Legless amphibians. Legless amphibians: representatives
I came across a rather interesting book called "Reproductive Biology and Phylogeny of Gymnophiona (Caecilians)". Something like a monographic description of this amazing order, which belongs to amphibians. Although they don’t look anything like amphibians (in the broad sense of the word). In general, I decided to make a short post about them. Moreover, there is almost no information on the intranet.
Legless amphibians are the smallest (165 species, grouped into 32 genera and 5 families) and the most primitive group of modern amphibians. Like fish, legless amphibians retained biconcave (amphicoelous) vertebrae with well-developed notochord remnants between them. Among other primitive signs, experts note an incomplete septum between the atria, the articulation of the auditory ossicle with the quadrate bone, short lower ribs and some others. Their occupation of one of the lowest steps on the “evolutionary ladder” of amphibians is also indicated by the presence in the skin of many representatives of bone scales, “inherited” from their extinct ancestors - stegocephalians, whose body was covered with skin ossifications.
Bone scales of legless amphibians are specific formations secreted by two types of skin glands, which can be located both in epithelial connective tissue (mainly in Caecilia spp.), and in overgrown skin grooves. They form ring or semi-ring transverse rows, usually consisting of several (up to eight) scales. Their number in the body can reach 2000, and in the front part the scales are smaller (up to 1 - 2 mm) than in the back (about 4 mm). In the most mobile areas of the body (in the tail area, for example), they are destroyed, leaving small cavities in the thickness of the skin.
The most characteristic feature of legless amphibians is the worm-like (snake-like) shape of the body without a tail (which is expressed only in the most primitive forms), limbs and even their belts, and the body is divided by constrictions into segments.
The annular segments are bounded by grooves, the edges of which are in contact with each other and form cavities that stick together and become overgrown in some species. In some cases, one segment is located above one vertebra, however, in many species the number of rings does not correspond to the number of vertebrae, since the wide occipital rings (called the collar) account for 3-4 vertebrae, and the caudal segment, clearly visible when located only in front of the anal hole, - 2 - 5.
In species of the genera Epicrionops and Ichthyophis, the number of grooves is less than the number of vertebrae. Representatives of the genus Ichthyophis have segments that are not strictly vertical, but somewhat oblique, arching like a wedge on the upper side of the body.
It is no coincidence that since the first mention of legless amphibians in 1735 by the famous zoologist and collector Albert Seba, for such a segmented body, similar to annelids, they are called caecilians. Many famous researchers of the past (Linnaeus, Laurenti, Latreille, Daudin, Rey) classified caecilians as snakes. Only in 1807 did Dumeril point out their relationship with frogs and toads, and Oppel in 1811 legitimized this view by giving them the name Apoda. Some researchers in the past considered caecilians to be degenerate salamanders.
The relatively monotonous lifestyle of legless amphibians affected the low degree of variability in body shape. Variability is mainly manifested in the thickness of the body. There are species (leatherback caecilian - Dermophis mexicanus(Dumeril et Bibron, 1941), for example), in which it changes throughout the entire length of the body. In others (Bombay fish snake - Ichthyophis bombayensis Taylor, 1960, in particular) the head and body have the same diameter, decreasing towards the rear. However, a number of species are characterized by a narrow-headed body that widens towards the tail. The most long view considered to be a gigantic caecilian ( Caecilia thompsoni Boulenger, 1902) - 1375 mm, and possibly up to 1.5 m, the width of its body is 92 times its length. At the same time, the shorter true and black caecilians ( Caecilia tenticulata Linnaeus, 1758; S. nigricans Boulenger, 1902) due to their great thickness, sometimes look much more massive and larger. The smallest legless amphibians are considered to be tiny and short caecilians - Idiocranium russelli Parker, 1936; Grandisonia brevis(Boulenger, 1911). Their maximum sizes are 114 mm (the length exceeds the width on average by 25 times) and 112 mm (14 times), respectively, although many individuals are able to reproduce already with a body length of 5 cm.
Caecilians lead a predominantly burrowing lifestyle, making passages in moist soil (although there are also aquatic forms), which left its mark not only on their appearance (absence of limbs and elongated body), but also on their shape internal organs: the left lung has lengthened, and the right has shortened (as in snakes). Their kidneys have become narrow and ribbon-like, the number of vertebrae in a number of species reaches 200 - 300. Their eyes are hidden under the skin or even under the bones (in Scolecomorphus spp.). In a number of caecilians, however, there are usually transparent “windows” above the eyes, and the retina contains only reduced optic rods without cones.
