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, that is, they depend on external sources of heat to control their internal balance. In addition, they are amniotics, 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 occurred over millions of years. Their ancestors lived about 350 million years ago , in the late Devonian, and their bodies were robust, with broad, flattened legs and many fingers.

These were the Acanthostega and Icthyostega, which were the predecessors of all the tetrapods that we know today. Amphibians have a worldwide distribution, although they are not present in the desert regions, in the polar and antarctic zones and in some oceanic islands.

What are amphibians?

Amphibians are vertebrate tetrapod animals, that is, they have bones and four limbs. It is a group of very peculiar animals, as they undergo a metamorphosis that allows them to move from the larval stage to the adult stage, which also means that, throughout life, 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 the Cecilia, whose body resembles that of the 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 have no tail and are the best known. Some examples are frogs and toads;

Within the characteristics of amphibians, the following stand out:

The metamorphosis of amphibians

Amphibians have certain peculiarities in their ways of life. Unlike the rest of the tetrapods, they undergo a process called metamorphosis, during which the larva, that is, the tadpole, becomes an adult and passes from branchial to pulmonary respiration. During this process, numerous structural and physiological changes occur, through which the organism prepares itself to move from aquatic to terrestrial life.

The amphibian’s egg is deposited in water; therefore, when the larva hatches, it has gills to breathe, a tail and a circular mouth to eat. After some time in the water, it will be ready for metamorphosis, in which it will undergo dramatic changes ranging from the disappearance of the tail and gills , as in some salamanders (Urodelos), to profound changes in organic systems, as occurs in frogs ( Frogs). The following also happens:

Development of the anterior and posterior extremities;
Development of a bone skeleton;
Lung growth;
Differentiation of ears and eyes;
Changes in the skin;
Development of other organs and senses;
Neuronal development;

However, some species of salamanders may not need metamorphosis and reach the adult state still with characteristics of larvae, such as the presence of gills, making them look like a small adult. This process is called neotenia.

The skin of amphibians

All modern amphibians, that is, Urodelos or Caudata (salamanders), Anurans (frogs) and Gimnofiona (cecilies), are jointly called Lissanphibia, and this name derives from the fact that these animals have no scales on their skin , so she is “naked “. They do not have another dermal coating like the rest of vertebrates, either by hair, feathers or scales, with the exception of cecilies, whose skin is covered by a type of “dermal scale”.

On the other hand, their 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 abrasion from the environment and against other individuals, acting as your first line of defense.

Many species, such as dendrobatids (poisonous frogs), have very bright colors that allow them to give a “warning” to their predators, since 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 coloring.

Skeleton and ends of amphibians

This group of animals has a great variation in terms of their skeleton in relation to other vertebrates. During their evolution, they lost and modified many bones of the forelimbs, but their waist, on the other hand, is much more developed.

The front legs have four fingers and the rear legs five, and are elongated for jumping or swimming , except for cecilia, which have lost 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 feeding

Answering the question about what amphibians eat is a little tricky, since amphibians feed varies according to age , being able to feed on aquatic vegetation during the larval stage and small invertebrates in adulthood, 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 is the bullfrogs (found within the group of frogs), who are opportunistic hunters and can often even suffocate themselves when trying to swallow prey that are too big.

Amphibian breathing

Amphibians have gill (in their larval phase) and cutaneous respiration , thanks to their thin and permeable skin, which allows them to make the gas exchange. However, adults also have lung breathing and, in most species, combine the two modes of breathing throughout life.

On the other hand, some species of salamanders completely lack pulmonary respiration, so they use only gas exchange through the skin, which is usually folded, so that the exchange surface increases.

Other characteristics of amphibians

In addition to the previously mentioned characteristics, amphibians are also differentiated by the following:

Three-heart heart: they have a three-heart heart, with two atria and one ventricle, and a double circulation through the heart. Your skin is highly vascularized.
They perform services in the ecosystem: 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 skins. This caused a decrease in their populations 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, about 700 species of urodels and more than 200 correspond to gymnophions.
Endangered: a significant number of species are vulnerable or endangered due to the destruction of their habitat and a disease called chytridiomycosis, caused by a pathogenic chytrid fungus, Batrachochytrium dendrobatidis , which is drastically destroying its populations.