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9.3.1. Amphibians

Amphibian class

The amphibians (from the Greek, amphi, "both" and bios, "life", which means "both lives" or "both ways") are a class of anamniotes vertebrates (without amnion, such as fish), tetrapodsectotherms, with gill respiration during the larval phase and pulmonary when reaching the adult stage.

Amphibians have not managed to become independent of water, since their larvae, the tadpoles, are aquatic, but when they reach adulthood, with metamorphosis, although they can live on land, they need to live in humid areas to avoid dehydration.

Amphibians are tetrapods, with four limbs adapted to the terrestrial environment.

Larvae of amphibians are herbivores, but when amphibians are adults they are carnivores. They are able to catch their prey (insects, other invertebrates,...) with their sticky tongue and swallow them without chewing.

Amphibian larvae have gill respiration. Adults, on the other hand, have pulmonary and cutaneous respiration . For this reason, they have very thin skin, without scales or feathers or hair, and it is always moist so that gaseous exchange can take place . Some species have glands that secrete poison.

Your heart is divided into two atria and one ventricle.

They are ectotherms, so they cannot live in very cold places, as they go dormant when it is very cold.

Reproduction in amphibians is sexual  with external fertilization. That is, the union of eggs and sperm occurs outside the female's body.

Amphibians are oviparous, they reproduce by laying eggs in water or in very humid places to avoid drying out.

Types of amphibians

The most common amphibians belong to two large Orders:


Anurans are amphibians without tails (in Greek, a is negation, and ourá means tail) when they are adults. They are known as frogs and toads.

His body is short and wide.

The hind legs are longer than the front ones, since they are adapted to be able to jump.

They have an extensible and sticky tongue to be able to hunt at a certain distance.

Some species have interdigital webs on the hind legs to facilitate swimming.


Urodeles have an elongated body with a tail. All its legs are short and the same length.

The urodeles are the salamanders, the newts and the gallipatos.

Caecilians, other amphibians

There are other types of amphibians, such as the Cecilias, which do not have legs (they are legless) and live underground.

Or the Proteus, which have a body similar to a snake and have small legs.

Other curious amphibians are the Cecilias, which lack legs (legless) and live underground.

CeciliaBy Pierootiura [GFDL or CC BY-SA 4.0 ], from Wikimedia Commons

Differences between anuran amphibians and urodeles
anuran amphibians urodeles amphibians
short body elongated body
they have no tail Have tail
The hind legs are longer than the front legs. All legs are short and the same length.
interdigital membranes on hind legs They do not have interdigital membranes.

Example: frogs and toads

Example:  salamanders,  newts  and  gallipatos


Amphibians, in their larval stage, live in water and are similar to fish. Instead, when they are adults, they live outside the water and are similar to terrestrial vertebrates.

Metamorphosis is the set of major morphological and physiological changes that occur in an amphibian from when it is a tadpole until it becomes an adult individual.

The development of amphibians begins inside an egg that contains the necessary food for the first stages of life. When the food runs out, the embryo breaks the egg cover (it is not hard) and comes out as a tadpole (larval phase). The tadpole is herbivorous and breathes through gills. Later, during metamorphosis, the tadpole undergoes a series of changes. His hind legs appear first, then his front legs. The mouth gets wider, the eyes get bigger, and the tail disappears. In addition, the adult frog is carnivorous and breathes through lungs that allow it to take oxygen from the air, not from the water . like when he had gills.

Curiosity: The poison of frogs

Batrachotoxin (from the Greek batrachos, meaning frog, and toxine, meaning poison) is a toxic substance secreted through the skin by some frogs of the genus Phyllobates and Dendrobates and some birds (PitohuiIfrita kowaldiColluricincla megarhyncha).

The "dart frogs" (Phyllobates terribilis) are considered to be the most poisonous vertebrate known. In fact, the indigenous people of Colombia used this substance to poison their arrows. But no vertebrate can synthesize this toxin de novo , instead it is produced by the beetles on which they feed. Frogs transport this substance to their skin, where they expel it.