The name of amphibians (amphi-bios) comes from the Greek and means “both lives”. This is because their life cycle takes place between water and land These strange creatures change their way of life and appearance throughout their development. Most are nocturnal and poisonous. Some even gather to sing on rainy nights. Without a doubt, they are one of the most interesting vertebrate animals.
Currently, more than 7,000 species have been described and are distributed throughout almost the entire world, except in places with the most extreme climates. However, due to their particular way of life, they are much more abundant in the tropics. Do you want to know these animals better? Don't miss this article on our site about the different types of amphibians, their classification, names and examples curious.
What are amphibians?
Modern amphibians are non-amniotic tetrapod vertebrate animals, this being the main definition of amphibians. This means that they have a bony skeleton, have four legs (hence the word tetrapods), and lay eggs without protective membranes. Due to the latter, their eggs are very sensitive to dryness and must be placed in water. Aquatic larvae emerge from them and subsequently undergo a transformation process known as metamorphosisThis is how they become adults of semi-terrestrial life. A clear example of this is the life cycle of frogs.
Despite their apparent fragility, amphibians have colonized much of the world and have adapted to different ecosystems and habitats For this For this reason, there are many types of amphibians with enormous diversity. This is due to the large number of exceptions that do not meet the above definition.
Because of their great diversity, it is very difficult to tell what the different types of amphibians have in common. However, we have gathered its most important characters, indicating which ones have exceptions. These are the main characteristics of amphibians:
- Tetrapods: Except for caecilians, amphibians have two pairs of limbs ending in feet. Feet are often webbed with 4 toes, although there are many exceptions.
- Sensitive skin: they have a very fine skin, without scales and sensitive to dryness, so it must always remain moist and at room temperature. moderate.
- Toxicos: amphibians have glands in their skin that produce defensive substances. For this reason, its skin is toxic if ingested or if it comes into contact with the eyes. However, most species pose no threat to humans.
- Skin respiration: Most amphibians breathe through their skin, so they need to keep it moist at all times. Many amphibians complement this type of breathing with the presence of lungs and others have gills throughout their lives. You can learn more about this topic in the article on Where and how amphibians breathe.
- Ectothermy: Your body temperature depends on the environment you are in. For this reason, it is common to see them basking in the sun.
- Sexual reproduction: Amphibians have separate sexes, that is, there are males and females. Both sexes mate for fertilization to take place, which can occur inside the female or outside.
- Oviparous: Females lay aquatic eggs with very thin, gelatinous shells. For this reason, amphibians depend on the presence of water or humidity for their reproduction. Very few amphibians have adapted to arid environments by developing viviparity and do not lay eggs.
- Indirect development: Aquatic larvae hatch from the eggs and breathe through gills. During their development, they undergo a more or less complex metamorphosis in which they acquire the characteristics of adults. Some amphibians develop directly and do not undergo metamorphosis.
- Night: Most amphibians are most active at night, when they come out to hunt and breed. However, many species are diurnal.
- Carnivores: Amphibians are carnivores in their adult state and feed mainly on invertebrates. Despite this, its larvae are herbivorous and consume algae, with few exceptions.
As we mentioned, another of the main characteristics of amphibians is that they undergo a transformation process called metamorphosis. Next, we show a representative image of the metamorphosis of amphibians.
Classification of amphibians
Amphibians belong to the class Amphibia, which is divided into three orders:
- Gymnophiona Order
- Order Urodela
- Order Anura
Each one of the orders includes families and subfamilies that includes the different amphibian species. So, next we will see the types of amphibians found in each group.
Types of amphibians and their names
There are three types of amphibians:
- Caecilians or legless (order Gymnophiona).
- Salamanders and newts (order Urodela).
- Frogs and toads (order Anura).
Caecilians or apodes (Gymnophiona)
Caecilians or apods are about 200 species that are distributed throughout the tropical forests of South America, Africa and Southeast Asia. They are amphibians with a vermiform appearance, that is, with elongated and cylindrical shapeUnlike other types of amphibians, caecilians do not have legs and some have scales on their skin.
These strange animals live buried under moist soil, so many are blind. Unlike anurans, males have a copulatory organ, so fertilization occurs inside the female. The rest of their reproductive process is very different in each family and even in each species.
Salamanders and newts (Urodela)
The order Urodelos comprises about 650 species. They are characterized by having a tail throughout their lives, that is, larvae do not lose their tail during metamorphosis. In addition, their four legs are very similar in length, so they move by walking or climbing. As in caecilians, fertilization of the eggs occurs inside the female through copulation.
The traditional division into salamanders and newts has no taxonomic value. However, salamanders are usually called species that have a fundamentally terrestrial way of life. They often live in moist soils and only go to the water to reproduce. Newts, meanwhile, spend considerably more time in the water.