Due to the loss of vision, their sense of smell and touch developed greatly. These functions in legless amphibians are performed by special paired tentacles 2 - 3 mm long, visible only in adult specimens and located in special skin pits. In addition, it is believed that the tentacle is able to sense the moisture, consistency and temperature of the substrate (soil). In this case, the caecilians feel underground objects first from the left side, and then from the right. The duct of the large ocular (also called Harderian) gland opens into the tentacle fossa, the secretion of which in other vertebrates provides lubrication of the eye, although it was previously assumed to be poisonous. The tentacle of representatives of the family Scolecomorphidae is capable of pushing the eye through the opening of the tentacles in the skull from under the skull, placing it in this way above the skull.
The underground lifestyle also affected the reproduction of caecilians. They are few of the amphibians that have internal fertilization: the male’s cloaca turns out from the hindgut with special muscles and serves as a copulatory organ, the blood vessels of which, being saturated with blood, give it an elastic (erect) state. The form of such a copulatory apparatus is extremely species-specific. Row African species They even have spines on the cloaca. And some aquatic Potomotyphlus, in addition, also have a specialized grasping organ in the anal region. In representatives of the genus Scolecomorphus, the cloaca is surrounded by clearly visible ridges. All these formations are absent in young organisms, and therefore suggest their participation in the reproduction of adult individuals - they help the male hold the female during mating.
At the row aqueous forms Some semblance of a mating dance was observed.
During the breeding season, males accumulate fat in their bodies, due to which they thicken and become similar to the body shape of pregnant females. Thus, the width of the body of the same species may be different in different physiological states.
Most caecilians lay up to 20 - 30 eggs per wet soil, crevices of the substrate near water, and many species protect the clutch, wrapping their body around it (caring for offspring). The abundant mucous secretions of the skin glands allow them not to dry out. Sometimes some caecilians attach eggs with threads in the form of a bunch of “balloons”. After hatching, the larvae migrate into the water and swim there for several months (up to a year).
One more distinctive feature in the bream is the appearance in the process of embryonic development of seven (and not six) gill slits (seven slits are found only in some cartilaginous fish). The embryos of legless amphibians have external gills in the form of branched bundles (in Ichthyophis spp., Hypogeophis spp.) or plates ( Typhlonectes spp., Siphonops spp.). The larvae have typically fish-like lateral line organs and a dorsal-caudal fin (a fold 1–5 mm high) that disappears after metamorphosis. The exception is aquatic forms, in which the fin remains throughout its life. And some species have a larval fin on their belly.
Found among legless amphibians and viviparous species. These are usually aqueous forms ( Typhlonectes spp.), producing 5 - 8 eggs. After fertilization, their eggs remain in the oviduct, where the developing embryos receive food not through blood, but as if scraping from the walls of the oviduct with larval teeth (which are not identical to the teeth of adult animals) the secretion of specific glands in the form of thick milk. Eating such high-calorie foods, fetuses gain weight very quickly. Pregnancy in caecilians lasts 9-11 months.
Caecilians live in the tropics of America, Africa and Asia (they are not found only in Australia and Madagascar). Many species of legless amphibians are very rare, moreover, they are known from only a few specimens, their way of life is practically not studied. The bulk of legless amphibians are active at night. During the day they hide along the banks of reservoirs, which is why they get caught in fishermen’s nets. In Mexico, legless amphibians can often be found in stables in manure, where a significant number of larvae of various dipterous insects are concentrated.
The main food items for caecilians are termites, earthworms, insect larvae and mollusks. Moreover, species of the genera Afrocaecilia and Boulengerula specialize mainly on termites, and on worms (if they are abundant) - Dermophis spp., and the corpulent caecilian ( Typhlonectes obesus Taylor, 1968) primarily eats beetle pupae. Often, some legless amphibians attack orthoptera insects, butterfly caterpillars, tadpoles and even small lizards ( Dermophis spp., for example). The feeding strategy of caecilians is hiding. But as soon as the victim appears nearby, the amphibian slowly approaches it and grabs it fast movement head, holding prey with well-developed back-curved teeth, sometimes double-pointed. The number of rows of teeth in the lower jaw is an important diagnostic feature. Teeth broken off during hunting are capable of regeneration. One of the most bizarre features of caecilians is the opening of the mouth by raising the skull while the lower jaw is motionless.
