Marry

Lungfish. Living fossils. Lungfishes Characteristics of lobe-finned fishes

Lungfishes and their

DISTRIBUTION IN NATURE;

CHARACTERISTICS OF LACE-FISHES;

GENERAL CHARACTERISTICS OF THE CRANIALS;

BONE FISH CLASSIFICATION SYSTEM.

individual work

biology student

groups 4120-2(b)

Menadiev Ramazan Ismetovich

Zaporizhia 2012

Animal Kingdom

Type: Chordata, chordata

Subphylum Vertebrates, vertebrata

Superclass: Pisces, pisces

Class: Bony fishes, osteichtyes

Superorder: Lungfishes, dipnoi

Lungfish are a small ancient and very unique group of freshwater fish, combining primitive characteristics with features of high specialization for life in oxygen-depleted reservoirs. In modern representatives, most of the skeleton remains cartilaginous throughout life. A well-developed notochord is preserved. The spinal column is represented by the rudiments of the upper and lower vertebral arches. The skull is basically cartilaginous with a few integumentary bones and bony dental plates. Like cartilaginous fish, the intestine has a spiral valve, and the heart has a pulsating cone arteriosus. These are primitive features of the organization. Along with this, in lungfishes the quadrate palatocartilage grows directly to the skull (autostyly). The caudal fin merges with the dorsal and anal (dificercal). The paired limbs have a wide, leathery blade. The name Lungfish speaks about the most important feature - the presence of gill and pulmonary respiration. 1 or 2 bladders function as pulmonary respiratory organs, opening on the abdominal side of the esophagus. These formations are not homologous to the swim bladder of bony fish. The nostrils are through, lead into the oral cavity and serve for pulmonary breathing. Blood enters the lungs through special vessels extending from the 4th pair of gill arteries. The vessels are homologous to the pulmonary arteries. From the “lungs” come the vessels that carry blood to the heart (homologues of the pulmonary veins). The progressive features of lungfish also include the strong development of the forebrain. The genitourinary system is close to the genitourinary system of cartilaginous fish and amphibians.

Axial skeleton lungfish - fish largely retain primitive features: there are no vertebral bodies, the cartilaginous bases of the upper and lower arches sit directly on the notochord, which is well preserved throughout life. The skull, along with ancient features, is characterized by a peculiar specialization. In the cartilaginous cranium (neurocranpum), only one pair of replacement bones (lateral occipital) develops. Available a large number of peculiar covering bones of the skull. The palatoquadrate cartilage fuses with the base of the skull. On the vomer, pterygopalatine bones and lower jaws sit bone chewing dental plates, formed from the fusion of numerous small teeth and very similar to the cranial plates (4 plates on the upper jaw and 2 on the lower jaw).

Cartilaginous skeleton paired fins are supported by almost the entire fin blade, except for its outer edge, where it is supported by thin skin rays. This peculiar internal skeleton consists of a long articulated central axis, which in the horned teeth (Ceratodidae) carries two rows of lateral articulated cartilaginous elements, while in the squamate (family Lepidosirenidae) it does not have these appendages or carries their rudiments. Internal skeleton The fins are connected to the belt by only one main (basal) segment of the central axis and in this respect are to a certain extent similar to the limbs of terrestrial vertebrates. Unpaired fins, dorsal and anal, completely merge with the caudal fin. The latter is symmetrical and has a diphycercal structure (in many fossil lungfishes the tail was unequally lobed - heterocercal). The scales of ancient forms were of the “cosmoid” type; in modern lungfishes the upper enamel layer and dentin have been lost. The heart has a conus arteriosus; the intestine is equipped with a spiral valve - these are primitive signs. The genitourinary apparatus is similar to that of shark fish and amphibians: there is a common excretory opening (cloaca).

Despite the fact that according to modern views lungfish represent a lateral branch of the main “trunk” of aquatic vertebrates, interest in this amazing group of animals does not wane, since through its example one can trace the evolutionary attempts of nature to make the transition of vertebrates from aquatic to terrestrial existence and from gill to pulmonary respiration.

3 orders: Horntoothed (ceratodiformes ) – 1 type; Squamate, Dipulmonate, (Lepidosirenidae) – 5 species. Dipteriformes ( Dipteridiformes) - extinct.

Order Dipteriformes (Dipteridiformes). This includes extinct lungfish from the Middle and Upper Devonian, distributed throughout fresh water bodies around the globe. By the end Paleozoic era died out. They are characterized by cosmoid scales, varying degrees of ossification of the brain skull and a wide variety of integumentary bones, reduction of secondary jaws, the presence in some species of conical teeth that are not fused into dental plates, the presence of rudiments of vertebral bodies, and independence of unpaired fins. Apparently, they lived in reservoirs rich in aquatic vegetation, feeding on sedentary animals and plants.

Paleozoic forms probably already had pulmonary respiration and, at least in some species, the ability to fall into a state of peculiar hibernation when water bodies dried up (fossil “cocoons” were found in Permian deposits).

Order Horntoothed, or One-lunged (Ceratcdiformes). The brain skull is cartilaginous, with minor ossifications. Covering bones are few in number. There are no secondary jaws. Dental plates with a small number of thick, slightly tuberculate ridges. The paired biserial fins are well developed. There is only one lung with a weakly cellular inner wall. The scales are bony, large. Apparently, they separated from dipteridia at the end of the Devonian, but the most ancient remains are known only from the Lower Triassic. In the Mesozoic era they were found in all continental bodies of water; Many fossil species have been described.

Now there is only one species living - horntooth - Neoceratodus forsteri. It is found in a small area of Western Australia. Reaches a length of up to 1.5 m and a weight of over 10 kg. Lives in slow-flowing rivers overgrown with aquatic and emergent vegetation. The period of drought, when the rivers become shallow, is experienced in the preserved pits with water. Periodically, every 40-50 minutes, it floats up, noisily exhales air from its lungs and, after inhaling, sinks to the bottom. When the pit dries out completely it dies.

It feeds by moving slowly near the bottom and eating invertebrates; the intestines usually contain a lot of finely ground plant residues, but it is believed that vegetation is poorly digested. Large eggs, up to 6-7 mm in diameter, are deposited on aquatic plants. After 10-12 days, the fry hatches with a large yolk sac. It breathes through gills and usually lies on the bottom, only occasionally moving a short distance. After the yolk sac is reabsorbed, they become more mobile and stay in the creeks, feeding on filamentous algae. The pectoral fins appear on the 14th day after hatching (probably from this time the lung begins to function); abdominal - after about 2.5 months. Rogozubov were vigorously exterminated due to delicious meat; Fishing was made easier by the low mobility of the fish. Now the horntooths are protected; Attempts are being made to re-acclimatize them in other water bodies of Australia.

Order Dipulmoniformes(Lepidosireniformes). The brain skull is cartilaginous, with minor ossifications. Covering bones are few in number. There are no secondary jaws. Dental plates with sharp cutting ridges. The bones of the operculum are noticeably reduced. The paired fins look like long tentacles; their skeleton is formed only by a dissected central axis. Small cycloid scales are deeply embedded in the skin. The lungs are paired, weakly cellular. Development with metamorphosis: the larvae develop cutaneous external gills, which disappear with the onset of lung function. Like monopulmonates, they apparently separated from some dipteridians at the end of the Devonian - the beginning of the Carboniferous period. A few fossils have been found in the Permian sediments of the United States and on the Russian Platform.

Protopterus.

