Introduction to Amphibia
In the animal kingdom, class Amphibia refers to all amphibians- which are animals capable of surviving both on land and in water. These are vertebrates that are usually not very large in size. This term is derived from the Greek term ‘amphibious’ which essentially implies ‘double life’. This points to the fact that amphibians can live both in aquatic and terrestrial environments. However, within amphibians, it is possible to find animals that live completely on land or completely in water.
Amphibians are a crucial link that determines all life forms that began from the oceans. Around 8000 species of amphibians have been documented to date. Their species came into existence back in the Middle Mississippian Epoch. While this has not been completely proven correct, it is believed by scientists that what we today know as amphibians were in fact the first animals that made the shift from sea to land.
Amphibians are found everywhere in the world except in the antarctic region. They exist in the Arctic regions as well, and also in arid conditions. They are very useful in the production of crops since most varieties of amphibians usually attack and feed on insects that damage crops.
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
Cryptobranchoidea
Most primitive, permanently aquatic
Adult without eyelid
External fertilization occurs
Example- Cryptobranchus
Ambystomoidea
Living on land
Adult with eyelid
Internal fertilization
Example- Ambystoma
Salamandridae
Opisthocoelous Vertebrates are present
Teeth are found on the roof palate
Internal fertilization.
Example- Salamander
Provider
Living as aquatic animals
Without eyelids and lungs
Cartilaginous skull
Example - Proteus
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
Characteristics of Class Amphibia
General Characters
Amphibians are those animals that can live on 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).
TemperatureIt is (poikilothermic) and most forms hibernate in winter.
Some of them are active 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 salamanders and newts.
Digits are without claws, nails or hoofs, and often have webs.
SkinIt is smooth and moist and rich in multicellular mucus and has poisonous glands.
It is highly vascular and is respiratory in most speciesScales 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 venosus 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 gave rise to limbs.
This ancestral species is presently represented by the living fossil Latimeria.
FAQs on Amphibia
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.
3. How do amphibians breathe?
Amphibians are capable of living both on land and in water, and therefore, they have a peculiar breathing apparatus. It is not possible for them to breathe through their noses like mammals do since this would transfer water into their lungs. Most amphibians are found to be breathing through their skin. Their skin is primarily the most important part of their body because it aids them in respiration. It is important for them to have wet or at least moist skin at all times so that they can absorb moisture. When amphibians are outside of water, they secrete a mucus-like substance so that their skin remains moist.
4. How do amphibians reproduce?
Amphibians cannot reproduce asexually. They need sexual reproduction. This can be either external or internal fertilization. An important point to note is that amphibians do not produce eggs, and they usually always mate while they are in the water. They go through the entire mating process like most other animals, using pheromones to attract potential mates. Once they finish mating, the amphibian larvae are required to undergo metamorphosis before they can change into their adult stages. This step is important because while mammals give birth and other vertebrates lay eggs, amphibians do neither. Their eggs do not have an amniotic sac and thus they produce dozens of larvae into the water.