Among the enemies of terrestrial caecilians are usually called various snakes(in particular, coral) and birds of prey(for example, the Hen Harrier), and aquatic legless amphibians feed on fish, frogs, freshwater turtles and semi-aquatic mammals.
Caecilians have no special methods of protection from enemies, other than a secretive lifestyle. Movement by bending the body due to a wave of muscle contractions going from head to tail does not save the caecilian. But the inner layers of the skin of some species contain poisonous glands, the secretion of which is dangerous for predators and humans (causes irritation of the nasal mucosa).
The family relationships of legless amphibians with other orders (tailed and tailless amphibians) remain not fully clarified (for example, in terms of the set of chromosomes they are close to Anura, and in terms of the amount of DNA - to Caudata).
Epicrionops bicolor
Rhinatrema bivittatum
Caecilia bannanicus
Caecilia thompsoni
Ichthyophis kohtaoensis
Dermophis mexicanus
A-B Adult female Ichthyophis kohtaoensis(Ichthyophiidae) from Thailand guarding her clutch of early-stage embryos; the species is oviparous with indirect development; the nest is terrestrial; the hatchling larvae make their way to nearby streams where they grow and eventually metamorphose into terrestrial subadults; photo by Alexander Kupfer. C-D. Adult female Boulengerula boulengeri(Caeciliidae) from Tanzania guarding her early-stage embryos in a terrestrial nest; the species is oviparous with direct development (no larval stage); photo by Alexander Kupfer. E-F. Adult Boulengerula taitanus(Caeciliidae) from the Taita Hills, Kenya, guarding her early-stage embryos in a terrestrial nest; the species is oviparous with direct development; photo by Alexander Kupfer.
Information sources:
Dunaev E.A. Diversity of amphibians (based on materials from the exhibition of the Zoological Museum of Moscow State University), 1999.
Jean-Marie Exbrayat Reproductive Biology and Phylogeny of Gymnophiona (Caecilians), 2006
Taxonomy of legless amphibians on
Legless amphibians, or caecilians, says Wagler, “rather than all other reptiles, they have the right to be considered a separate order *, whose body was covered with skin ossifications.
* It has been established that caecilians occupy one of the lowest steps on the “evolutionary ladder” of amphibians. This is evidenced by the presence in the skin of many representatives of bone scales, which they “inherited” from extinct ancestors - stegocephalians (the so-called armored heads).
The number of bone scales in the body of a caecilian can reach 2000, and in the anterior part they are smaller (1-2 mm) than in the posterior part (about 4 mm). In the most mobile areas of the body (in the tail area, for example), they are destroyed, leaving small cavities in the thickness of the skin." Although in appearance they look like snakes or, rather, spindles, in their internal structure they resemble frogs. In appearance they are very similar to amphisbaenus, but differ from them in that their body is naked, there is almost no tail, the anus is round and is located almost at the end of the body, which looks like a cylinder with blunt ends and the same thickness everywhere. Sometimes ring-shaped, closely lying folds of skin are visible on his skin; sometimes the body is smooth and, while the animal is alive, it is covered with sticky mucus**.
* * During the breeding season, male caecilians accumulate fat in their bodies, due to which their bodies thicken and become similar to the body shape of pregnant females.
“All legless people have the same empty, rather large, cone-shaped and somewhat curved teeth, which are attached to the inner edge of the jaws; the tongue is attached with its lower surface to the skin of the mouth and therefore cannot protrude. There are also teeth on the palate, and they are arranged in the form of a horseshoe , as in some fish-like amphibians. As for the lingual bone, it is remarkable in that it has three pairs of arches, which indicates the presence of gills at the beginning of life and, therefore, that the caecilians have a metamorphosis. The external nasal openings are located on the sides of the head. or at the front end, and the internal nasal openings are located on the palate, there are no eyes at all, or they are so covered with the scalp that they are not at all suitable for vision***.
* * * In a number of caecilians, transparent “windows” are usually located above the eyes, and the retina contains only reduced optic rods without cones.
There are always small holes in front of the eyes in which retractable tentacles equipped with a special nerve are placed. The ears, like those of salamanders, are hidden under the skin, do not have an eardrum and, like those of salamanders, consist of a small cartilage lying on an ovoid window.