When the reservoir dries out, all species burrow into the ground, surviving the dry period. For example, when the water level drops to 5-10 cm, Protopterus digs a hole. The soil is captured by the mouth, crushed and thrown out through the gill slits. Having dug a vertical passage, the fish expands its end into the chamber in which it is located, sharply bending its body and sticking its head up. When the water level drops, the soil closes the entrance to the hole, and the fish, using head movements from the inside, seals this plug. In large fish, the chamber is located at a depth of up to half a meter. Due to the hardening of the skin mucus around the fish, a cocoon that fits tightly to the skin is formed (the thickness of its walls is only 0.05-0.06 mm); and the upper part of the cocoon, a thin tube is formed through which air penetrates to the fish’s head. The fish remains in this state until the next rainy period, about 6-9 months (in an experiment in laboratory conditions, the fish hibernated for over four years and woke up safely). During hibernation, the metabolic rate sharply decreases. Apparently, not only fat, but also muscle serves as an energy reserve. During 6 months of hibernation, the fish loses up to 20% of its original mass. During the period of active life, the products of nitrogen metabolism are excreted from the body mainly in the form of ammonia, and when entering torpor they are converted into urea, which is less toxic compared to ammonia, and are not excreted, but accumulate, making up 1-2% of the fish’s mass by the end of hibernation; The mechanisms that ensure the body's resistance to such high concentrations of urea have not yet been elucidated. When reservoirs are filled during the rainy season, the soil gradually becomes wet, water fills the air chamber, and the fish, having broken through the cocoon, sticks its head out, inhaling air every 5-10 minutes, and after a few hours, when the water covers the bottom of the reservoir, leaves the hole. Soon the urea is excreted through the gills and kidneys. During hibernation, the formation of reproductive products occurs. A month and a half after emerging from hibernation, reproduction begins. At the bottom of the reservoir, among thickets of vegetation, the male digs a horseshoe-shaped hole with two entrances, at the bottom of which the female lays up to 5 thousand eggs with a diameter of 3-4 mm. After 7-9 days, the eggs hatch into larvae with a large yolk sac and 4 pairs of feathery external gills. Using a special cement gland, the larvae attach to the walls of the nesting hole. The male stays near the nest throughout the entire incubation period and the first weeks of the larvae’s life and actively defends it, even rushing at an approaching person. After 3-4 weeks, the yolk sac is completely absorbed, a pair of external gills are reduced (the rest are absorbed more slowly), and the larva leaves the burrow, beginning to actively feed. If necessary, it rises to the surface to swallow atmospheric air. The larvae acquire the ability to burrow into the ground during drought, form a cocoon and hibernate at a length of 4-5 cm. 2-3 weeks after emerging from hibernation (after filling the reservoir with water), the fish begin to reproduce. The male digs a vertical burrow, sometimes bending horizontally towards the end. Some burrows reach 1.5 m in length and 15-20 cm in width. The fish drags leaves and grass to the end of the hole, onto which the female lays eggs with a diameter of 6-7 mm. The male remains in the hole, guarding the eggs and hatched young. At this time, branching leathery outgrowths 5-8 cm long, abundantly supplied with capillaries, develop on its ventral fins. It was assumed that these outgrowths help saturate the water in the nesting chamber with oxygen. Other ichthyologists believe that these outgrowths compensate for the inability to use pulmonary respiration in the burrow. After the breeding season, these growths resolve. The mucus secreted by the male's skin has a coagulating effect and clears turbidity from the nest water. The larvae hatched from the eggs have 4 pairs of highly branched external gills and a cement gland, with the help of which they are attached to the walls of the nest. About a month and a half after hatching (at a length of 4-5 cm), the larvae leave the burrow, begin to actively feed and can breathe with their lungs, while the external gills dissolve.

The areas of distribution of these relict forms - South America, tropical Africa and Australia - indicate the great antiquity of the group.

When, during a six-month drought, Lake Chad in Africa reduces its area by almost one third and the muddy bottom is exposed, local residents go fishing, taking with them... hoes. They look for mounds on the dry bottom that resemble molehills, and from each they dig out a clay capsule with a fish folded in half, like a hairpin.

This fish is called Protopterus ( Protopterus) and belongs to subclass 1 of lungfishes ( Dipnoi). In addition to the usual gills for fish, representatives of this group also have one or two lungs - a modified swim bladder, through the walls of which gas exchange occurs, entwined with capillaries. The fish capture atmospheric air for breathing through their mouths, rising to the surface. And in their atrium there is an incomplete septum, which continues in the ventricle. Venous blood coming from the organs of the body enters the right half of the atrium and the right half of the ventricle, and blood coming from the lung enters the left side of the heart. Then the oxygenated “pulmonary” blood enters mainly those vessels that lead through the gills to the head and body organs, and the blood from the right side of the heart, also passing through the gills, largely enters the vessel leading to the lung. And although poor and oxygen-rich blood partially mix both in the heart and in the vessels, we can still talk about the rudiments of two circulatory circles in lungfish.

Lungfishes are a very ancient group. Their remains are found in sediments of the Devonian period of the Paleozoic era. For a long time, lungfish were known only from such fossilized remains, and only in 1835 was it established that the protoptera living in Africa was a lungfish. In total, as it turned out, representatives of six species of this group have survived to this day: the Australian cattail from the order of monopulmonates, the American lepidoptera - a representative of the order of bipulmonates, and four species of the African genus Protopterus, also from the order Dipulmonates. All of them, like, apparently, their ancestors, are freshwater fish.

Australian Horntooth ( Neoceratodus forsteri) is found in a very small area - in the Burnett and Mary river basins in north-eastern Australia. This big fish with a body length of up to 175 cm and a weight of over 10 kg. The massive body of the horntooth is laterally compressed and covered with very large scales, and its fleshy paired fins resemble flippers. The horntooth is painted in uniform tones - from reddish-brown to bluish-gray, the belly is light.

This fish lives in slow-flowing rivers, heavily overgrown with aquatic and surface vegetation. Every 40 - 50 minutes, the cattail emerges and noisily exhales air from the lung, while emitting a characteristic groaning-grunting sound that spreads far across the surrounding area. After inhaling, the fish sinks to the bottom again.

The horntooth spends most of its time at the bottom of deep pools, where it lies on its belly or stands, leaning on its flipper-like fins and tail. In search of food - various invertebrates - it slowly crawls, and sometimes “walks”, relying on the same paired fins. It swims slowly, and only when startled does it use its powerful tail and show the ability to move quickly.

The cattail survives the period of drought, when the rivers become shallow, in preserved pits with water. When fish die in overheated stagnant and practically oxygen-deprived water, and the water itself turns into a fetid slurry as a result of putrefactive processes, the cattail remains alive thanks to its pulmonary respiration. But if the water dries out completely, these fish still die, since, unlike their African and South American relatives, they cannot hibernate.

The horntooth spawns during the rainy season, when the rivers swell and the water in them is well aerated. The fish lays large eggs, up to 6–7 mm in diameter, on aquatic plants. After 10–12 days, the larvae hatch, which lie on the bottom until the yolk sac is absorbed, only occasionally moving a short distance. On the 14th day after hatching, the fry develop pectoral fins, and from this time the lung probably begins to function.

The cattail has tasty meat and is very easy to catch. As a result, the number of these fish has greatly decreased. Now the horned teeth are under protection and attempts are being made to acclimatize them in other bodies of water in Australia.

The history of one of the most famous zoological hoaxes is connected with the horntooth. In August 1872, the director of the Brisbane Museum was touring north-eastern Australia, and one day he was informed that a breakfast had been prepared in his honor, for which the natives had supplied very rare fish, caught by them 8-10 miles from the feast. And indeed, the director saw a fish of a very strange appearance: a long, massive body was covered with scales, the fins looked like flippers, and the snout resembled a duck’s beak. The scientist made drawings of this unusual creature, and after returning he handed them over to F. De Castelnau, a leading Australian ichthyologist. Castelnau was quick to describe a new genus and species of fish from these drawings - Ompax spatuloides. A rather heated discussion followed about family ties a new species and its place in the classification system. There were many reasons for disputes, since in the description Ompax much remained unclear and there was no information on anatomy at all. Attempts to obtain a new specimen were unsuccessful. There were skeptics who expressed doubts about the existence of this animal. Still mysterious Ompax spatuloides for almost 60 years continued to be mentioned in all reference books and reports on Australian fauna. The mystery was resolved unexpectedly. In 1930, a note appeared in the Sydney Bulletin, the author of which wished to remain anonymous. This note reported that an innocent joke was played on the simple-minded director of the Brisbane Museum, since the “Ompax” served to him was prepared from the tail of an eel, the body of a mullet, the head and pectoral fins of a horntooth and the snout of a platypus. From above, this entire ingenious gastronomic structure was skillfully covered with scales of the same horned tooth...

African lungfishes - protopters - have thread-like paired fins. The largest of the four species is large protopter(Protopterus aethiopicus) can reach a length of more than 1.5 m, and the usual length small protopter(P.amphibius) – about 30 cm.

These fish swim, bending their bodies like snakes like eels. And along the bottom, with the help of their thread-like fins, they move like newts. The skin of these fins contains numerous taste buds - as soon as the fin touches an edible object, the fish turns around and grabs the prey. From time to time, the protopters rise to the surface, swallowing atmospheric air through their nostrils.

Protoptera live in Central Africa, in lakes and rivers flowing through swampy areas that are subject to annual flooding and dry out during the dry season. When the reservoir dries out, when the water level drops to 5–10 cm, the protopters begin to dig holes. The fish grabs the soil with its mouth, crushes it and throws it out through the gill slits. Having dug a vertical entrance, the protopter makes a chamber at its end, in which it is placed, bending its body and sticking its head up. While the water has not yet dried, the fish rises from time to time to take a breath of air. When the film of drying water reaches the upper edge of the liquid silt lining the bottom of the reservoir, part of this silt is sucked into the hole and clogs the exit. After this, the protopter no longer appears on the surface. Before the cork completely dries, the fish, poking its snout into it, compacts it from below and slightly lifts it in the form of a cap. When dry, such a cap becomes porous and allows enough air to pass through to support the life of a sleeping fish. As soon as the cap hardens, the water in the burrow becomes viscous due to the abundance of mucus secreted by the protopter. As the soil dries, the water level in the hole drops, and eventually the vertical passage turns into an air chamber, and the fish, bent in half, freezes in the lower, expanded part of the hole. A mucous cocoon tightly adjacent to the skin is formed around it, in the upper part of which there is a thin passage through which air penetrates to the head. In this state, the protopter awaits the next rainy period, which occurs in 6–9 months. In laboratory conditions, the protopters were kept in hibernation for over four years, and at the end of the experiment they woke up safely.

