Amphibia

Introduction to Amphibia

The word ‘amphibian’ means “two lives” because all amphibians spend at least some part of life in the water, and another part of their lives on land. Amphibians are the name for a large group of animals, which are made of frogs, toads, salamanders that can be found on every continent except for Antarctica. They are vertebrates, which means they have backbones, and just like reptiles, they are cold-blooded. Unlike reptiles,  amphibians do not have scaly skin. Instead, their skin is usually smooth and moist. Water is the place where amphibians usually lay their eggs. Their eggs are protected by jelly-like substances.


Classification of Amphibian

Living members of amphibians are grouped under three orders.

Order 1. Gymnophiona

  • Limbless blind, elongated and worm-like

  • The tail is short or absent 

  • Limb-girdle is absent

  • Example- Caecilians


Order 2. Urodela, it is Divided into Five Suborders

  1. Cryptobranchoidea

  • Most primitive, permanently aquatic

  • Adult without eyelid

  • External fertilization occurs

  • Example- Cryptobranchus

  1. Ambystomoidea

  • Living on land

  • Adult with eyelid

  • Internal fertilization

  • Example- Ambystoma

  1. Salamandridae

  • Opisthocoelous Vertebrates are present

  • Teeth are found on the roof palate

  • Internal fertilization.

  • Example- Salamander

  1. Provider

  • Living as aquatic animals

  • Without eyelids and lungs

  • Cartilaginous skull

  • Example - Proteus

  1. Meanies

  • Aquatic representing permanent larvae

  • Without eyelids

  • Horny jaws

  • Example- Meantes


Order 3. Anura

  • Amphibian without tail

  • Adult without gills

  • Internal fertilization

  • Example- Bufo 


Scientific Classification

Kingdom – Animalia

Phylum – Chordata

Clade- Batrachomorpha

Class- Amphibia

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Characteristics of class Amphibia

General Characters 

  • Amphibians are those animals that can live in the land as well as on water.

  • Amphibians  are dual-mode of life 

  • Amphibians are the first vertebrates who made the transition from aquatic to the terrestrial mode of life.


Habit and habitat

  • Amphibians occur in freshwater and moist water.

  • There are no marine forms.

  • Some frogs live on trees. Example- Hyla (tree frog).


Temperature

  • It is (poikilothermal) and most forms hibernate in winter.

  • Some of them aestivate in the dry summer.


Body Form

  • Their body varies from broad to narrow, long to short and cylindrical.

  • It is divided into four parts which include head, neck, trunk, and tail

  • The neck is absent in some of the amphibians.


Appendages

  • There are two pairs of pentadactyl limbs, each with 4 - 5  pure digits.

  • In some amphibians limbs are absent (Apoda).

  • Hindlimbs are larger than four limbs present in frogs and toads for leaping.

  • These are near the same size as in salamander and newts.

  • Digits are without claws, nails or hoofs, and often have webs.


Skin

  • It is smooth and moist and rich in multicellular mucus and is poisonous glands.

  • It is highly vascular and is respiratory in most species

  • Scales are mostly absent ( except Apoda).


Endoskeleton 

  • It is largely bony.

  • Skull is flat and cacodylic i.e has two occipital condyles.

  • Notochord does not persist.

  • The first vertebra is specialized to provide some movement to the head.


Digestive System 

  • The mouth is large and armed with teeth in the upper or both jaws.

  • Teeth are acrodont.

  • Amphibians (frogs and toads) are the first vertebrates to have a true tongue.

  • A true tongue is a soft mucus coated and attached at the front end in frogs and toads.

  • The alimentary canal leads into the cloaca.


Respiratory System

Respiration takes place by

  • Lungs(Pulmonary respiration)

  • Living of buccopharyngeal cavity 

  • Skin ( Cutaneous respiration) 

  • Gills ( Branchial respiration) 


Circulatory System

  • The heart is 3- Chambered with two auricles and one ventricle.

  • This is an advancement over the 2-chambered fish heart.

  • The left and right auricles receive blood from the lungs and rest of the body respectively.

  • The ventricle pumps out mixed blood.

  • Sinus venous and truncus arteriosus are present.

  • The renal portal system is well developed.

  • RBC cells are biconvex, oval, and nucleated.


Cranial Nerves and Sense Organs

  • There are 10 pairs of cranial nerves.

  • There is no external ear.

  • In addition to the internal ear, a single auditory ossicle is present with the middle ear. 

  • Tympanum covers the middle ear.

  • Lateral line sense organs are present in larva and in aquatic forms.


Reproductive System

  • Gonoducts lead to colada.

  • Sexes are separate from sexual dimorphism.

  • Males lack a copulatory organ.


Fertilization and Development

  • Fertilization is mostly external (It is internal in salamander).

  • They are oviparous.

  • Life history often includes an aquatic larva(tadpole).

  • Amphibians have evolved from lung breathing, lobe-finned, bony fishes.

  • Their paired fins had a fleshy lobe that gives rise to limbs.

  • This ancestral is presently represented by living fossil Latimeria.

FAQ (Frequently Asked Questions)

1. Why should we take care of amphibians?

Amphibians play a very important in our environment or the ecosystem where they live. Amphibians are sensitive to pollution because their skins which are usually permeable in nature so, they easily absorb toxins. A diverse community of amphibians predicts that the particular area is healthy and helps by supporting the animal and the plant's life that herps want for food and cover. Some of the amphibians act as predators that maintain the number of prey in check, like snakes that eat rats and other rodents. Many species of mammals, fish, birds, and reptiles use other herps as their prey because they serve as a food source.

2. What can we do to help amphibians?

There are different types of ways to help and save the amphibians.


  • Encourage and support the work of the center for biological diversity by making a donation.

  • Prevent raccoons, crows, and predators from feeding our garbage.

  • Increase public awareness of the amphibian positively.

  • Get involved with local conservation projects and guide our neighbors to get involved in it too.

  • Avoid releasing environmental estrogens into the water. 

  • Reduce the use of pesticides and fertilizer which harms the amphibians most.