The structure of the skull is very peculiar: the maxillary bones cover the eye socket in such a way, and the temporal bones cover the temporal socket, that from the outside it seems that the skull is formed by one shield-shaped bone plate*.
* It is interesting that caecilians open their mouths, raising the skull, while the lower jaw is motionless.
The eyes, if they exist, lie on the upper edge of the maxillary bone in a very small elongated depression. The tympanic bone is pushed between the other cranial bones, and the branches of the lower jaw are connected in front by cartilage. The articular surface of the occipital bone is divided in the middle into two parts, just like in frogs. The dorsal vertebrae do not have hemispherical articular surfaces, but have depressions on both sides and are connected by cartilaginous plates lying between the vertebrae. The ribs look like very small appendages; There is no chest bone, pelvis or limbs at all. Only one of the lungs is developed.
The above characteristics, established by Wagler, can still be fully preserved. More detailed description brain and nervous system we find legless amphibians in Waldschmidt; cerebral hemispheres larger than all our amphibians and more similar to the cerebral hemispheres of frogs than salamanders. Latest research significantly expanded the information about these animals: the number of vertebrae can reach up to 250, the liver is divided into many lobes; the male has several seminal glands on each side, and he has a copulatory organ that can be protruded from the inside.
Until recently, very little was known about the history of the development of caecilians. We are indebted to Johann Müller for the message that Ceylon caecilian(Ichthyophis glutinosus) has one gill slits on each side of the neck, which leads to the internal gills. According to Gervais and more detailed instructions from Peters, Typhlonectes compressicauda has caecilians from the northern part South America- there is no trace of gill slits, such as Muller found in the Ceylon caecilian, but the gill apparatus of the tadpole of this animal is very unique. Blood vessels in the gills they do not form loops that penetrate into the branchial papillae, as in other tadpoles, but veins and arteries branch on the surface of the leaf-shaped gill skin. These leaf-shaped external gills strongly resemble bell-shaped ones. respiratory organs in marsupial frog embryos described by Weinland. There is no doubt that the transformation of various caecilians is just as diverse as the transformation of tailless amphibians. For example, Moebius brought with Seychelles several specimens of caecilians of various ages, which have neither the gill slits, nor the leathery ridge on the tail, nor the occipital scars found in tadpoles that breathe with leaf-shaped gills. Dumiril, on the contrary, found on the sides of the neck in one young specimen from Malabar gill slit, which was located slightly higher than that of the Ceylon caecilian, but obviously proved that leaf-shaped gills are not found in this genus. During spawning, caecilians go into the water and lay their eggs there or give birth to live young; Sometimes eggs are laid near water. In some species, eggs are incubated or, according to at least, are protected by the female. The transformation of embryos ends for the most part in an egg; After a short stay in the water, the tadpoles take on the appearance of adult animals and come out onto land.
Graefe reports that the caecilian from East Africa, living on the islands of St. Thomas and Rollas, is often found at an altitude of 400-500 m above the sea surface. But it is also found at an altitude of 900 m. It feeds on insects, larvae, centipedes and earthworms, but also eats snakes from the genus blind. Local residents think that this animal is poisonous, and, according to Wiedersheim's research, it should perhaps be assumed that the glands near the tentacles actually contain poison. The recesses in which the caecilian tentacles are hidden are covered, according to Graefe, with the same skin that covers the tentacle recesses on the outside.
Caecilians are found in tropical countries America, Africa and Asia, but they are not in Australia and Madagascar. They dig the ground and generally lead an underground life, like earthworms, which greatly complicates observations of them. Many of them live in anthills and feed on ants. Their movements consist of slow crawling or swimming, performed by writhing the body. They feed on worms and various other small animals. Nowadays, 14 genera with 37 species of legless amphibians are known, which differ from each other in the development of the eyes, the structure and position of the tentacles, as well as the structure of the skin, whether it has round scales or not *.
* Now all caecilians are divided into 6 families, 33 genera and 163 species.
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This small order includes about 55 species, grouped into 19 genera and one family of caecilians (Coeciliidae). All of them have an elongated worm-like body with frequent circular interceptions and lack not only paired limbs, but also a tail, since the cloaca is located almost at the end of the body.
All caecilians, with the exception of representatives of two South American genera Typhlonectes and Desmophis, living in water, lead an underground life, making passages in damp soil and rotten vegetation.