During hibernation, the protoptera's metabolic rate sharply decreases, but nevertheless, over 6 months the fish loses up to 20% of its original mass. Since energy is supplied to the body through the breakdown of not fat reserves, but mainly muscle tissue, nitrogen metabolism products accumulate in the fish’s body. During the active period, they are excreted primarily in the form of ammonia, but during hibernation, ammonia is converted into less toxic urea, the amount of which in the tissues by the end of hibernation can be 1–2% of the fish’s weight. The mechanisms that ensure the body's resistance to such high concentrations of urea have not yet been elucidated.

When reservoirs are filled with the beginning of the rainy season, the soil gradually becomes wet, water fills the air chamber, and the protopter, having broken through the cocoon, begins to periodically stick its head out and inhale atmospheric air. When water covers the bottom of the reservoir, the protopter leaves the burrow. Soon, urea is eliminated from his body through the gills and kidneys.

A month and a half after emerging from hibernation, protopterans begin to reproduce. In this case, the male digs a special spawning hole at the bottom of the reservoir, among thickets of vegetation, and lures one or several females there, each of which lays up to 5 thousand eggs with a diameter of 3–4 mm. After 7–9 days, larvae appear with a large yolk sac and 4 pairs of feathery external gills. Using a special cement gland, the larvae attach to the walls of the nesting hole.

After 3–4 weeks, the yolk sac is completely absorbed, the fry begin to actively feed and leave the hole. At the same time, they lose one pair of external gills, and the remaining two or three pairs can remain for many months. In the small protoptera, three pairs of external gills are retained until the fish reaches the size of an adult.

Having left the spawning hole, the protoptera fry swim only next to it for some time, hiding there at the slightest danger. All this time, the male is near the nest and actively protects it, even rushing at an approaching person.

Protopter dark ( P. dolloi), found in the Congo and Ogowe river basins, lives in swampy areas where the layer underground water persists during the dry season. When surface waters begin to decrease in summer, this fish, like its relatives, buries itself in the bottom mud, but digs down to a layer of liquid silt and underground water. Having settled there, the dark protoptera spends the dry season without creating a cocoon and rising up from time to time to breathe fresh air.

The burrow of the dark protopter begins with an inclined passage, the expanded part of which serves as a spawning chamber for fish. According to local fishermen, such holes, if they are not destroyed by floods, serve the fish for five to ten years. Preparing the hole for spawning, the male builds up a mud mound around it year after year, which eventually reaches 0.5–1 m in height.

Protopters have attracted the attention of scientists involved in the creation of sleeping pills. English and Swedish biochemists tried to isolate “hypnotic” substances from the body of hibernating animals, including from the body of the protoptera. When an extract from the brains of sleeping fish was injected into the bloodstream of laboratory rats, their body temperature began to drop rapidly, and they fell asleep as quickly as if they were fainting. The sleep lasted 18 hours. When the rats woke up, there were no signs that they were in artificial sleep, we could not find them. The extract obtained from the brains of awake protopters did not cause any effects in rats.

American scalefish ( Lepidosiren paradoxa), or lepidosiren,- a representative of lungfishes living in the Amazon basin. The body length of this fish reaches 1.2 m. The paired fins are short. Lepidosirens live mainly in temporary reservoirs, filled with water during rains and floods, and feed on a variety of animal foods, mainly mollusks. Maybe they eat plants too.

When the reservoir begins to dry up, lepidosiren digs a hole at the bottom, in which it settles in the same way as protopters, and clogs the entrance with a plug of soil. This fish does not form a cocoon - the body of the sleeping lepidosiren is surrounded by mucus moistened by groundwater. Unlike protopters, the basis of energy metabolism during the hibernation period in lepidoptera is stored fat reserves.

2–3 weeks after the new flooding of the reservoir, lepidosirens begin to reproduce. The male digs a vertical burrow, sometimes bending horizontally towards the end. Some burrows reach 1.5 m in length and 15–20 cm in width. The fish drags leaves and grass to the end of the hole, onto which the female lays eggs with a diameter of 6–7 mm. The male remains in the hole, guarding the eggs and hatched young. The mucus secreted by its skin has a coagulating effect and purifies the water in the burrow from turbidity. In addition, at this time, branching skin outgrowths, 5–8 cm long, abundantly supplied with capillaries, develop on its ventral fins. Some ichthyologists believe that during the period of caring for offspring, lepidosirene does not use pulmonary respiration and these outgrowths serve as additional external gills. There is also an opposite point of view - having risen to the surface and taking a breath of fresh air, the male lepidosiren returns to the hole and, through the capillaries on the outgrowths, releases part of the oxygen into the water in which eggs and larvae develop. Be that as it may, after the breeding period these growths resolve.

The larvae hatched from the eggs have 4 pairs of highly branched external gills and a cement gland, with the help of which they attach to the walls of the nest. About a month and a half after hatching, when the fry reach a length of 4–5 cm, they begin to breathe using the lungs, and the external gills dissolve. At this time, the lepidosiren fry leave the hole.

The local population appreciates the tasty meat of lepidoseren and intensively exterminates these fish.

Literature

Life of animals. Volume 4, part 1. Pisces. – M.: Education, 1971.
Science and life; 1973, no. 1; 1977, no. 8.
Naumov N.P., Kartashev N.N. Zoology of vertebrates. Part 1. Lower chordates, jawless fish, amphibians: A textbook for biologists. specialist. univ. – M.: graduate School, 1979.

T.N. Petrina

1 According to other ideas, lungfish ( Dipneustomorpha) – superorder in the subclass lobe-finned ( Sarcopterygii).
2 In most fish, the nostrils are blindly closed, but in lungfish they are connected to the oral cavity.

This subclass includes only 3 modern representatives who lead a sedentary lifestyle in fresh waters and have the ability to breathe not only oxygen dissolved in water, but also atmospheric air using the lungs.

Lungfishes reach 1-2 m in length and have an elongated body covered with imbricated cycloid bone scales. They do not have separate dorsal and anal fins: they merge with a large diphycercal caudal fin. The paired fins have the shape of either wide blades or long strands.

The notochord remains throughout life, and the vertebral bodies do not develop, but there are cartilaginous upper and lower arches and ribs. The skull, unlike all other bony fish, is autostylous, cartilaginous, but complicated by chondral and integumentary bones. Secondary jaws (premaxillary, maxillary and dentary bones) are absent. The gill arches, including four or five pairs, are cartilaginous. The shoulder girdle is well developed, cartilaginous, but covered with overhead bones. The pelvic girdle is in the form of an unpaired cartilaginous plate. The paired fins are cartilaginous, like a biserial archipterygium. In a typical form, biserial fins are found in ceratodes, while in two other modern lungfishes the fins have the form of filamentous appendages. The exoskeleton of both paired and unpaired fins consists of dissected horny rays.

The brain is characterized by a significant size of the forebrain, which is divided into twohemispheres are not only outside, but also inside, so that there are two independent lateral ventricles. The midbrain is relatively small. The cerebellum is extremely poorly developed, which is associated with the low mobility of lungfish.

(according to Goodrich):

1 - pelvis, 2 - basalia, 3 - radials

(according to Parker):

1-4 - afferent branchial arteries, 5 - 8 - efferent branchial arteries, 9 - pulmonary arteries, 10 - conus arteriosus, 11 - left atrium, 12 - right atrium, 13 - ventricle of the heart, 14 - jugular veins, 15 - brachial veins , 16 - subscapular veins, 17 - left posterior cardinal vein, 18 - pulmonary vein, 19 - posterior pudendal vein, 20 - dorsal aorta, 21 - Cuvier's ducts

The teeth are very peculiar; they are fused into plates, the sharp peaks of which are directed forward. A pair of such teeth is placed on the roof of the oral cavity, and the ceratod also has a pair of flat teeth on the lower jaw. The intestine is equipped with a well-developed spiral valve and opens into the cloaca.

Along with the gills, there are lungs that communicate with the ventral side of the esophagus and have a cellular structure of the inner wall. There is no swim bladder. In connection with the development of pulmonary breathing, in addition to the external nostrils, there are also internal nostrils.

The circulatory system is distinguished by the following features: 1) the pulmonary artery departs from the pair of efferent gill arteries closest to the heart, while the pulmonary veins depart from the lung and flow into the left half of the atrium; when the gills are functioning, already oxidized blood enters the pulmonary arteries, so that the lung is inactive, but when the gills do not function due to a lack of oxygen in the water, then venous blood enters the lung; 2) the atrium is subdivided incomplete septum into two halves (right and left), and the arterial cone is equipped with a longitudinal valve dividing it into two parts; 3) along with the posterior cardinal veins, there is a posterior vena cava into which the renal veins flow. Thus, the venous system of lungfish occupies an intermediate position between the circulatory system of aquatic and terrestrial vertebrates.

