then moving away into the depths of the ocean, then swimming in shallow waters. Some species also appear in fresh water bodies.

Gray sharks have five pairs of gill slits, two dorsal and one anal fins. They reproduce either by laying eggs or by live birth.

They have a large mouth located below, and the snout is extended forward. In some sharks, it is strongly rounded (in blunt sharks). The hammerhead shark has a specific look. Their muzzle is flattened at the top and wide at the sides, reminiscent of the leading edge of a hammer. The first dorsal fin is curved in the shape of a sickle.

Fish are a class of vertebrates that live in water bodies. Characteristic features of fish:

• Streamlined shape;
• presence of a heart with two chambers;
• gills for breathing;
• fins and scales covering the body.

The variety of fish is huge: from small tropical species to sharks weighing 12 tons. Some live in the surface waters of the ocean, others live at a depth of more than 2 km, some are freshwater, others inhabit salty waters. These factors influenced the development and evolution of fish, thus forming the variety of fish known to man.

Features of the superclass Bony fish

Characteristic features of bony fish:

• Bony or gill covers - cover the gill slits;
• bone skeleton;
• covered with ganoid scales;
• swim bladder;
• sometimes there are lungs;
• fertilization is only external (caviar);

Bony fish are a diverse group with 22,000 representatives. All reservoirs of the Earth serve as their habitats.

Bone units and their characteristics

Detachment Sturgeon... The spine is mainly made up of cartilage, bone only in the skull. They are characterized by the presence of scales (rather thick scales), located in five rows: one on the back, two on the sides, two in the abdominal region. The cephalic region is elongated, with a small projection that helps in finding food at the bottom (different types of invertebrates). They are found in the Caspian and Black seas, and during spawning they go to the adjacent river mouths. The largest of the Sturgeons is the beluga, weighing about 1000 kg.

Detachment Carps... Almost everyone lives in fresh water, lack of teeth is characteristic. The deficiency is compensated for by the pharyngeal teeth, which serve to grind food. Carps are crucian carp, bream, catfish, as well as piranhas, etc.

Herring... All are marine life, live in large flocks, feed on small crustaceans. The herring species are rounded, flattened from the sides, small gray scales are located on the body. Famous representatives of the order are anchovies, sprats, sprats, etc.

Detachment Codfish... Almost all cod live in the seas, only burbot is freshwater. A distinctive feature of the squad's representatives is the presence of a tendril in the chin area. Cod liver is especially valued as a source of vitamin B.

Kisteperia squad... Science knows only one representative - coelacanth. The body size of latimetry is about 1.5 m. Found in the Indian Ocean. The species disappears within 100 million years and is likely to disappear.

Features of the superclass Cartilaginous

• The skeleton is made up of cartilage tissue;
• there are no covers of the gill slits;
• all representatives have no branchial bladder.

Groups of the Cartilaginous and their characteristics

Shark squad... All fins (first, second dorsal, pectoral, ventral, caudal) are located horizontally, the caudal fin is especially massive. In the head region there are external gill slits, nostrils, the head has an elongated appearance - the rostrum. Sharks breathe through the mouth, also due to the lack of a swim bladder, they constantly move so as not to sink to the bottom.

Fertilization is internal; sharks are characterized by live birth or egg laying. Among the shark-like, there are both small representatives, only 17 cm long, and a whale shark, 12 meters long. Almost all sharks are predators and pose a danger to humans. Some of them feed only on squid or plankton (largemouth, giant, whale).

Stingray squad... Their habitual habitat is the bottom of the sea, their body is flattened in the dorsal region, flat, in the form of a rhombus. The tail section has changed into a plait. The sizes of stingrays range from 4 cm, to large ones, for example the sea devil, with a mass of about 2.5 tons.

For protection from enemies, stingrays can use an electric charge (voltage about 70 W); they can kill or paralyze small animals. Large representatives can be dangerous to humans. Like sharks, stingrays tend to be viviparous, giving birth to offspring from 1-3 to 20-25 cubs.

