Amphibia - Overview, Classifications, Defination

Amphibians are cold-blooded animals that live on both water and land, depending on their different stages of life. They begin their life as aquatic larvae and respire with the help of gills. Afterwards, they transform into adults who respire by means of lungs. They rely on their environment for survival.

This Story also Contains

1. What are Amphibians?
2. Classification of Amphibia
3. Amphibians Examples
4. Life Cycle of Amphibians
5. Adaptations and Physiology of Amphibians
6. Ecology and Habitat of Amphibians
7. Recommended Video on Amphibians

Their name reflects their dual nature of life- ‘amphi’ meaning both and ‘bios’ meaning life. This group of animals include frogs, toads, salamanders, and caecilians. The topic Amphibia is from the chapter Animal Kingdom in Biology.

What are Amphibians?

Amphibians are vertebrate animals characterised by living partly on land and partly in water in the different stages of their life cycles. They undergo metamorphosis from aquatic larvae to terrestrial adult stages. They form important links in ecosystems as both predators and prey, contribute to biodiversity by inhabiting wide and varied environments, and become indicators of environmental quality because of their sensitivity to habitat alteration.

Also Read:

• Frogs
• Urochordata
• Biological Classification

Classification of Amphibia

Amphibians are classified into different orders based on features like limb structure, tail presence, and body shape. The major groups include Anura (frogs and toads), Caudata (salamanders), and Gymnophiona (caecilians). This classification helps in understanding their diversity and evolutionary relationships.

The orders of Amphibia are:

Anura (Frogs and Toads)

• Anurans differ from others by their long hindlimbs, modified for jumping, and have no tail in the adult stage. They have a wide mouth and prominent eyes.

• Frogs and toads occupy a wide variety of ecosystems, from rainforests and wetlands to arid deserts and mountainous locales.

• They mostly breed in water, laying eggs that hatch into tadpoles, which go through metamorphosis into adult frogs or toads.

• Anurans are major predators of insects and other small invertebrates, while they become the prey of many larger animals.

Caudata (Salamanders and Newts)

• The Caudates are elongated, with a tail and often retain a lizard-like appearance of the body. They possess limbs of equal size and a distinct head.

• They inhabit humid environments, forests, swamps, and streams. They are mainly distributed in the Northern Hemisphere.

• Most salamanders lay eggs in water whose larvae are similar to adults but with external gills, some species have a direct development where the young hatch as miniature adults.

• Salamanders and newts include predation and nutrient cycling during their life cycles.

Gymnophiona (Caecilians)

• Caecilians are limbless, elongate amphibians that are somewhat earthworm or snake-like in appearance.

• Their bodies are segmented in appearance and often have very small eyes, reduced sometimes to being covered entirely with skin.

• They occur mainly in the tropics, in damp earthy or aquatic environments. Therefore, due to their underground nature, their lives are less spectacularly visible and less studied.

• Some caecilians are egg-laying while others are viviparous. Most have parental care in which the mother's skin produces secretions utilized as food for young, some have even brood layers of skin.

• Caecilians, being burrowers, aerate soils and help in regulating the number of invertebrates dwelling in soils.

• Their activities played a very significant role in the maintenance of soil health and the dynamics of ecosystems.

Characteristics of Amphibians

Amphibians are cold-blooded vertebrates with moist, permeable skin and a life cycle that typically includes both aquatic and terrestrial stages. They breathe through lungs, skin, and gills at different stages of life. Most amphibians undergo metamorphosis from larval to adult form. Some general characteristics of Amphibians are:

• Amphibians have smooth and moist skin with mucous glands to aid in respiration and water absorption.

• Most amphibians possess four modified limbs, which are meant to undertake the more specialised modes of locomotion, for instance, swimming in water types and fast hopping on the ground.

• They have digestive organs like the mouth, oesophagus, stomach, and intestines, which are modified with a view to carnivorous and herbivorous diets.

• They manifest cutaneous respiration through the skin and display lungs or gills depending on the phase of life and habitat.

• It contains a double-loop blood circulation with a three-chambered heart, where oxygenated and deoxygenated blood is pumped efficiently.

• The nervous system consists of the brain and spinal cord, which control sensory perception and motor functions.

Amphibians Examples

Life Cycle of Amphibians

The life cycle of amphibians usually starts with eggs laid in water, which hatch into larvae like tadpoles. These larvae then undergo metamorphosis to become terrestrial adults. This life cycle reflects their need for both aquatic and land environments.

• Most amphibians lay eggs in aquatic environments and then fertilise them outside their bodies.

• Amphibians undergo metamorphosis from aquatic larvae, which are tadpoles with gills, into terrestrial adults with lungs.

• The life stages of amphibians are embryonic larval form, and then they metamorphose into adults, all morphologically adapted to the environment and needs in those stages.

Diagram of Amphibian (frog) life cycle

The diagram given below shows the life cycle of an amphibian, mainly a frog, with different life stages.

Adaptations and Physiology of Amphibians

Amphibians have adaptations like cutaneous respiration, webbed feet, and strong limbs for jumping and swimming. These are the adaptations to survive in moist environments. The adaptations in the amphibians are described below:

Ecological Adaptations

• Cutaneous respiration plays the role of gas exchange through the skin of amphibians, which is quite important to species without lungs or that are at the aquatic stage.

• As ectotherms, they cannot maintain their body temperature but depend on the external environmental conditions.

• The animal shows great tolerance to changes in the environment.

Physiological Adaptations

• They have evolved adaptive mechanisms in their skin anatomy to maintain the ever-changing body's water balance and osmoregulation.

• With behavioural adaptations such as hibernation and aestivation, they pass through hostile periods and thus ensure perpetual survival in their wide range of habitats.

Ecology and Habitat of Amphibians

Amphibians are generally seen in moist and shady areas, near freshwater places like ponds, rivers, and wetlands. They play important ecological roles like controlling insect populations and serving as bioindicators of environmental health

• They range in habitats from terrestrial to aquatic and even semi-aquatic, making a home in forests, deserts, and less hostile freshwater bodies.

• They are important in ecosystems in terms of predator-prey dynamics—amphibians are in turn predators of insects and other small vertebrates, and become the prey of larger animals.

• This demonstrates a significant role in nutrient cycling and energy transfer in food webs.

Also Read

Recommended Video on Amphibians