The genitourinary system is generally structured like the genitourinary systems of cartilaginous fish, and the oviducts (Müllerian canals) open into the body cavity, but the efferent ducts of the testes may be absent. Then the seed comes out, apparently through the abdominal pores. In addition, male lungfish lack copulatory organs; external insemination. The eggs are quite large, about 7 mm in diameter, surrounded by a gelatinous membrane and resemble amphibian eggs; deposited among vegetation and often sinks to the bottom.

Thus, lungfishes combine in their organization, on the one hand, a number of very primitive characteristics such as the absence of vertebral bodies, a predominantly cartilaginous skeleton, and on the other hand, they have a real lung, the appearance of which is associated with the development of internal nostrils and a double circulation. Completely unique features include the biserial type of paired fins.

Skeleton

The spine is represented by a constant chord completely undivided into individual vertebrae. Segmentation is expressed here only by the presence of cartilaginous upper processes and cartilaginous ribs.

The skull (Fig.) has a wide base (platybasal type) and consists almost entirely of cartilage. Two small ossifications are noted in the occipital region; the skull is covered from above by several superficial bones; below there is one large bone corresponding to the parasphenoid of teleost fish (Fig. , 13). The palatoquadrate cartilage adheres to the skull (autostylous connection). The lateral parts of the skull on each side are covered by the temporal bones (squamosum = pteroticum; Fig. 2, 5). The operculum is represented by two bones. The gill splinters are absent from the cartilaginous gill arches. The shoulder girdle (Fig. 2) consists of thick cartilage, which is lined with a pair of integumentary bones. The skeleton of paired fins consists of a main axis, consisting of a number of cartilages, and cartilaginous rays, which support the fin blades on each side (Fig. 2, 13). This limb structure is called biserial. Gegenbaur believes that the simplest type of limb structure should be considered a skeletal axis bearing two rows of rays. This author calls such a limb an archipterygium and from it the limbs of terrestrial vertebrates are derived. The paired fins of the ceratod are built according to the type of archipterygium.

Rice. 2. Side view of a ceratod skeleton.

1, 2, 3-cover bones of the skull roof; 4-posterior cartilaginous part of the skull; 5 -pterotjcum (squamosum); 6-operculum; 7-suborbitale; 8-socket; 9 - shoulder girdle; 10-proximal pectoral fin cartilage; 11-pectoral fin; 12-pelvic girdle; 13-ventral fin; 14-axis skeleton; 15-tail fin.

I. I. Shmalgauzen (1915) admits that such an actively flexible fin of the ceratod with a reduced dermal skeleton developed as a result of slow movement and partly swimming in heavily overgrown fresh waters.

Digestive organs of lungfish

Of the characteristic features of the scaly plant, its teeth attract special attention. Each tooth is a plate, the convex edge of which faces inward; the tooth bears 6-7 sharp points directed forward. There are two pairs of such teeth: one on the roof of the oral cavity, the other on the lower jaw. There can hardly be any doubt that such complex teeth were the result of the fusion of individual simple conical teeth (Fig. 11).

A spiral valve stretches the entire length of the intestine, similar to the valve found in transverse-mouthed fish.

Breathing of lungfish

In addition to the gills, the neoceratod has a single lung, internally divided into a number of chambers with cellular walls. The lung is located on the dorsal side of the body, but communicates with the esophagus through a canal that opens on the abdominal part of the esophagus.

The lungs of neoceratodes (and other lungfishes) are close in both their position and structure to the swim bladder of higher fish. In many higher fish, the inner walls of the swim bladder are smooth, while in lungfishes they are cellular. However, numerous transitions are known for this feature. So, for example, the swim bladder of bony ganoids (Lepidosteus, Amia) has cellular internal walls. Apparently, we can definitely assume that the lungs of Dipnoi and the swim bladder of higher fish are homologous organs.

The pulmonary arteries approach the lung, and the pulmonary veins go from it; thus, it performs a respiratory function similar to that of varnish in terrestrial vertebrates.

Circulation

The characteristic features of its blood circulation are associated with the double breathing of the ceratode. In the structure of the heart, attention is drawn to the presence of a septum on the abdominal wall of the atrium, which does not completely separate the atrium cavity into the right and left halves. This septum protrudes into the venous sinus and divides its opening, directed into the atrium cavity, into two parts. There are no valves in the opening connecting the atrium to the ventricle, but the septum between the atrium hangs into the cavity of the ventricle and is partially attached to its walls. This entire complex structure determines the peculiarities of the function of the heart: when the atrium and ventricle contract, the incomplete septum is pressed against the walls and momentarily isolates the right halves of both the atrium and the ventricle. The peculiar structure of the arterial cone is also used to separate the blood flow from the right and left halves of the heart. It is spirally twisted and carries eight transverse valves, with the help of which a longitudinal septum is formed in the arterial cone. It separates the left abdominal duct of the cone, through which the arterial duct passes, from the right spinal duct, through which the venous duct flows.

Having become familiar with the structure of the heart, it is easy to understand the sequence in the mechanism of blood circulation. From the pulmonary vein, the arterial vein enters the left part of the atrium and ventricle, going to the abdominal section of the arterial cone. Four pairs of gill vessels originate from the cone (Fig. 3). The two anterior pairs start from the ventral side of the cone, and therefore receive pure arterial blood. The carotid arteries depart from these arches, supplying pure arterial blood to the head (Fig. 3, 10, 11). The two posterior pairs of branchial vessels are connected to the dorsal part of the cone and carry venous blood: the pulmonary artery branches off from the posterior pier and supplying venous blood for oxidation to the lungs.

Rice. 3. Scheme of the arterial arches of the ceratodes from the ventral side.

I, II, III, IV, V, VI-arterial arches; 7-gills; 8-efferent artery; 10- internal carotid artery; 11 - external carotid artery; 17-dorsal aorta; 19-pulmonary artery; 24-splanchnic artery.

To the right half of the heart (to the right section of the venous sinus, atrium,and then into the ventricle) all venous blood enters, which enters through the ducts of Cuvier and through the inferior vena cava (see below).

This venous blood is directed into the right dorsal venous duct, the conusaorta. Next, venous blood enters the gills, as well as the pulmonary artery. The body of the ceratode and its internal organs (except for the head) receiveblood oxidized in the gills; the head section, as mentioned above, receives blood that has received more vigorous oxidation in the lungs. DespiteSince the atrium and ventricle are completely divided into right and left halves, thanks to a number of devices described, isolation of pure arterial blood flow to the head is achieved (through the anterior pairs of vessels extending from the conus arteriosus and through the carotid arteries).

In addition to the sketch made, we point out that the venous system is characterized by the appearance of the inferior vena cava, which flows into the venous sinus. This vessel is absent in other fish. In addition, a special abdominal vein develops, also leading to the venous sinus. The abdominal vein is not found in other fish, but it is well developed in amphibians.

Nervous system

The central nervous system is characterized by strong development of the forebrain; the midbrain is relatively small, quite small.

Genitourinary organs

The kidneys represent the primary kidney (mesonephros); three pairs of renal tubules function only in the embryo. The ureters empty into the cloaca. Females have paired oviducts in the form of two long winding tubes, opening with their anterior cones (funnels) in the body cavity not far from the heart. The lower ends of the oviducts, or Müllerian canals, are connected at a special papilla, which opens with an unpaired opening into the cloaca.

The male has long, large testes. In neoceratodes, numerous seminiferous tubules lead through the primary kidney into the Wolffian duct, which opens into the cloaca. Note that males have well-developed oviducts (Müllerian ducts).

In other lungfishes there are some differences in the structure of the male genital organs compared to those described in Neoceratoda. Thus, in Lepido-siren, the seminiferous tubules (5-6 on each side) pass only through the posterior renal tubules into the common Wolffian duct. In Protopterus, one posterior tubule, which is present, has completely separated from the kidney and acquired the character of an independent excretory pathway.

Ecology. Cerathodus is quite common in marshy, slow-moving rivers. This is a sedentary, sluggish fish, easily caught by the person pursuing it. From time to time, the ceratod rises to the surface to take air into its lungs. The air is drawn in with a characteristic sound reminiscent of a groan. This sound is clearly audible on a quiet night, especially if you are on the water in a boat at that time. The pulmonary is an expedient adaptation during a period of drought, when a reservoir turns into a swamp: during this time many other fish die, and the lepidoptera seems to feel very well: at this time the pulmonary helps out the fish.

It should be noted that the predominant mode of respiration in the described species is gill; in this respect, it is closer to other fish than other representatives of lungfish. He lives in the water all year. When removed from its natural environment into the air, the ceratod quickly dies.

The food consists of small animal prey - crustaceans, worms, and mollusks.

Spawning from April to November. The eggs, surrounded by gelatinous membranes, are laid between aquatic plants.

The ceratod larva lacks external gills. Interestingly, the teeth do not merge into characteristic plates, but consist of individual sharp teeth.

Article on the topic Lungfish

Superorder Lungfishes (Dipnoi, or Dipneustomorpha) (V. M. Makushok)

Order Horntoothed (Ceratodiformes)

Horntoothed fish are the only branch of the once numerous lungfish that has survived to this day. Appearing in the Devonian period, lungfishes flourished until the Triassic, after which the group began to decline. To this day, of the two orders of lungfishes, numbering 11-12 families, only one order has survived: Horntoothed, with two families - Horntoothed(Ceratodidae) and squamate(Lepidosirenidae), with a total of 6 species. The areas of distribution of these relict forms - South America, tropical Africa and Australia - indicate the great antiquity of the group.