Lesson topic: Cartilaginous fish

Item: biology

Class: 7

Goals: study the class Cartilaginous fish, their diversity, habitat, behavior, lifestyle.

Lesson Objectives

Tasks:

to learn the main features of cartilaginous fish;

understand the classification;

to identify the traits of adaptability to the environment;

find out the meaning in nature and in human life;

be able to recognize representatives of the Sharks, Stingrays and Chimera-like squads;

develop the ability to observe animals while watching a video clip;

Equipment: table "Cartilaginous fish", presentation.

Planned results:

students should know:

features of the external and internal structure of cartilaginous cells;

the adaptability of cartilaginous fish to environmental conditions;

the role of cartilaginous fish in nature and their importance in human life;

students should be able to:

to recognize representatives of the Sharks, Stingrays, Chimera-like units.

Course lesson a.

1. Organizational moment.

Greetings, message of the topic of the lesson and work plan, mark of absent.

2. Testing knowledge

Written survey

Biological dictation... Insert the missing word.

Fish are animals belonging to Type …… .. and have mastered…. habitat. The body of the fish has …… .. the shape of the body and is divided into sections:…, ……., ……. Outside, the fish skin is covered with ... .. Movement is provided by ... .... Paired fins .... and…, unpaired …………, …………, ………… The horizontal position of fish, turns, movement up and down are carried out by ……………… .. Respiratory organs of fish …… .. The circulatory system of fish… .. The heart of a fish consists of .... cameras:… and…. Through the heart of the fish flows …………… Respiratory system fish is represented by ………… The excretory organs of fish…. are located under the spine.

Compare the answer with the benchmark and mark yourself:

0 errors - "5"

1 error - "4"

2 errors - "3".

3 ... Learning new material.

Formulation of the topic of the lesson and formulation of the educational problem.

Teacher: I’ll give you a riddle now, try to guess who it’s about.

This scary white predator

Looking for food in the ocean.
Sensitive nostrils on the snout:
Blood can smell even a mile away.
Circling around the victim
And the circles are already, already.
Turns up his nose ... Oh my God!
The jaw looks like a trap!
She closed her sharp teeth.
So it hunts ...

Students: Shark.

So, the topic of the lesson: Cartilaginous fish.

Teacher: Let's formulate the objectives of our lesson:

1. to get acquainted with the orders of cartilaginous fish,

2.to learn the features of the structure of cartilaginous fish

3. to learn to recognize by the appearance of cartilaginous fish:

4. learn about the diversity of cartilaginous fish species.

(students try to formulate the purpose of the lesson with the help of the teacher)

Teacher: In the process of work, the table "Groups of Cartilaginous Fishes" is filled in.general characteristics Cartilaginous fish. (Explanation of the teacher with elements of conversation.)

On the desk

– What fish are cartilaginous?

– On the basis of what characteristics are they combined into one group?

– How are cartilaginous fish adapted to their habitat?

– What type of fish are? (chord)

– What subtype? (vertebrates)

Today we will get acquainted with the class of cartilaginous fish.Slide 3

In order to find out the general features of cartilaginous fish, let's watch a movie clip. Slide 4

– What features did you see?

Orders of cartilaginous fish

Related to ancient shell fish

In primitive antiarchs, the whole body was chained in a shell of skin plates;

In carnivorous arthrodirs, the carapace covered only the front part of the body.

Armored - the first jawed fish; their jaws arose from the gill arches, shifted closer to the mouth, and consisted of pointed bony plates.

Shellfish became extinct in the late Devonian.

The cartilaginous fish class includes 3 orders:

Shark squad (250 species)

Squad Stingrays (350 species)

Order Chimera (30 species

1.Shark Squad.

slides 7-13)

Shark variety.

General characteristics of sharks

The respiratory system begins with 5–7 pairs of branchial slits.