As an adaptation to the burrowing life of caecilians, one should consider their elongated body shape, the absence of limbs and their girdles, the lower mouth, rudimentary eyes, a rudimentary auditory nerve, the absence of a tympanic membrane and highly developed olfactory organs, as well as internal insemination, due to which the male cloaca has the ability to protrude, performing the role of a copulatory organ.
But along with these highly specialized features, caecilians possess a number of extremely primitive features that bring them closer to ancient armored amphibians. The main primitive features of caecilians are as follows: under their skin they have hidden bone scales, apparently homologous to the scales of ancient armored amphibians, the integumentary bones of the skull are extremely developed, which also, apparently, was inherited by them from armored amphibians, the auditory bone - the stapes - is also articulates with the quadrate, the septum between the atria is not yet complete, and the conus arteriosus lacks the longitudinal valve characteristic of most other groups of amphibians; the vertebral bodies are of the amphicoelous (fish) type; there is a fairly well-developed notochord. A characteristic feature is the presence of short real (lower) ribs.
Along with this, attention is drawn to the extremely strong development of the forebrain in caecilians, which is much larger in them than in all other amphibians.
Caecilians feed on insects, worms and other soil invertebrates. Their reproduction process has little to do with the body of water. Adult caecilians, with the exception of a few aquatic species accidentally falling into the water, they drown. In all eggs, eggs develop outside of water, only the last stages of larval development in a few cases take place in water. Many species, like the Ceylon fish snake (Ichtyophis), wrap large eggs around their moist body. All legless animals have a well-expressed concern for their offspring. Aquatic caecilians are viviparous.
Caecilians are distributed almost exclusively within tropical zone Africa, Asia, Central and South America.
Underground lifestyle with narrow specialization, pronounced care for offspring, aquatic reproduction and significant development the brain distinguishes caecilians from other amphibians.
The two detachments discussed above have those common features that, being primitive in comparison with the dominant order of tailless amphibians, they have a number of progressive features: internal fertilization, caring for offspring. These progressive features, along with the departure of legless animals (Apoda) underground or the return of tailed animals (Urodela) to water bodies, allowed them to survive to this day.
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This small order - about 170 species - includes about 55 species from the family caecilian. All of them have an elongated worm-like body with frequent circular interceptions and lack not only paired limbs, but also a tail, so that the cloaca is located almost at the end of the body. All caecilians, with the exception of representatives of two South American genera Typhlonectes and Desmophis, living in water, lead an underground life, making passages in damp soil and rotten vegetation.
As an adaptation to the burrowing life of caecilians, one should consider their elongated body shape, the absence of limbs and their girdles, a lower mouth, rudimentary eyes, a rudimentary auditory nerve, the absence of an eardrum and highly developed olfactory organs, as well as internal insemination, and therefore, the cloaca of males has the ability to protrude, acting as a copulatory organ.
But along with these highly specialized features, caecilians possess a number of extremely primitive features that bring them closer to ancient armored amphibians. The main primitive features of caecilians are as follows: under their skin they have hidden bone scales, apparently homologous to the scales of ancient armored amphibians, the integumentary bones of the skull are extremely developed, which also, apparently, was inherited by them from armored amphibians, the auditory bone - the stapes - is also articulates with the quadrate, the septum between the atria is not yet complete, the vertebral bodies are of amphicoelous (fish-like) type, there is a fairly well-developed notochord. A characteristic feature is the presence of short true (lower) ribs.
Along with this, attention is drawn to the extremely strong development of the forebrain in caecilians, which is much larger in them than in all other amphibians.
Caecilians feed on insects, worms and other soil invertebrates. Their reproduction process has little to do with the body of water. Adult caecilians, with the exception of a few aquatic species, accidentally fall into water and drown. In all eggs, eggs develop outside of water, only the last stages of larval development in a few cases take place in water. Many types like Ceylon fish snake, wrap large eggs around their wet body. All legless animals have a well-expressed concern for their offspring. Aquatic caecilians are viviparous.
Caecilians are distributed almost exclusively within the tropical zone of Africa, Asia, Central and South America.
An underground lifestyle with narrow specialization, pronounced care for offspring, out-of-water reproduction and significant brain development distinguish caecilians from other amphibians.
The two orders discussed above have the common features that, being primitive in comparison with the dominant order of tailless amphibians, they have a number of progressive features: internal fertilization, care for offspring. These progressive features, along with the departure of legless animals underground or the return of tailed animals to water bodies, have allowed them to survive to this day.