Modern lungfish are typically freshwater fish, perfectly adapted to life in water bodies that dry up during the dry season.

The most surprising thing for lungfish is the so-called “double” breathing, which is where their name comes from. They are able to carry this out due to the fact that in addition to the gills common to fish, they also have real lungs, which in essential features of their structure are similar to the lungs of higher vertebrates.

These lungs, which replace their swim bladder, are connected to the pharynx by a duct that enters it from the ventral side. In connection with the partial transition to pulmonary respiration, the postnostril openings of lungfishes open into the oral cavity, forming internal nostrils (choanae), which allows them to breathe atmospheric air with their mouth closed; Almost like amphibians, there is a pulmonary circulation, i.e. venous blood enters mainly into the lungs, which is also facilitated by the division of the atrium by an incomplete septum. Also closely related to pulmonary respiration is the presence of the inferior vena cava, which is characteristic of all terrestrial vertebrates, starting with amphibians, but is absent in all other fish except lungfishes.

The axial skeleton of lungfishes largely retains primitive features: there are no vertebral bodies, the cartilaginous bases of the upper and lower arches sit directly on the notochord, which is well preserved throughout life. The skull, along with ancient features, is characterized by a peculiar specialization. In the cartilaginous cranium (neurocranium), only one pair of replacement bones (lateral occipital) develops. There are a large number of peculiar integumentary bones of the skull. The palatoquadrate cartilage fuses with the base of the skull. On the vomer, pterygopalatine bones and lower jaws sit bony chewing dental plates, formed from the fusion of numerous small teeth and very similar to the plates of fused heads (4 plates on the upper jaw and 2 on the lower jaw).

The cartilaginous skeleton of the paired fins supports almost the entire fin blade, except for its outer edge, where it is supported by thin skin rays. This peculiar internal skeleton consists of a long articulated central axis, which in the horned teeth (Ceratodidae) carries two rows of lateral articulated cartilaginous elements, and in the squamate (family Lepidosirenidae) does not have these appendages or carries their rudiments. The internal skeleton of the fins is connected to the belt by only one main (basal) segment of the central axis and in this respect is to a certain extent similar to the limb of terrestrial vertebrates. The unpaired fins, dorsal and anal, are completely fused with the caudal fin. The latter is symmetrical and has a diphycercal structure (in many fossil lungfishes the tail was unequally lobed - heterocercal). The scales of ancient forms were of the “cosmoid” type; in modern lungfishes the upper enamel layer and dentin have been lost. The heart has a conus arteriosus; the intestine is equipped with a spiral valve - these are primitive signs. The genitourinary apparatus is similar to that of shark fish and amphibians: there is a common excretory opening (cloaca).

Despite the fact that, according to modern views, lungfishes represent a lateral branch of the main “trunk” of aquatic vertebrates, interest in this amazing group of animals does not wane, since in its example one can trace the evolutionary attempts of nature to make the transition of vertebrates from aquatic existence to terrestrial and from gill respiration to pulmonary respiration.

Family Horntoothed, or One-lunged (Ceratodidae)

This family includes several extinct genera, the fossil remains of which are found on all continents, and the modern genus Neoceratodifs, which is close to them, with one species. They are characterized by a cartilaginous neurocranium, the presence of one lung and well-developed flipper-shaped paired fins, which are supported by a segmented central axis and two rows of lateral segmented rays extending from it.

The only modern representative of the family horntooth, or barramunda(Neoceratodus forsteri) - found only in Queensland (North-East Australia), where it inhabits the Burnett and Mary river basins. IN Lately it was also transplanted into some lakes and reservoirs in Queensland, where it took root. Horntooth is a large fish, reaching a length of 175 cm and weights over 10 kg. Its massive body is laterally compressed and covered with very large scales, and its fleshy paired fins are somewhat reminiscent of penguin flippers. Colored in uniform tones - from reddish-brown to bluish-gray, which are somewhat lighter on the sides; the belly is usually whitish-silver to light yellow.

The horntooth lives in rivers with a slow current and heavily overgrown with aquatic vegetation. Like all fish, it breathes through gills, but in addition, every 40-50 minutes it rises to the surface to breathe atmospheric air. Extending the tip of its snout above the water, the horntooth forcefully throws out the spent air from its only lung, while emitting a characteristic groaning-grunting sound that carries far throughout the surrounding area. Immediately after this, taking a deep breath, he slowly sinks to the bottom. He exhales and inhales through his nostrils with his jaws tightly closed. It must be admitted that when breathing atmospheric air, the actions of the horntooth resemble the actions of cetaceans. Even when in water containing a sufficient amount of oxygen, the cattail, apparently, cannot be content with gill respiration and supplements it with pulmonary respiration. The latter is especially useful for it in dry seasons, when river beds dry up completely over large areas and when water is stored only in the deepest pits (barrels). In such gradually drying shelters, many fish, including cattails, accumulate in search of salvation. When almost all oxygen disappears in overheated stagnant water as a result of putrefactive processes and all other fish die from suffocation, the cattail continues to thrive, switching to breathing atmospheric air. And even when, during a prolonged drought, these shelters turn into a cemetery for all living things, and the water in them turns into a fetid slurry in which hundreds of corpses of dead animals decompose - even then the cattail survives, waiting for the saving rains. However, complete drying out of the reservoir is also disastrous for it, since it cannot hibernate by burying itself in the ground, like its African and South American relatives. A cattail pulled out of the water is completely helpless and dies sooner than many other fish, losing its lungs.

The horntooth is a sluggish and sedentary animal. It usually spends most of its time at the bottom of deep pools, where it lies on its belly or stands, resting on its paired fins and the tail of its body. In search of food, it slowly crawls on its belly, and sometimes walks, relying on the same paired fins. In the water column, it, as a rule, moves slowly due to barely noticeable bending of its body. Only if it is startled does the horntooth use its powerful tail and demonstrate its ability to move quickly. Apparently, the circadian rhythm of this animal is weakly expressed and the cattail often shows its sluggish activity at any time of the day or night. Its food consists of various invertebrates (molluscs, crustaceans, insect larvae, worms, etc.). True, the intestines of the cattail are usually filled with finely chewed plant remains, but, apparently, plant food is not digested by it, but is captured along with invertebrate animals. At least in captivity, he is content with “modest” food without any harm, showing no need for a “vegetarian” diet.

Spawning of the cattail is very extended and lasts from April to November. It is most intense in September-October, when the rainy season begins, the rivers swell and the water in them is well aerated. The horntooth lays eggs on aquatic vegetation and does not show further care for the offspring. Since the shell of the eggs is not sticky, many of them roll off and fall to the bottom; It is not entirely clear how this affects their survival. The eggs are quite large, they reach a diameter of 6.5-7.0 mm and are enclosed in a gelatinous shell, which makes them very similar to frog eggs. This similarity is aggravated by the large amount of yolk and the peculiarities of embryonic development.

The development of eggs lasts 10-12 days. Unlike the larvae of lepidopterans and protopterans, the larvae of the horntooth completely lack external gills and a cement organ. Before their yolk sac dissolves, they lie motionless on their side at the bottom and only from time to time, as if roused, jump to another place nearby in order to freeze again in the same position. With the transition to active feeding, the larvae stay in quiet and shallow pools, where they initially feed on filamentous algae, eventually switching to feeding on invertebrates. Their pectoral fins, as a rule, appear on the 14th day after hatching, and the ventral fins appear much later (about two and a half months).

The horntooth is consumed as food, and its reddish meat is highly prized by both aborigines and white settlers. The horntooth can be easily caught on a hook at any time of the day, but there are periods lasting up to a week or more when it does not take any bait. The natives are very skilled at catching (or rather, catching) the horntooth, using small homemade nets for this purpose. Taking such a net in each hand, the fisherman dives into a deep hole, trying to find the fish lying at the bottom. Carefully bringing the nets simultaneously to the head and tail of the cattail, the fisherman grabs the fish with them and floats to the surface with it. It is unlikely that any other fish shows such inertia as to allow itself to be captured with bare hands.

Even a touch does not always scare away the horntooth. And if he is still disturbed, then, still not feeling the danger, he uses his strong tail and with a sharp jerk leaves the annoying fisherman to again lie motionless nearby. In this case, it costs nothing to resume the pursuit. Apparently, such a disregard for danger was developed by the horntooth at a time and in those conditions when he had no enemies and had no one to fear. Only when caught in a snare or on a hook does the phlegmatic horntooth show remarkable strength and fiercely fight for its life. But he is not capable of a long fight: his fury is quickly exhausted, and he limply surrenders to the will of the winner.

In captivity, this peaceful animal gets along well with other fish and its own kind.