In the intestine, a spiral valve stretches along its entire length, increasing the suction surface.

The arterial cone of a two-chambered heart is capable of self-contraction and gives an additional impulse to blood.

The sense organs are represented by the organs of smell, sight, touch( )

Fertilization in almost all cartilaginous fish is internal.

Many of them have a cloaca.

Cartilaginous fish are viviparous or lay eggs.

2.Squad Stingrays.

Explanation of the teacher with elements of conversation ( slides 14-17)

Take a look at the picture. What traits of adaptability to the environment have you seen?

General characteristics of stingrays.

The branchial slits are located on the ventral side

The body is strongly flattened.

Wide pectoral fins grow to the edges of the body and to the head. The caudal fin is thin and its lobes are often reduced. The anal fin is missing.

Pectoral fins are used for movement, flapping them like wings.

Squirt are much better developed than sharks.

Most species are inhabitants of the seabed, which is why their backs have a protective color to match the color of the soil.

Stingrays reproduce by laying encapsulated eggs on the bottom or by live birth.

3. Squad Chimera.

Explanation of the teacher with elements of conversation ( slides 18-20)

General characteristics of chimera.

The jaws are completely fused with the skull.

The gill slits are covered with a skin fold.

There is no cloaca, the anal and urogenital openings are separated from each other.

The naked body, up to 1.5 m long, gradually becoming thinner, passes into a long tail.

They live from the shelf to the great depths of the World Ocean.

Chimeras feed on marine invertebrates and fish.

They have practically no commercial value.

Teacher: Let's check how you filled out the spreadsheet.

(students read the table)

The name of the detachment, the number of species.

4. Fastening.

Choose the correct statements

1) in cartilaginous fish, the gills are closed by cartilaginous lids;

3) most stingrays are near-bottom life;

4) sharks and rays lead a near-bottom lifestyle;

5) all sharks are dangerous to humans;

6) cartilaginous fish have highly developed muscles;

7) cartilaginous fish have a swim bladder;

8) the skin of cartilaginous fish is covered with scales;

9) the body of the rays has a torpedo shape;

10) the color of the rays is patronizing.

6. Reflection.

7. Homework.

1. Section 22.

2. Prepare messages about sharks and rays on the topics: "Manta - sea devil", "Katran - herring shark", "Truth and fiction about sharks."

FISH class cartilaginous(Chondrichthyes) Class FISH cartilaginous (Chondrichthyes).

subclass. Lamellar fish (elasmobranchh) Sharks (selachomorpha) Superorder Skatha (batomorpha) Superorder Fishes, solid-cranial or whole-headed (Holocephali) Subclass: Elasmobranchii - Lamellar fish. This is the order with the greatest diversity of species among sharks. Appeared during the Jurassic period, representatives are found from the intertidal zone to the ocean depths almost everywhere. The external distinguishing features are very variable, but all are characterized by the presence of five gill slits, two dorsal fins (except for the single fin cat shark), and an anal fin. Reproduction methods are also very diverse - there are oviparous, ovoviviparous and viviparous species. Some are characterized by oophagia. Multi-toothed. Appeared in the Triassic period, and represent a detachment of bottom sharks, leading a nocturnal lifestyle. Their external features are a dense body, two spined dorsal fins, and an anal fin. Distributed from the intertidal zone to the continental shelf. All species are oviparous. Polygillus. The detachment is the oldest among the existing sharks - it was formed during the Permian period. Consists of two families, differing in body shape - eel-like in frilled sharks and "traditional" torpedo-shaped in multigill sharks. Both families have six or seven branchial slits, one dorsal fin, and an anal fin. Mostly distributed in the cool depths of the tropics, ovoviviparous. Lam-like. Appeared in the Jurassic period. This order is dominated by pelagic species large sizes... They are torpedo-shaped, with five gill slits, two dorsal fins, and an anal fin. Distributed from the intertidal zone to deep waters ocean, ovoviviparous. Wobbegong-like. Appeared in the Jurassic period. Distributed in warm and tropical seas from intertidal to deep waters. With the exception of the whale shark, all species live on the bottom. They have five gill slits, two dorsal fins, and an anal fin. Among the species are oviparous, ovoviviparous and viviparous. Some also have oophagia.