Order Tailless amphibians
Tailless amphibians are the most highly organized and richest group. But, despite their large number, they all, in general, have a very uniform structure. Their body is short and wide, the neck is not pronounced, there is no tail, paired limbs are well developed, and the hind limbs are much larger than the front ones and are used for characteristic jumping movement. The notochord in adults is rudimentary, the caudal spine is in the form of one long bone (urostyle). Ribs, with rare exceptions, are absent. The sternum consists of several parts. There is a collarbone in the shoulder girdle. The ulna and radius are fused in the same way as the tibia and tibia. The carpal and tarsal bones are partially fused. There is a middle ear with an eardrum, sometimes hidden under the skin. Neither gills nor gill slits are ever preserved in adults. There is no copulatory organ, and insemination is external. In the larva, the hind legs erupt first, and then the front legs (in caudates, the appearance of legs proceeds in the reverse order).
The number of species of tailless amphibians is 10 times greater than that of tailed amphibians, and 20 times greater than that of legless ones. There are more than 3,500 species of living anurans.
The anurans include fire toads, midwife toads, African clawed frogs and American pips, spadefoot, crosses, toads, tree frogs, real frogs, short-headed And copepods.
The uniformity in the structure of anurans is associated with an adaptation to movement by jumping, which was primarily inherent in all representatives of this order. The simultaneous push of the hind legs resulted in the development of a shortened, wedge-shaped body and lengthening of the hind limbs. This creates an additional section - the tarsus is like an elastic insert that continues the action of the muscles when jumping. The formation of a narrow pelvis in the form of a characteristic disk is also an adaptation to the fullest use of force when jumping, since with this type of movement it is advisable to have the points of application of forces as shifted as possible. This is also associated with the characteristic lengthening of the iliac bones, which facilitate the transfer of the points of application of forces to the center of gravity of the animal.
Tailless amphibians are mainly terrestrial forms. The number of aquatic forms compared to caudates is very small and does not exceed 15%; just one small family pipovyh consists entirely of people who constantly live in water.
Among terrestrial anurans we find terrestrial, burrowing and arboreal species. Arboreal forms are found quite often among anurans. 6 families out of 12 have woody species, and one of the largest families is tree frog more than 90% consists of woody forms; many types frogs and toads They also lead an arboreal lifestyle. In tree-dwelling species, such as ours, tree frogs, the ends of the fingers are expanded into discs. On these discs an epidermal brush and special glands are formed that secrete a secretion, which allows the animal to stay on vertical surfaces. Some tree frogs of South America and Southeast Asia have extremely developed membranes between the elongated fingers, front and hind legs. These frogs, among which are especially famous copepods, jumping after an insect gliding, they fly up to 10 meters or more from tree to tree.
Burrowing forms, as well as arboreal ones, are very numerous in the order of anurans. They are found among representatives of 6 families, and one family spadefoot consists almost entirely of species leading a burrowing lifestyle. Burrowing species are numerous among true ab And short heads Africa and Australia. Tailless amphibians dig with their hind legs, making alternate movements with their legs to the sides, so that they plunge into the ground with the rear end of their body. The transition to a burrowing lifestyle entails shortening of the limbs, which makes it impossible to make large jumps. This can already be seen in our toads and spadefoots, who often move by walking rather than jumping. Alternating movements of the right and left paws also lead to the formation of a movable joint in the form of sliding articular surfaces between the ilia and sacral vertebrae with a significant expansion of the transverse processes of the latter. Finally, sharp horny “calluses” appear at the base of the first toe, taking on the appearance of a “shovel”, like those of the spadefoot. Skin ossifications on the head, like ours, are associated with a burrowing lifestyle. spadefoot, these formations can take on the bizarre shape of a bone helmet.
The number of aquatic anurans, as mentioned, is very small. In aquatic forms, as in burrowing forms, the hind legs are shortened and a movable articulation of the pelvis with the spine is formed, which is clearly visible, for example, in our fire toads, spending the entire summer period in water. In aquatic forms, there is also a reduction of the tongue up to its complete disappearance, reduction of the eyelids and the appearance of lateral line organs, which occurs in African clawed frogs.
Anurans are very widespread on all continents (except Antarctica) and on all mainland islands, excluding the northernmost ones. It is to these that the general proposition applies that the warmer and wetter the country, the more numerous and diverse its amphibians, which reach their greatest prosperity in moisture-loving tropical forests. It is noteworthy that the most primitive of modern tailless animals is lio-pelma- found in New Zealand, distinguished by the antiquity of its fauna, which is especially richly represented in the forests of South America tree frogs and few in number real frogs, whereas in Africa, on the contrary, there are no tree frogs, and they are replaced here by a variety of tree frogs.