One of the most amazing hoaxes known to zoology is associated with the horntooth. Its beginning dates back to August 1872. At this time, the director of the Brisbane Museum was touring northern Queensland. One day he was informed that a breakfast had been prepared in his honor and that for his sake the natives were not too lazy to deliver to the table a very rare fish that they had caught 8-10 miles from the place where the feast was to take place. The flattered director accepted this offer and indeed saw a fish of a very strange appearance: its long, massive body was covered with powerful scales, its fins resembled flippers, and its snout resembled a duck’s beak. Before paying tribute to such an unusual dish (needless to say, the fish was already cooked), the director made a sketch of it, and, returning to Brisbane, handed it over to F. de Castelnau, then the leading Australian ichthyologist. Castelnau was not slow in using this drawing to describe the new genus and species Ompax spatuloides, which he classified as a lungfish. This publication sparked quite a heated debate about the relationship of Ompax and its place in the classification system. There were many reasons for controversy, since in the description of Ompax much remained unclear and there was no information on anatomy at all. Attempts to obtain a new specimen were unsuccessful. As always, there were skeptics who expressed doubt about the existence of this animal. Nevertheless, the mysterious Ompax spatuloides continued to be mentioned in all reference books and reports on the Australian fauna for almost 60 years. The mystery was resolved unexpectedly. In 1930, a note appeared in the Sydney Bulletin, the author of which wished to remain anonymous. This note reported that an innocent joke was played on the simple-minded director of the Brisbane Museum, since the “Ompax” served to him was prepared from the tail of an eel, the body of a mullet, the head and pectoral fins of a horntooth and the snout of a platypus. From above, this entire ingenious gastronomic structure was skillfully covered with scales of the same horned tooth.

So Ompax spatuloides was deleted from the faunal lists, and the cattail remained the only living representative of lungfish in Australia.

Family Lepidosirenidae

Lepidoptera are characterized by an elongated eel-like body, which right up to the ventral fins is rounded in cross section. They have a paired lung, small cycloid scales covering their body and part of the head are deeply hidden under the skin, and their flexible paired fins have a rope-like shape. Most characteristic of fish of this family is the ability to exist throughout their lives in temporary bodies of water, which often dry up completely during the dry season, which sometimes lasts up to 9 months. During this entire time, they hibernate, burying themselves in the ground and completely switching to breathing atmospheric air. There are 5 species in this family: 4 species living in tropical Africa belong to the genus Protopterus, and the South American genus Lepidosiren is represented by only one species.

The affinity between South American and African representatives freshwater lungfish is a strong argument in favor of the existence of land connections between Africa and South America in the distant past.

Perhaps the most significant difference between protopterans and squamates is that the former have 6 gill arches and 5 gill slits, while the latter have only 5 gill arches and 4 gill slits. Sometimes they are considered as representatives of special families (Lepidosirenidae and Protopteridae).

Four species of the genus Protopters(Protopterus) are very similar in appearance and differ from each other in their coloring, number of ribs, degree of development and width of the skin edge of paired fins and other characteristics.

Most close-up view - large protopter(Protopterus aethiopicus, local name"mamba") - sometimes reaches a length of over 2 m, painted in bluish-gray tones, with numerous small dark spots, sometimes forming a “marble” pattern. This species lives from Eastern Sudan to Lake Tanganyika.

Small protopter(P. amphibius), apparently the smallest species, not exceeding 30 in length cm. It lives in the Zambezi Delta and in rivers southeast of Lake Rudolf. Its juveniles are characterized by the presence of three pairs of external gills, which persist for a very long time.

Dark Protopter(P.dolloi), found only in the Congo Basin, is characterized by the most elongated body and very dark coloration. Reaches a length of 85 cm. Externally, this species is most similar to the South American lepidoptera.

Brown Protopter(P. annectens), reaching 90 cm length, is a common lungfish of West Africa. It inhabits the river basins of Senegal, Gambia, Niger and Zambezi, Lake Chad and the Katanga region. The back of this species is usually brown-green, the sides are lighter, and the belly is off-white. The biology of this species is the most well studied.

The climate of tropical Africa is characterized by abrupt change rainy and dry seasons. The rainy season begins in May-July and lasts 2-3 months, while the rest of the year is dry. During periods of stormy tropical downpours, rivers swell and overflow, flooding vast areas of lowlands in which water remains for 3-5 months of the year. Masses of fish rush from the rivers into these temporary reservoirs, where there is an abundance of easily accessible food, but as they dry out, escaping death, the fish return to the rivers before the channels become shallow. The protopter behaves completely differently. It turns out that, as a rule, it does not live in rivers at all, but constantly lives in such temporary reservoirs and its entire life rhythm is closely connected with their hydrological features.

Local fishermen of the Gambia River basin, who know the habits of the protoptera well, say: “Kambona (as they call the protoptera) is an extraordinary fish: it does not leave after the water, but the water itself comes to it.”

During rainy times, the protopter leads an active lifestyle in these reservoirs - it feeds, reproduces and grows. And during the dry period, it hibernates, spending it in specially constructed nests.

With the onset of the dry season and as temporary reservoirs dry up, protopters begin to prepare for hibernation: large fish do this when the water level drops to 10 cm, and smaller ones - when the water layer does not exceed 3-5 With m. Usually in such reservoirs the bottom is covered with soft silt, which contains a large amount of plant debris. Under a layer of silt reaching a thickness of 2.5-5 cm, there is dense clay mixed with fine sand.

The protopter digs its “sleeping nest” with its mouth. Having sucked another portion of silt into the oral cavity, it forcefully throws it out along with the water through the gill openings. Soft silt is easy to "drill", but the underlying layer of dense clay is much more difficult to dig. Making energetic swimming movements with its whole body, the fish rests its snout on the ground and gnaws out a piece of clay. The bitten off piece is chewed, thrown out with water through the same gill openings and removed from the hole in the form of a cloud of turbidity with ascending currents of water created by bending the body. Thanks to this, larger particles of crushed clay settle in the immediate vicinity of the inlet, which is essential for creating a safety cap that completes the construction.

Having reached the required depth, the fish expands the lower part of the hole (the “bedroom”) just enough to be able, folded in half, to turn over in it with its head up. Now the “sleeping nest” is almost ready, and the animal waits for the water to completely subside, sticking its snout out of the inlet and from time to time rising to the surface to breathe atmospheric air. When the film of drying water reaches the upper edge of the liquid silt lining the bottom of the reservoir, then, thanks to the respiratory movements produced by the fish, part of the clay thrown out at the inlet is sucked into it and clogs the outlet. After this, the animal no longer comes to the surface. Before this “plug” dries completely, the protopter, poking its snout into it, compacts it from below and lifts it somewhat in the form of a cap, which often has cracks.

The cap camouflages the sleeping nest and prevents it from becoming clogged, while being strong enough to withstand destruction. At the same time, the admixture of small grains of sand makes it porous enough to allow air to pass through, which is further facilitated by cracks. As soon as the cap hardens, the water in the burrow becomes viscous due to the abundance of mucus secreted by the protopter. As the soil dries, the water level in the entrance chamber gradually drops, as a result of which it turns into an air chamber, and the fish, obediently following the surface of the water, sinks lower and lower into the expanded lower part of the hole, i.e. into the “bedroom” where, finally, she freezes in her characteristic position.

A visiting naturalist experiences an amazing feeling when, accompanied by local residents For the first time he goes in search of the protopter's "sleeping nests". It’s hard to believe that the plain, cracked by the heat, covered with scorched vegetation, was recently the bottom of a reservoir and that somewhere nearby, hundreds and thousands of fish sleep in the petrified earth. He is greatly surprised when the natives, almost crawling on their knees, begin to carefully examine the soil inch by inch. It soon becomes clear that they are looking for small elevations with a diameter of 5-15 cm, which differ from the surrounding soil, painted in more or less gray tones, by a brownish tint. One blow with a hoe is enough to reveal a hole going deeper under such a cut tubercle. In other words, each such mound represents a so-called safety cover, or cap, which covers the entrance to the protopter’s “sleeping nest” from above. With an experienced eye, these mounds can be detected without difficulty. Only in small fish, less than 15 cm, they are so weakly expressed that they are almost impossible to find.

The circular passage, usually running vertically downwards, has smooth walls. This is the so-called air chamber. Its diameter ranges from 5 to 70 mm, and length - from 30 to 250 mm. These dimensions depend only on the size of the hibernating fish. Even the length of the air chamber does not depend on whether the “nest” was built in a deep or shallow place. Below, the air chamber gradually expands and passes into the so-called “bedroom”, where the fish enclosed in a cocoon rests. In large fish, the “bedroom” lies at a depth of up to half a meter.

A sleeping protopter, as a rule, takes a strictly defined position. Its snout is always directed upward, and its body is folded in half so that the bend is in the middle between the pectoral and ventral fins, in other words, these fins are side by side and at the same level. The folded front and rear parts of the body are pressed very closely together, and the flattened tail overlaps the top of the head and is pressed just as tightly to the back. In this case, the lower edge of the tail, which completely covers the eyes, runs along the edge of the upper jaw, leaving the slightly open mouth free. The fish curled up in this way is enclosed in a kind of cocoon. In the world of fish, only representatives of the genus Protopterus can create this unique formation.