Saw-shaped. Perhaps the most easily identifiable unit. It appeared during the Jurassic period. Sharks of this order are distinguished by a specific long, sawtooth muzzle, dotted with teeth, as well as the absence of an anal fin, two dorsal fins and large spiracles. They live at the bottom, ovoviviparous. Katraniform. Appeared in the Jurassic period. This order is widespread and found all over the world, including - the only shark - in latitudes close to the poles. They live at great depths. Representatives of the detachment have a torpedo-shaped body, five gill slits, two dorsal fins, and an anal fin is missing. Ovoviviparous.

Squat-like. Appeared in the Triassic period. The habitat is usually the silt or sand of the continental shelf and intertidal zone in cool temperatures, as well as deeper areas in tropical waters. Sharks of this order are distinguished by a wide flattened body, a short muzzle, five gill slits, large pectoral and pelvic fins, and the absence of an anal fin. Outwardly, they resemble stingrays, but the difference is that the gills open on the sides of the body, and not below, and wide pectoral fins are clearly visible, clearly separated from the head. All species are ovoviviparous Order: Carcharhiniformes Compagno - Carhariniformes Order: Heterodontiformes Berg - Mottoid Order: Hexanchiformes Buen - Polygillaceous Order: Lamniformes - Lamiformes Order: Orectolobiformes Compagno-like Squid-like Squid-like Squid-shaped

52 taxonomy of cartilaginous fish, a variety of rays. Class FISH CARRYING (Chondrichthyes).

subclass. Elasmobranchs (elasmobranchh) Stingray rays (Anacanthobatidae) Rhombus rays (Rajidae) Rhinidae Rhinobatidae rays (Rhinobatidae) Shark-tailed rays (Rhynchobatidae)

Representatives of this order have a strongly flattened rhomboid body, on the pelvic cartilages there are peculiar outgrowths and traces of gill folds in the spigots. In the skates of this order, tail spines are absent, and the caudal fin is greatly reduced. They are typically benthic. Also, some rays of this order have large spines along the middle of the body. The color of individuals depends on the color of the soil of the environment in which they live. Stingrays are predominantly nocturnal, and during the day they are not very active and burrow into the ground, leaving only their eyes on the surface. They predominantly live in coastal waters, although deep-sea rays also exist.

Today this order is the most numerous and includes about 200 species of rays. Distributed everywhere, however, the greatest diversity is reached in the polar regions and regions with a temperate climate. V Russian waters the order is represented by only one family - the family of rhomboid rays (Rajidae). They feed on small fish and benthic invertebrates. Reproduction takes place by laying cornea-coated eggs.