DRAWINGS THAT NEED TO BE COMPLETED IN THE ALBUM
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Lesson topic:
Type Chordata- Chordata.
Order of legless amphibians
Legless amphibians, or caecilians, says Wagler, “rather than all other reptiles, they have the right to be considered a separate order *, whose body was covered with skin ossifications.
* It has been established that caecilians occupy one of the lowest steps on the “evolutionary ladder” of amphibians. This is evidenced by the presence in the skin of many representatives of bone scales, which they “inherited” from extinct ancestors - stegocephalians (the so-called armored heads).
The number of bone scales in the body of a caecilian can reach 2000, and in the anterior part they are smaller (1-2 mm) than in the posterior part (about 4 mm). In the most mobile areas of the body (in the tail area, for example), they are destroyed, leaving small cavities in the thickness of the skin." Although in appearance they look like snakes or, rather, spindles, in their internal structure they resemble frogs. In appearance they are very similar to amphisbaenus, but differ from them in that their body is naked, there is almost no tail, the anus is round and is located almost at the end of the body, which has the appearance of a cylinder with blunt ends and everywhere the same thickness; ring-shaped, closely lying, are sometimes seen on its skin. folds of skin; sometimes the body is smooth and, while the animal is alive, it is covered with sticky mucus**.
* * During the breeding season, male caecilians accumulate fat in their bodies, due to which their bodies thicken and become similar to the body shape of pregnant females.
“All legless people have the same empty, rather large, cone-shaped and somewhat curved teeth, which are attached to the inner edge of the jaws; the tongue is attached with its lower surface to the skin of the mouth and therefore cannot protrude. There are also teeth on the palate, and they are arranged in the form of a horseshoe , as in some fish-like amphibians. As for the lingual bone, it is remarkable in that it has three pairs of arches, which indicates the presence of gills at the beginning of life and, therefore, that the caecilians have a metamorphosis. The external nasal openings are located on the sides of the head. or at the front end, and the internal nasal openings are located on the palate, there are no eyes at all, or they are so covered with the scalp that they are not at all suitable for vision***.
* * * In a number of caecilians, transparent “windows” are usually located above the eyes, and the retina contains only reduced optic rods without cones.
There are always small holes in front of the eyes in which retractable tentacles equipped with a special nerve are placed. The ears, like those of salamanders, are hidden under the skin, do not have an eardrum and, like those of salamanders, consist of a small cartilage lying on an ovoid window.
The structure of the skull is very peculiar: the maxillary bones cover the eye socket in such a way, and the temporal bones cover the temporal socket, that from the outside it seems that the skull is formed by one shield-shaped bone plate*.
* It is interesting that caecilians open their mouths, raising the skull, while the lower jaw is motionless.
The eyes, if they exist, lie on the upper edge of the maxillary bone in a very small elongated depression. The tympanic bone is pushed between the other cranial bones, and the branches of the lower jaw are connected in front by cartilage. The articular surface of the occipital bone is divided in the middle into two parts, just like in frogs. The dorsal vertebrae do not have hemispherical articular surfaces, but have depressions on both sides and are connected by cartilaginous plates lying between the vertebrae. The ribs look like very small appendages; There is no chest bone, pelvis or limbs at all. Only one of the lungs is developed.
The above characteristics, established by Wagler, can still be fully preserved. We find a more detailed description of the brain and nervous system of legless amphibians in Waldschmidt; the cerebral hemispheres are larger than those of all our amphibians and are more similar to the cerebral hemispheres of frogs than of salamanders. Recent research has significantly expanded the information about these animals: the number of vertebrae can reach up to 250, the liver is divided into many lobes; the male has several seminal glands on each side, and he has a copulatory organ that can be protruded from the inside.