The cocoon is a thin film with a thickness of 0.05-0.06 mm, formed when the mucus hardens, which is secreted by fish preparing for hibernation. Its walls consist of mucin with a small admixture of inorganic compounds (they are based on calcium carbonate and calcium phosphate), transferred from the soil at the time of formation of the cocoon. The cocoon is a solid formation (without any constrictions) and fits the sleeping protopter so tightly that there are no gaps left between its walls and the body of the fish. The wrinkled paired fins of a sleeping fish are pressed very tightly into the body and do not leave any marks on the inner wall of the cocoon. The rounded upper part of the cocoon, which follows the contour of the walls of the air chamber at the point where it transitions into the “bedroom,” is flattened and slightly hilly directly above the fish’s mouth. This rise has a small depression at the top, in the center of which there is an opening of a funnel-shaped tube 1-5 long mm, leading straight into the slightly open mouth of the sleeping protopter. It is through this tiny breathing hole that the only connection between the fish and the external environment occurs. Usually the cocoon is colored to match the color of the reddish-brown soil due to the coloring inorganic substances contained in the soil. In cases where these substances are absent, the cocoon can be transparent, like cellophane. Its inner wall is always wet, since the body of the fish remains covered with mucus until the end of hibernation.

The ability of the protopter to “put on” a cocoon during hibernation is so unusual and amazing that the first researchers who saw this cocoon could not believe their own eyes. Contrary to obvious evidence, they mistook the walls of the cocoon for dried leaves, suggesting that the fish going to sleep wrapped itself in them, sticking them to itself with thick mucus. So, wrapped in fantastic leaves, like in some kind of swaddling clothes, the sleeping protopter was depicted in Jerdain’s publication, which appeared in 1841. And this was not a joke.

It is quite natural that in order to maintain its vital functions, a protopter sleeping in a cocoon must not only breathe, consuming oxygen, but also eat, i.e., consume some reserves of “fuel”, and do something with decay products, an excess of which in the body usually leads to fatal outcome.

In contrast to all other vertebrate animals that hibernate, the protoptera, enclosed in a cocoon, does not consume fat reserves, but its own muscle tissue. At the beginning of hibernation, his metabolism still occurs at a fairly high energy level, but gradually it freezes and proceeds further in a very economical mode, since, otherwise, it would not have enough “fuel,” i.e., muscle tissue. During hibernation, the protopter loses a lot of weight. So, for example, a fish 40 long cm, weighing 374 g, after a six-month stay in the cocoon had a length of 36 cm and weighed 289 g, i.e., she lost more than 20% in weight and decreased in size by 10%. Such relatively large losses are explained by the fact that during hibernation, protoptera tissues are spent not only on maintaining the vital functions of the body, but also on the maturation of the gonads. Losses are replenished quite quickly: the same fish regained its weight within a month and reached its previous size.

During protopter hibernation, all the water formed during the breakdown of proteins is lost during respiration and urine is not excreted (and there would be nowhere to remove it, since the fish is enclosed in a cocoon that tightly fits its body). Therefore, the resulting urea accumulates in the body in huge quantities, amounting to 1-2% of body weight by the end of hibernation, which should be considered as an amazing physiological paradox: for most vertebrates, excess urea in the body acts as a strong poison, and death occurs when its concentration is 2 thousand times less than that of a sleeping protopter, to which it does not cause any harm. Within a few hours after the protopter enters the water, all excess urea is eliminated from the body through the gills and kidneys.

Depending on local conditions, which vary significantly from year to year, the protopter spends 6-9 months in hibernation. An interesting record was broken by the brown protoptera, which, under experimental conditions, spent more than four years in continuous hibernation without any harmful consequences for itself. However, in cases where reservoirs do not dry out, protopters do not hibernate. This is easy to achieve in aquarium conditions. Nevertheless, it was noticed that protoptera, “awake” for a number of years, kept in an aquarium (one of them spent 13 years without hibernation), from time to time become lethargic, inactive and even refuse food. This condition is noticed in them on average once a year and lasts from several weeks to two to three months without any signs of the disease.

It is almost certain that this behavior is associated with the innate habit of hibernation and that hibernation is an integral part of the life rhythm of these fish. For the sake of accuracy, it should be added that these observations were made on individuals of the brown protoptera caught in the river basin. Gambia, where this species usually hibernates. It is possible that in protopters of other species this rhythm is not so pronounced. It is known, for example, that in the Great Lakes Central Africa Protopters do not enter into annual hibernation, since they do not have the need or appropriate conditions for this.

With the onset of the rainy season, dry reservoirs quickly fill with water, and the protopters return to active life from their voluntary confinement. The very process of their awakening in nature has not yet been traced, but it can be judged by a special experiment carried out in 1931. This simple experiment consisted in the fact that pieces of clay cut out of the ground with protopters enclosed in them were buried in a shallow puddle so that the layer of water above them did not exceed 5 cm. About an hour later the first fish appeared at the outlet. After a short reconnaissance, she rose to the surface of the water and greedily swallowed air, only to immediately hide in the nest. At first, these actions were repeated every 3-5 minutes, but gradually the intervals between successive exits to the surface lengthened to the usual 10-20 minutes. At the same time, the fish hid less and less in the nest, until after 6-7 hours it left it completely.

It has been noticed that the longer the protoptera's hibernation lasts, the more time it takes for it to shake off sleep. During the first few days, fish that have spent 7-8 months in hibernation have little control over their movements, moving in sharp and clumsy jerks, like cripples. At the same time, their tail remains bent upward and somewhat to the side for quite a long time, and the crumpled paired fins only gradually straighten and acquire elasticity.

Protoptera is an omnivorous fish. The basis of its food is a variety of shellfish, crabs, shrimp and partly fish. Having captured the prey, he does not swallow it, but throws it out of his mouth, holding it by the very tip, and begins to chew methodically until it is all hidden in his mouth. Then he spits it out again and chews it again. And so on several times. It does not grab the prey, but sucks it in, and does this with incomprehensible speed and agility. It is possible that it is precisely at this time that individual parts of plants are captured, the remains of which are often found in his stomach.

To those who have observed protoptera in an aquarium, these fish give the impression of sluggish and sedentary animals. But this impression is deceptive, since protopters lead night look life and go hunting after dark. At this time, their activity increases sharply, and they often rise to the surface to breathe atmospheric air. Protopters move in two ways: they either swim due to the eel-like bending of the body, or they move along the bottom and among bottom vegetation with the help of paired fins, and, in addition to motor functions, these fins play an important role in finding prey, since they are densely dotted with taste buds (the pectoral fins are especially abundantly covered with them). It is worth imagining a protoptera hunting at night among dense thickets of aquatic vegetation in muddy water to understand what a minor role vision can play in these conditions. This is where the long and flexible paired fins come to the rescue, with which the crawling fish explores the space around it to “taste”. As soon as the protopter touches an edible object with one of its four fins, with a lightning-fast throw it jumps up to the prey and sends it into its mouth.

The development of gonads in the protoptera begins immediately after spawning, and most of the time for their maturation occurs during the period of hibernation. Already in August-September, i.e. a month and a half after the start of the rainy season and the end of hibernation, spawning begins, which lasts about a month. By this time, a special brood nest is being built. It is usually built in shallow water, where the water layer does not exceed 40-50 cm and where the bottom is overgrown with thick grass, often reaching a height of two meters. Typically, such a nest is a horseshoe-shaped hole with two entrance holes. One of them - wider - has a diameter of 20-30 cm, and the other, narrower one, is only 10-15 cm. In the lower part of this hole, lying at about a depth of 40 cm from the ground surface and farthest from the entrance holes, there is an expanded brood chamber in which eggs are laid and larvae are kept. Sometimes nests have three entrance holes leading to a common brood chamber, or only one exit when steep hummocks or artificial earthen embankments are used to build the nest, dividing rice fields. The walls of the nest are not covered with mucus and are not specially strengthened with anything: it is protected from collapse by dense soil, held together by numerous plant roots. There is no bedding in the brood chamber, and eggs are laid directly on its clay bottom. Since nests are built in shallow water, in order to get to deeper water, protoptera make peculiar “paths”, crushing and pushing apart thick grass. Usually, brood nests are found along these “paths,” since in muddy water among lush vegetation it is very difficult to detect the entrance hole in any other way, unless you accidentally fall into it. Often the “paths” stretch for several meters, and when the water level drops sharply (which happens quite often), the protopters have to get to the water by land. But even with very sharp fluctuations in water level, the nests themselves never dry out. In some places, such nests are located in close proximity to each other at a distance of 7-8 m.

The male takes all care of protecting the nest and offspring. He selflessly defends his nest and viciously bites anyone who dares to approach him, without retreating from humans (the natives are afraid of his violent attacks). Even if you drive him out of the nest with a stick, he fearlessly returns after a few minutes. Hiding in one of the holes, the male supports D.C. water in the brood chamber due to undulating movements of the tail. He stops caring for the offspring only when the larvae leave the nest.