53 question The main features of the organization. Cartilaginous fish, characteristics of lamellar and whole-headed fish. Lamellibranch * (Lamellibranchiata) - a class of molluscs type. Characteristics of P.: the body is usually quite symmetrical, almost always laterally compressed, laterally covered by two large mantle lobes, between which there is a large mantle cavity enclosing the lower body and leg of the animal, two gills attached to the sides of the body, and 2 pairs of triangular oral lobes; a shell of two lateral valves connected to each other at the dorsal edge and brought together by means of 1 or 2 muscles extending from one valve to the other; detached head, cephalic tentacles, pharynx, jaws and radula are absent; paired kidneys and gonads; a heart with 2 atria; dioecious or hermaphrodites, exclusively aquatic animals, freshwater and marine, mostly free, less often, in adulthood, attached. Despite the considerable variety in appearance and structure, P. represent a very natural group, easily distinguishable from other representatives of the mollusc type. In the vast majority of P., the body is quite pronounced two-sided symmetry; less often, symmetry is disturbed by the unequal development of the right and left halves due to the fact that an adult animal is either attached to underwater objects (usually grown) on one side (for example, an oyster), or usually lies on one side (for example, some species scallop - Pecten); at the same time, the valves differ in size, shape, thickness, color, sculpture, and internal organs also represent a more or less significant deviation from symmetry. The shell valves are for the most part large and can completely cover the body of the animal, but sometimes they are very small (for example, in a woodworm; see Molluscs, corresponding fig.). In addition to the shell valves, the mantle can secrete lime deposits in the form of additional plates or a layer lining the channels in which the mollusk (woodworm) lives, or in the form of a tube that replaces the shell, while the minor valves of the latter merge with the tube (in Kropilets - see. , or watering jars - Aspergillum). On the dorsal edge of the valve, the so-called. a strand (ligamentum), which, when the muscles contract, that is, the shell is closed, is compressed, and when the muscles are relaxed, it pushes the flaps. In addition to the strand, on the dorsal edge of the valves of some P. there is a lock - more or less developed protrusions and depressions of the inner surface of the valves, the arrangement and shape of which are such that when the valves are closed, the protrusions of one enter the depressions of the other, facilitating the tight connection of the valves of the closed shell. On the inner surface of the valves, a line is visible corresponding to the edge of the mantle, and the attachment points of 1 or 2 strong muscles bringing the valves closer together. Adjacent valves are not always completely in contact: they often leave a more or less significant opening (gaping shells) open. Both lobes of the mantle can be completely free at the front, lower and rear edges, or be spliced ​​together over a more or less significant extent in one, two, rarely three places. Due to the fusion or sometimes close adhesion of the mantle blades to each other in known places, the entrance to the mantle cavity splits into 2-4 sections: through the rearmost one, water that washed the gills is removed, along with feces and excretion products, through the next, water enters the mantle cavity, a leg extends through the front opening; behind the latter, there is occasionally another small hole, probably corresponding to the byssus, if there are only two holes, then water is discharged through the back, water is introduced through the front, and the leg with the byssus extends. The edge of the mantle can be simple or thickened with special sense organs (papillae, tentacles, eyes). The edges of both posterior openings are often lengthened, forming two tubular siphons: through one (lower) water enters (gill siphon), through the other (upper) it exits (anal siphon); siphons can be many times the length of the shell; sometimes they are more or less connected to each other (see. acc. Fig.) The body of the animal, devoid of a separate head section, ends from below in a muscular, more or less strongly developed, but sometimes rudimentary leg; most often the leg is conical or wedge-shaped, but in some P. of the most primitive structure, the leg is equipped with an extended flat sole (in Nucula, Leda, Yoldia). Many P. have a special gland in the leg that secretes dense filaments similar to horny ones - the so-called Byssus, with which the animal can temporarily attach itself to underwater objects. The order True lamellar-gill family includes more than one hundred families and is divided into four suborders: Split-toothed (Schizodonta), Multi-toothed (Heterodonta) - the largest in terms of the number of families, genera and species, Adapedonta and Anomalodesmata. ) Possessing a number of unique features, representatives of this subclass of fish, in addition, in the most bizarre way combine the features of the plate-gill (Elasmobranchii) and bony fish (Osteichthyes). It is no coincidence that the great Linnaeus gave one of the genera the name "Chimera". With lamellar gills (selachia), they are, first of all, related by the presence of paired copulatory organs (pterygopodia) in males; the ability of females to lay large eggs enclosed in horn capsules; the presence in the external skeleton of placoid scales ("skin teeth") and the complete absence of ossification of the internal cartilaginous skeleton, some elements of which are sometimes strengthened due to calcification (should not be mixed with ossification). In addition, in the heart of modern fused cranials, as well as of lamellibranchs, there is an arterial cone, equipped with three rows of valves; a spiral valve passes through the intestine; large nostrils are brought close to the transverse mouth and communicate with its posterior corners with the help of furrows dissecting the upper lip; the outer lobes of the fins are supported by a large number of thin elastoidin filaments (elastotrichia), while in teleost fishes their homologous fin rays are replaced by bony rays (lepidotrichia); the fleshy lips are supported by labial cartilage, and, like the laminobranchs, the brain and heart are arranged and the swim bladder is initially absent.

