THE 3 CLASSES OF AMPHIBIANS AND THEIR CHARACTERISTICS - BIOLOGY - 2025

The most important classes of amphibians that exist today are divided into three large groups: the Anura order, Caudata order and Gymnophiona order.

Amphibians are vertebrate animals characterized by the fact that their breathing system undergoes a modification throughout their life. It begins as branchial (through the bronchi) in the larval stage, and pulmonary (through the lungs) in the adult stage.

The word amphibian comes from the Greek "amphibia" which means "both lives" or both types of life, making clear reference to this breathing capacity that allows them to live both in water and on land.

Although these animals spend most of their life on land, they are born in water, return to it to lay their eggs and are capable of being submerged for a long time thanks to the fact that they can breathe through the skin.

Amphibian skin is not covered by hairs or feathers like that of other vertebrates, but is completely bare and also has a large number of glands that secrete a slimy substance that keeps them permanently moist, even out of the water.

It is said that they are the oldest vertebrate animals on Earth and have undergone a very slow evolution over millions of years, during which a large number of specimens have disappeared. Today, it is estimated that there are more than 6,300 species of amphibians in the world.

Main classes of amphibians and their characteristics

The aforementioned amphibian groups are explained in more detail below:

1- Anurans (toads and frogs)

In ancient Greek, Anuro means "without a tail" and it is precisely this that characterizes this group and differentiates it from the rest.

The body of these species is short and wide and their hind legs are usually more developed than the front legs, which is why they stand out for their ability to make great jumps.

The size of the amphibians in this group can vary from the truly small (less than one centimeter) to some that exceed 30 centimeters in length, such as the Goliath frog, the largest in the world.

This is the largest and most diverse group of amphibians and it is estimated that there are more than 5,400 species, although it is also true that many have become extinct or are in danger of extinction.

Although frogs and toads belong to different families (Pelophylax and Bufonidae, respectively), both terms are often confused, reclassifying them in a rather arbitrary and unscientific way.

In this way, frogs are located as those amphibians with smooth and humid skin that live mostly in water, being the toads, according to this vision, those with the roughest and darkest skin, fatter and slower and that are seen with more often in moist soil.

Other characteristics of anurans

1- Big heads and wide mouths.

2- Bulging eyes with eyelids.

3- Protractile tongue (which projects outward).

4- Four toes on the front legs and five on the back legs.

5- Interdigital membrane.

2- Caudates (salamanders and newts)

Unlike anurans, caudates do have a prominent tail that, together with their rough skin, which in some cases imitates scales or changes color, gives it a somewhat prehistoric appearance.

They have elongated bodies with flat, broad skulls. Its size can vary between 30 centimeters and one meter in length, as is the case with the giant salamander of Japan, the largest known so far.

A few species of salamanders have internal fertilization, contradicting that of common amphibians.

Also, a small part of the approximately 550 existing species inhabit the Southern Hemisphere (north of South America), since the vast majority inhabit the Northern Hemisphere, specifically in the United States of North America.

Caudates can be confused by common people with lizards, but they differ from these in that they do not have scales.

Other characteristics of the caudates

1- They have 4 short and generally equal legs, although in some cases the hind legs are less developed or almost non-existent.

2- They have teeth in both jaws.

3- They can regenerate a mutilated limb, such as the tail.

4- They lack a middle ear (another difference compared to anurans).

5- The larvae are very similar in shape to adults.

3- Gymnofions or apodes (caecilians)

Gymnophiona is Greek for "bare head" and is the least diverse group of amphibians.

They are characterized by their worm shape (vermiforms) and by their protractile tentacles, one on each side of the head, where their sense of smell lies, essential to get food, since their eyes are very small and their sight is limited or null..

They do not have limbs or waist, and they inhabit only the very humid regions of the tropics, usually below the ground or directly under water. They are popular in India, South China, Central and South America. They do not exist in Europe or Oceania.

Its size can vary from 1 centimeter to one and a half meters in length, along which some 200 ring-shaped vertebrae line, a very primitive skeletal structure.

Some are oviparous and some are viviparous (the eggs hatch within the female's body) with internal fertilization.

There are approximately 200 known species of caecilians. Due to their appearance, they are often confused with earthworms.

Other characteristics of gymnofions

1- Flat head and rudimentary eyes that sometimes remain closed.

2- Small teeth and jaw located under the head.

3- Solid skull that makes it easy for you to dig underground.

4- Scrolling in a wavy shape, thanks to its ringed structure.

5- They are carnivores; Depending on their size, they can eat snakes and other amphibians.

Other general characteristics of amphibians

1- They have legs instead of fins.

2- Naked and damp skin.

3- They are cold-blooded animals, that is, their body temperature adapts to that of the environment in which they are found.

4- branchial respiration when they are larvae and pulmonary when they are adults.

5- They are carnivores (they feed on invertebrates such as insects, crustaceans or arachnids).

6- They are oviparous.

7- Its fertilization is external (the eggs are laid in the water) in most cases.

References

1. Amphibians Recovered from biodiversity.gob.mx.
2. Amphibians. Recovered from portaleducativo.net.
3. Anura. Amphibian Order. Recovered from britannica.com.
4. Nature. Caudata. Recovered from diarium.usal.es.
5. Caudata Scopoli. 1777. Recovered from asturnatura.com.
6. The caecilians. Recovered from bgreenproject.wordpress.com.
7. The caecilians or caecilians. A legless amphibian that is mistaken for the earthworm. Recovered from paxala.com.
8. Amphibia, Caudata and Gymnophiona. Recovered from wikipedia.org.