Content
- What are amphibians?
- Types of amphibians
- Amphibian Characteristics
- The metamorphosis of amphibians
- amphibian skin
- Amphibian Skeleton and Extremities
- Amphibian mouth
- Amphibian feeding
- Amphibian breathing
- Amphibian reproduction
- Other characteristics of amphibians
Amphibians make up the most primitive group of vertebrates. Their name means "double life" (amphi=both and bios=life) and they are ectothermic animals, meaning they depend on external sources of heat to control their internal balance. Also, they are amniotes, like fish. This means that your embryos are not surrounded by a membrane: the amnion.
On the other hand, the evolution of amphibians and their passage from water to land took place over millions of years. Your ancestors lived about 350 million years ago, at the end of the Devonian, and their bodies were robust, with long legs, flat and with many fingers. These were Acanthostega and Icthyostega, which were the predecessors of all the tetrapods we know today. Amphibians have a worldwide distribution, although they are not present in desert regions, in the polar and Antarctic zones, and on some oceanic islands. Keep reading this PeritoAnimal article and you will understand all the amphibian characteristics, their peculiarities and lifestyles.
What are amphibians?
Amphibians are tetrapod vertebrate animals, that is, they have bones and four limbs. This is a very peculiar group of animals, as they undergo a metamorphosis that allows them to pass from the larval stage to the adult stage, which also means that, throughout their lives, they have different breathing mechanisms.
Types of amphibians
There are three types of amphibians, which are classified as follows:
- Amphibians of the order Gymnophiona: in this group, there are only caecilians, whose body resembles that of worms, but with four very short limbs.
- Amphibians of the Caudata order: are all amphibians that have tails, such as salamanders and newts.
- Amphibians of the order Anura: they do not have a tail and are the best known. Some examples are frogs and toads.
Amphibian Characteristics
Among the characteristics of amphibians, the following stand out:
The metamorphosis of amphibians
Amphibians have certain peculiarities in their way of life. Unlike the rest of the tetrapods, they go through a process called metamorphosis, during which the larva, ie the tadpole, becomes turn into adult and passes from branchial respiration to pulmonary respiration. During this process, numerous structural and physiological changes occur, through which the organism prepares itself to pass from aquatic to terrestrial life.
The amphibian egg is deposited in water; therefore, when the larva hatches, it has gills to breathe, a tail, and a circular mouth to eat. After a while in the water, it will be ready for metamorphosis, in which it will undergo dramatic changes ranging from disappearance of the tail and gills, as in some salamanders (Urodelos), to profound changes in organic systems, as in frogs (Anurans). O next also happens:
- Development of anterior and posterior extremities;
- Development of a bony skeleton;
- Lung growth;
- Differentiation of ears and eyes;
- Skin changes;
- Development of other organs and senses;
- Neuronal development.
However, some species of salamanders can don't need the metamorphosis and reach the adult state still with larval characteristics, such as the presence of gills, making them look like a small adult. This process is called neoteny.
amphibian skin
All modern amphibians, ie Urodelos or Caudata (salamanders), Anuras (toads) and Gimnophiona (caecilians), are collectively called Lissanphibia, and this name derives from the fact that these animals have no scales on the skin, so she is "naked". They do not have another dermal lining like the rest of vertebrates, whether hair, feathers or scales, with the exception of caecilians, whose skin is covered by a type of "dermal scale".
On the other hand, your skin is very thin, which facilitates their skin breathing, is permeable and is provided with rich vascularization, pigments and glands (in some cases toxic) that allow them to protect themselves against environmental abrasion and against other individuals, acting as their first line of defense.
Many species, such as dendrobatids (poison frogs), have very bright colors that allow them to give a "warning" to their predators, as they are very impressive, but this coloration is almost always associated with poisonous glands. This in nature is called animal aposematism, which is basically a warning color.
Amphibian Skeleton and Extremities
This group of animals has a wide variation in terms of its skeleton in relation to other vertebrates. During their evolution, they lost and modified many bones of the forelimbs, but his waist, on the other hand, is much more developed.
The front legs have four toes and the hind legs, five, and are elongated to jump or swim, except in caecilians, which lost their hind limbs due to their lifestyle. On the other hand, depending on the species, the hind legs can be adapted for jumping and swimming, but also for walking.
Amphibian mouth
The mouth of amphibians is characterized by having the following characteristics:
- Weak teeth;
- Large and wide mouth;
- Muscularized and fleshy tongue.
Amphibian tongues facilitate their feeding, and some species are able to protrude out to capture their prey.
Amphibian feeding
Answering the question about what amphibians eat is a little tricky, as amphibians feed varies with age, being able to feed on aquatic vegetation during the larval stage and small invertebrates in the adult stage, such as:
- Worms;
- Insects;
- Spiders.
There are also predatory species that can feed on small vertebrates, such as fish and mammals. An example of this are the bullfrogs (found within the group of frogs), which are opportunistic hunters and often can even suffocate when trying to swallow prey that are too large.
Amphibian breathing
Amphibians have gill breathing (in its larval stage) and skin, thanks to their thin and permeable skin, which allows them to exchange gas. However, adults also have lung breathing and, in most species, they combine the two modes of breathing throughout their lives.
On the other hand, some species of salamanders completely lack lung respiration, so they only use gas exchange through the skin, which is usually folded so that the surface of the exchange increases.
Amphibian reproduction
Amphibians present separate sexes, that is, they are dioecious, and in some cases there is sexual dimorphism, which means that male and female are differentiable. Fertilization is mainly external to anurans and internal to urodelus and gymnophionas. They are oviparous animals and their eggs are deposited in water or moist soil to prevent dryness, but in the case of salamanders, the male leaves a packet of sperm in the substrate, called spermatophore, to be collected later by the female.
Amphibian eggs are laid inside frothy masses produced by parents and, in turn, can be protected by a gelatinous membrane which also protects them against pathogens and predators. Many species have parental care, although they are rare, and this care is limited to carrying the eggs inside the mouth or the tadpoles on their back, and moving them if there is a predator nearby.
Also, they have a sewer, as well as reptiles and birds, and it is through this channel that reproduction and excretion take place.
Other characteristics of amphibians
In addition to the aforementioned characteristics, amphibians are also distinguished by the following:
- tricavitary heart: they have a tricavitary heart, with two atria and one ventricle, and a dual circulation through the heart. Your skin is highly vascularized.
- Perform ecosystem services: since many species feed on insects that can be pests for some plants or vectors of diseases, such as mosquitoes.
- They are good bioindicators: some species can provide information about the environment in which they live, as they accumulate toxic or pathogenic substances in their skin. This caused their populations to decrease in many regions of the planet.
- Great diversity of species: there are more than 8,000 species of amphibians in the world, of which more than 7,000 correspond to anurans, around 700 species of urodelos and more than 200 correspond to gymnophionas.
- Endangered: a significant number of species are vulnerable or endangered due to habitat destruction and a disease called chytridiomycosis, caused by a pathogenic chytrid fungus, Batrachochytrium dendrobatidis, which is drastically destroying their populations.
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