Question 54 General characteristics of the Bone class, the system up to subclasses. The bony fish class represents the largest superclass of fish. It includes about 20,000 species. This class is common in almost all water bodies of the surrounding world. The living conditions of bony fish are very diverse, which explains the richness of this group of species and their diversity. The Osteichtyes class consists of a wide variety of fish species. Their scales are ctenoid or cycloid, as well as serrated or smooth, depending on the shape. The class of bony fish is several times more diverse than the class of cartilaginous fish. The skeleton is predominantly bony. The appearance of the skeleton is possible in two main ways. The initial type of ossification is the integumentary or cutaneous bones. Embryonic ossification occurs in the connective layer of the skin, regardless of the presence of cartilaginous components of the skeleton, since it is only attached to them. Based on the above-described features, the development of the integumentary bone often has the form of plates. In addition to the presence of integumentary bones, the skeleton of fish has cartilaginous or chondral bones. Their occurrence occurs in the embryonic period due to the replacement of cartilage with bone substance that produces osteoblasts. As chondral bones appear, the skeleton of fish gradually ossifies, which makes its own adjustments to the general structure of the skeleton. Due to the formation of integumentary ossifications, new elements of the skeleton appear, which significantly complicates its general structure. There is a reduction in the intercostal septa of the respiratory apparatus. The gill petals are located directly outside the branchial apparatus. Most species of the bony fish class have a swim bladder. Almost all species of fish of this class reproduce by external fertilization. The laid eggs are small, without horn-like shells. A negligible number of bone-class fish species have live-born offspring. The classification of bony fish is so complicated that at present there are several views on the taxonomy of this group. Subclass Ray-finned fish (Actinopterygii) Subclass Lobster-finned fish (Sarcopterygii).

55. Characteristics of the Blade: features of the organization, their origin and evolution.

Lobe-finned (lat. Sarcopterygii) or choanic - a class of bony fish. The axial skeleton is based on an elastic chord. Known from the early Devonian (300-400 million years ago), they combine both archaic and progressive features. The superorders are lung-finned and cross-finned superorders. Lobe-finned fish (in contrast to ray-finned fish) have moved to living in inland water bodies, their outgrowth of the esophagus turns into a lung, the leading analyzer is the sense of smell, and compared to other fish, the brain changes. The scales are cosmoid or bony. Throughout life, the notochord is preserved, surrounded by a dense connective tissue fibrous-elastic sheath. The upper and lower arches develop, and in the caudal region there are sometimes underdeveloped vertebral bodies (in some fossil groups they were better developed than in living species). The skull is amphilistic or autostylish. Scaly bone is present among the integumentary bones of the skull. The tail is heterocercal (fossil) or dificercal. Paired fins with a fleshy blade covered with scales at the base; their skeleton is of a bead type. There is a cone arteriosus in the heart. The intestine has a spiral valve and opens into the cloaca. As outgrowths of the ventral side of the initial part of the esophagus, one or two bubbles are formed, which perform the function of the lungs. Known from the Lower Devonian. Superorder cross-finned fishes (CROSSOPTER YGIMORPHA). The cerebral skull is divided into two parts - the olfactory and the cerebral itself, movably connected to each other. The degree of ossification of the skull varies, integumentary ossification is developed. The skull is amphistilic; in some species, a transition to autostyly is planned. The secondary jaws are well developed, the teeth are strong and sharp. There may be vertebral bodies with a shortened central axis and a well-developed basal element at the base. They occur from the Lower Devonian in the form of several, already clearly limited groups. Freshwater predators that have repeatedly entered the seas.

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