Frogs and Toads (Anura)
The name “a-nuro” means “without tail”. This is because the larvae of these amphibians, known as tadpoles, lose this organ during metamorphosis. Therefore, adult frogs and toads lack tails. Another distinguishing characteristic is that its hind legs are longer than the front ones and they move by jumping. Unlike other types of amphibians, fertilization of the eggs occurs outside the female.
As in urodeles, the differences between frogs and toads are not based on genetics and taxonomy, but on human perception. Robust anurans are known as toads, which often have more terrestrial habits, so their skin is drier and more warty. Frogs, meanwhile, are graceful-looking animals, skilled jumpers and sometimes climbers. Their life is usually more associated with aquatic environments.
Examples of amphibians
In this section we show you some examples of amphibians. Specifically, we have selected some of the curious species. In this way, we will be able to better understand the highly variable characteristics that appear in the different types of amphibians.
- Mexican caecilian or tapalcua (Dermophis mexicanus): these caecilians are viviparous. Their embryos develop inside the mother for several months. There they feed on internal secretions produced by their mother.
- Koh Tao Caecilian (Ichthyophis kohtaoensis): This is a Thai caecilian that lays its eggs on land. Unlike most amphibians, the mother cares for the eggs until they hatch.
- Amphiumas (Amphiuma spp.): These are three species of very elongated, cylindrical aquatic amphibians with vestigial legs. In them, A. tridactylum has three toes, A. means has two and A. pholeter only has one. Despite their appearance, they are not caecilians, but urodeles.
- Proteus (Proteus anguinus): This urodele is adapted to live in the dark of some European caves. For this reason, adults have no eyes, are white or pinkish, and live in water throughout their lives. In addition, they are elongated, have a flat head and breathe through gills.
- Gallipato (Pleurodeles w alt): it is a European urodele that can reach 30 centimeters in length. Along its side is a row of orange spots that coincide with the edges of its ribs. When they feel threatened, they make them stand out, threatening potential predators.
- Hairy Frog (Trichobatrachus robustus): Despite their appearance, furry frogs do not have hair, but rather extensions of skin vascularized. These increase the gas exchange surface, so that they can capture more oxygen.
- Suriname Toad (Pipa pipa): This Amazonian toad is characterized by its enormously flattened body. The female has a kind of web on her back. The eggs sink and adhere to it during copulation. From them, larvae do not come out, but small young toads.
- Mount Nimba Toad (Nectophrynoides occidentalis): This is a viviparous African toad. The females give birth to young that have the same appearance as an adult. Direct development is a reproductive strategy that allows them to be independent of water bodies.
Curiosities of amphibians
Now that we know all the types of amphibians, let's look at some of the more interesting features that appear in some species.
Animal aposematism
Many amphibians have very striking colorations. They are used to inform possible predators about their poison. These identify the intense color of the amphibians with a danger, so they do not eat them. Thus, both avoid an upset.
A very curious example is that of the fire-bellied toads (Bombinatoridae). These Eurasian amphibians are characterized by having heart-shaped pupils and a red, orange or yellow belly. When disturbed, they will turn around or show the color of their lower legs in a posture known as "unkenreflex." In this way, predators observe the color and associate it with danger.
Better known are the arrowhead frogs (Dendrobatidae), highly poisonous and striking anurans that live in the Neotropics. You can learn about more aposematic species in this article on Animal Aposematism, including other types of amphibians.
Pedomorphosis
Some urodeles present paedomorphosis, that is, they maintain their juvenile characteristics when they are adults. It occurs when physical development slows down, so sexual maturity appears when the animal still has the appearance of a larva. This process is known as neoteny and it is what occurs in the Mexican salamander (Ambystoma mexicanum) and in the proteus (Proteus anguinus).
Pedamorphosis may also be due to acceleration of sexual maturity In this way, the animal acquires the ability to reproduce while it still has a larval appearance. It is a process known as progenesis and occurs in species of the genus Necturus, endemic to North America. Like the axolotl, these urodeles keep their gills and live permanently in the water.
Endangered amphibians
Some 3,200 amphibian species are in danger of extinction, that is, almost half In addition, it is believed that more than 1,000 Endangered species have yet to be discovered due to their scarcity. One of the main threats to amphibians is the chytrid fungus (Batrachochytrium dendrobatidis), which has already made hundreds of species extinct.
The rapid expansion of this fungus is due to human actions, such as globalization, animal trafficking and the irresponsible release of pets. In addition to being disease vectors, exotic amphibians quickly become invasive species. They are often more voracious than native species, displacing them from their ecosystems. This is the case of the African clawed frog (Xenopus laevis) and the American bullfrog (Lithobates catesbeianus).
On top of that, the disappearance of their habitats, such as freshwater bodies and humid forests, is causing the decline of the amphibians. It is due both to climate change and to the direct destruction of aquatic habitats and deforestation.