Until recently, very little was known about the history of the development of caecilians. We are indebted to Johann Müller for the message that Ceylon caecilian(Ichthyophis glutinosus) has one gill slits on each side of the neck, which leads to the internal gills. According to Gervais and more detailed instructions from Peters, in Typhlonectes compressicauda - caecilians from the northern part of South America - there is no trace of gill slits, which Muller found in the Ceylon caecilian, but the gill apparatus of the tadpole of this animal is very peculiar. The blood vessels in the gills do not form loops extending into the branchial papillae, as in other tadpoles, but veins and arteries branch on the surface of the leaf-shaped gill skin. These leaf-shaped external gills closely resemble the bell-shaped respiratory organs of the marsupial frog embryos described by Weinland. There is no doubt that the transformation of various caecilians is just as diverse as the transformation of tailless amphibians. For example, Moebius brought from the Seychelles several specimens of caecilians of various ages, which have neither gill slits, nor a leathery ridge on the tail, nor occipital scars found in tadpoles that breathe with leaf-shaped gills. Dumiril, on the contrary, found in one young specimen from Malabar a gill slits on the sides of the neck, which was located somewhat higher than in the Ceylon caecilian, but obviously proved that leaf-shaped gills are not found in this genus. During spawning, caecilians go into the water and lay their eggs there or give birth to live young; Sometimes eggs are laid near water. In some species, the eggs are incubated or at least guarded by the female. The transformation of the embryos ends mostly in the egg; After a short stay in the water, the tadpoles take on the appearance of adult animals and come out onto land.
Graefe reports that the caecilian from East Africa, living on the islands of St. Thomas and Rollas, is often found at an altitude of 400-500 m above the sea surface. But it is also found at an altitude of 900 m. It feeds on insects, larvae, centipedes and earthworms, but also eats snakes from the genus blind. Local residents think that this animal is poisonous, and, according to Wiedersheim's research, it should perhaps be assumed that the glands near the tentacles actually contain poison. The recesses in which the caecilian tentacles are hidden are covered, according to Graefe, with the same skin that covers the tentacle recesses on the outside.
Caecilians are found in tropical countries of America, Africa and Asia, but they are not found in Australia or Madagascar. They dig the ground and generally lead an underground life, like earthworms, which greatly complicates observations of them. Many of them live in anthills and feed on ants. Their movements consist of slow crawling or swimming, performed by writhing the body. They feed on worms and various other small animals. Nowadays, 14 genera with 37 species of legless amphibians are known, which differ from each other in the development of the eyes, the structure and position of the tentacles, as well as the structure of the skin, whether it has round scales or not *.
* Now all caecilians are divided into 6 families, 33 genera and 163 species.
Life of animals. - M.: State Publishing House geographical literature.
A. Brem.
1958. See what “Order legless amphibians” is in other dictionaries:
This order includes a total of 56 species, grouped into 19 genera and one family of caecilians (Caeciliidae), which resemble large worms or snakes in appearance. The surface of their elongated, worm-like body is divided by rings... ...
Biological encyclopedia
Legless amphibians Scientific classification ... Wikipedia - (Apoda, Gymnophiona), order of amphibians. Dl. 30-120 cm. Peculiar animals, characterized by both extreme specialization and primitive structure. In connection with adaptation to the underground, burrowing lifestyle, the body of B. z. acquired... ...
Order of amphibians. Length 30-120 cm. No limbs. 3 families (including caecilians), approx. 170 species, in the tropics of Africa, Asia and America. Most live in soil, some in water... Big Encyclopedic Dictionary
Order of amphibians. The length of the worm-like body is 30-120 cm. There are no limbs. 3 families (including caecilians), about 170 species, in the tropics of Africa, Asia and America. Most live in soil, some in water. * * * LEGLESS AMPHIBIDES… … encyclopedic Dictionary
- (Apoda, or Gymnophiona) order of amphibians, including one family of caecilians (Caeciliidae); so called because of their resemblance to large earthworms. About 20 genera (70 species) are known. Distributed in tropical countries of Africa, Asia and... ... Great Soviet Encyclopedia
Caecilians (Apoda, Gymnophiona), order of amphibians. Externally, these animals resemble earthworms and inhabit swampy areas in almost all tropical regions except Madagascar. There are no limbs, no belts, no tail (the cloaca opens to... ... Collier's Encyclopedia
Amphibians (Amphibia), a class of terrestrial vertebrates that usually retain the aquatic larval stage during ontogenesis; b. or m. a close connection with the aquatic environment is characteristic of most species 3. even in adulthood. 3. descended from the ancients lobe-finned fish V… … Biological encyclopedic dictionary
This article is about lizards from the family Anniellidae. Legless lizards are also called spindle lizards, squamopods, worm-like lizards and some others. ? Legless lizards ... Wikipedia