No one has been able to observe the process of building a nest, and it is still unknown whether the male or female builds it, or whether they build it together. Judging by the fact that the female does not take any part in protecting the nest and offspring, it is preferable to think that the male builds the nest. Protopter eggs have a diameter of 3.5-4.0 mm. Their number in one clutch reaches 5 thousand, but there are often cases when there are significantly fewer of them. Moreover, very often in the same clutch there are two (or even three) portions of eggs that differ sharply in the degree of their development (for example, one portion of eggs may be at the stage of beginning crushing, while another portion is at the stage of beginning gastrulation). In the same way, among the larvae of the same litter, in some cases it is easy to distinguish two (and sometimes three) mixed age groups, differing in body length by 7-8 mm. Usually in such cases, the differences in the degree of development are 1-3 days, and sometimes more. Apparently, either several females sequentially lay their eggs in the same brood chamber, or the same female lays them in portions at fairly significant intervals of time.

The hatched larvae attach themselves to the walls of the brood chamber with the help of a cement gland, where they hang almost motionless until their yolk sac dissolves. The presence of four pairs of external gills allows them to do without air breathing. The larvae grow very quickly and within three weeks reach a length of 20-25 mm. By this time, they have lost their yolk sac and begin active feeding, rising to the surface of the water to breathe atmospheric air.

Upon reaching 30-35 mm length, a little more than a month after hatching, the larvae leave the nest forever. By this time, they have lost one pair of external gills. The remaining external gills are reduced very late, and even for several years, adult fish retain rudiments of their basal parts. Before the onset of the dry period, the larvae manage to reach a length of 70-120 mm, and they acquire the ability to burrow into the ground for hibernation and form a cocoon already at a body length of 40-50 mm.

In captivity, protopters are very undemanding and unpretentious, so much so that they can live in the most rotten and muddy water. Interestingly, however, at the New York Aquarium they were unable to live in dechlorinated tap water. Only after this water was distilled did they feel tolerable.

Protopters are easy to train if handled appropriately. So, for example, if feeding is preceded by knocking on the wall of the aquarium, then after 2-3 weeks, having heard the signal, the fish show excitement and go to the place where food awaits them. As opposed to peaceful American scalefish(Lepidosiren paradoxa) all types of protoptera are distinguished by their ferocious and quarrelsome disposition. Placed together, they know no mercy and fight until the lucky winner remains alive. If you add any other large fish to the protopter, which it obviously cannot use as food, then it nevertheless pursues them and maims them. Only young protopters, when there is no other choice, can be kept together. But sooner or later they attack each other so violently that they soon find themselves without fins. Fortunately, bitten off fins are restored very quickly.

Typically, protoptera are delivered to aquariums in Europe and America in a cocoon. This method of transportation is extremely convenient, but requires great care, since due to shaking, the cocoon can easily tear, which leads to the inevitable death of the fish. It is also remarkable that in cases where the cocoon of a hibernating fish comes into contact not with the ground, but with some foreign body (for example, with the glass wall of an aquarium), this inevitably leads to death. That is why, in artificial conditions, the lower part of the aquarium wall must be coated with a thick layer of clay.

If you disturb the protoptera in its “sleeping nest”, it makes sounds that are reminiscent of both squeaking and creaking, which, apparently, is associated with “gnashing of teeth” in the literal sense of the word. An irritated fish out of water can make sounds similar to a loud scream. The same sound is heard when air is forcefully expelled from the lungs of a caught fish. IN natural conditions When breathing atmospheric air, the protopter emits a loud sigh, often turning into a kind of screech, heard at a long distance.

In many areas of Africa local population hunts for protopters, as their meat is excellent taste qualities. These fish are most easily caught during hibernation. Naturally, for this you need to know the places where they hibernate. It turns out that residents of the Gambia can detect these places by ear, since, according to them, in calm weather, at a considerable distance, you can hear the breathing of a large “kambona” (P. annectens) buried in the ground. None of the researchers were lucky in this regard.

According to many researchers, the original method of catching protopters is used by the inhabitants of Sudan. They use a special drum that produces sounds that simulate falling raindrops. Having succumbed to deception, the protopters wake up and make a loud smacking sound, thereby giving away their hiding place, and sometimes even crawl out of their nests, falling straight into the hands of the catchers.

American scalefish, or lepidosiren(Lepidosiren paradoxa) inhabits central part South America. Its range covers almost the entire Amazon basin and the northern tributaries of the Paraná.

But the structure and lifestyle of lepidosirens is very similar to its African relatives. Compared to protopterans, its body is even more elongated and even more reminiscent of the body of an eel, the paired fins are even more underdeveloped (the lateral cartilaginous supporting elements in them completely disappear) and shortened, the scales are hidden even deeper into the skin and are even smaller. This large fish, reaching a length of 125 cm, colored grayish-brown with large black spots on the back.

The lifestyle of lepidosiren in its main features is also very similar to the lifestyle of protopters. As a rule, it inhabits only temporary swampy bodies of water, heavily overgrown with aquatic vegetation. It is especially numerous in such reservoirs, which are found in abundance on the plains of the Gran Chaco. These reservoirs fill with water during the tropical rainstorms (April to September) and tend to dry out during the dry period that occurs during the rest of the year.

As the reservoir dries out and as the amount of oxygen in the water decreases, lepidosirens increasingly resort to breathing atmospheric air. When the layer of water becomes very small, it digs itself a “sleeping nest” and goes into hibernation, switching completely to breathing atmospheric air. In its shape, the “sleeping nest” of the lepidosiren is no different from the “sleeping nest” of the protopter and, like the latter, consists of an expanded “bedroom” and an air (or entrance) chamber, covered on top with a safety cap. In addition to the top cap, the lepidosiren sometimes has an additional plug of soil in the air chamber. Occasionally there are nests even with two additional plugs.

Lepidosirenus, lying down in the “bedroom,” takes exactly the same position as the protopterus, but unlike the latter, it is apparently not capable of forming a cocoon. True, it has never been possible to detect its nest in dry soil: at least at the “bedroom” level, the soil always remains moist, and, as a rule, it retains water mixed with mucus secreted by a sleeping animal.

In years with abundant rainfall, temporary reservoirs sometimes do not dry out even during periods of drought and lepidosirens do not hibernate.

With the beginning of the rainy season, when dry reservoirs are filled with water, lepidosiren leaves its “sleeping nest” (and it does this as carefully and prudently as the protopter) and pounces on food, showing extraordinary gluttony. It feeds on various invertebrate animals and mainly on large snails, ampullaria. Apparently, plant foods play a significant role in its diet, especially in juveniles. Lepidosiren spends almost all of its time at the bottom, where it either lies motionless or slowly crawls on its belly among dense thickets of vegetation. From time to time it rises to the surface to breathe atmospheric air. First, he sticks his snout out of the water and exhales. Then on a short time disappears under the water and, exposing its snout again, takes a deep breath. After this, the animal slowly sinks to the bottom, releasing excess air through the gill openings.

Not even two or three weeks pass after the end of hibernation before lepidosiren begins to reproduce. Just like the protopter, by this time he digs a brood nest, which is a rather deep hole 15-20 wide cm with one outlet, usually going vertically down and having a horizontal elbow that ends in an extension. Typically, such burrows reach a length of 60-80 cm, but there are often cases when they are 1-1.5 in length m. Eggs with a diameter of 6.5-7.0 mm are deposited on dead leaves and grass, which are specially dragged into the brood chamber. The male takes over the protection of the nest and offspring. During the spawning period, numerous branching outgrowths 5-8 in length develop on its ventral fins. cm, penetrated by numerous blood vessels. The functional purpose of these formations is not yet entirely clear. According to one version, oxygen is released from the blood through them and more favorable conditions are created for the development of eggs and larvae. According to another version, on the contrary, these outgrowths play the role of additional gills, since the male guarding the nest does not come to the surface and is deprived of the opportunity to breathe atmospheric air. After the male leaves the nest, these outgrowths on the pelvic fins are reduced and remain in the form of small tubercles. The mucus covering the body of the flake has coagulating properties and is capable of clearing turbidity from water. This has a beneficial effect on the development of eggs and larvae.

Lepidosiren larvae, like protopteran larvae, have external gills and a cement gland with which they are suspended in the nest. The larvae grow quite quickly: two months after hatching, i.e., by the time the yolk sac is absorbed and the transition to active feeding, they reach a length of 55 mm. However, the larvae begin to breathe atmospheric air long before this (at a length of 32-40 mm), when they are still in the nest under the protection of the male. Their external gills disappear soon after they leave the nest.

After spawning, lepidosiren continues to eat intensively, replenishing losses incurred during hibernation and spawning, and creating fat reserves for the duration of the upcoming hibernation. Unlike protopters, during hibernation it consumes fat, which is deposited for future use in large quantities in the intermuscular tissues.

There is evidence that this fish is capable of making sounds reminiscent of a cat's meow.

The Indians hunt lepidosiren for its tasty meat.

In captivity, lepidosiren is very unpretentious, peaceful and easily gets along with other fish.