Amphibia (Class) – Characteristics, Classification, Examples

Amphibians are cold-blooded tetrapod vertebrae belong to animal kingdom.

General Characteristics of Amphibia

  1. The representative of Class- Amphibia well both on land and in water, i.e., are amphibious.
  2. They are cold-blooded (poikilothermal) vertebrates.
  3. Skin is smooth, scale-less, rich in glands that keep it moist.
  4. Autostylic jaw suspension.
  5. Skull articulates with the atlas by two occipital condyles.
  6. Auditory columellar apparatus fitting into fenestra ovalis.
  7. Respiration in adult using lungs, skin and buccal epithelium. External gill may be present in some cases.
  8. Limbs are tetrapodous and pentadactyle type. Median fin when present, is without fin rays.
  9. Red blood corpuscles are oval, nucleated and biconvex.
  10. Heart three-chambered with two auricles and one ventricle, sinus is venous and truncus is present.
  11. Aortic arches are symmetrical; one pair of systemic arches present.
  12. The kidney is mesonephric with a nephrostome.
  13. Ten pairs of cranial nerves are present.
  14. Lateral sense organs are present in larval stages.
  15. Eggs laid in water and are enclosed in a gelatinous covering.
  16. The larva is a tadpole that metamorphoses into an adult. Amnion is absent.
  17. Examples of Amphibians are: Toad (Bufo), Frog (Rana), Salamander (Ambystoma)

Classification of Class Amphibia

Subclass 1: Lissamphibia

  • Modern living amphibia.
  • Without dermal body skeleton.

Order 1: Apoda (Gymnophiona)

  1. Primitive burrowing forms.
  2. Body elongated, eel like.
  3. Limbs and tails are absent.
  4. Skin with numerous wrinkles or grooves.
  5. Minute dermal scales lie embedded in skin.
  6. Copulatory organs are present in male.
  7. Example: Ichthyophis, Uroaeotyphulus

Order 2: Urodela or Caudata

  1. The body is divisible into the head, neck, trunk and tail.
  2. Two pairs of limbs, usually of equal size, but weakly developed.
  3. Tympanum absent.
  4. Larvae, aquatic, show Neoteny or Paedogenesis.
  5. They may retain external gills and median fins.
  6. Examples: Salamandra, Ambystoma, Tritus (newt), Proteus, Necturus (mud puppy), Siren (mud eel).

Order 3: Salientiea or Anura

  1. Body divisible into head and trunk. Tail is absent.
  2. Forelimbs are shorter than compared to hind limbs. Hind limbs are adapted for leaping and swimming.
  3. Tympanum present.
  4. Adult without gills.
  5. Teeth are absent in lower jaw.
  6. Examples: Rana, Hyla, Bufo etc.

Subclass 2: Stegocephalia

  1. Skull roof solid.
  2. These are extinct now.

Examples of Class Amphibia

1. Ichthyophis

Classification of Ichthyophis

PhylumChordata
SubphylumVertebrata (Craniata)
DivisionGnathostomata
ClassAmphibia
OrderApoda or Gymnophiana
GenusIchthyophis

Distribution

  • It is found in India (Karnataka), Sri Lanka, Malaysia, Islands, Myanmar, Malabar, Borneo and Java.

Habits and Habitat

  • This is limbless amphibians usually lives in moist soil and leads a burrowing life.
  • It feeds on invertebrates.

Characteristics Features of Ichthyophis

  1. It is commonly known as Caecilia.
  2. It is an elongated and eel-like animal.
  3. It measures up to 30 cm. in length.
  4. The color of the body is dark brown or bluish-black with yellow bands along the sides.
  5. The skin has numerous transverse grooves.
  6. Minute scales are embedded in the grooves of skin.
  7. Limbs and girdles are absent.
  8. The tail is short or vestigial.
  9. Eyes small, devoid of lids, buried deep in the head.
  10. A protrusible tentacle is present between the eyes and nostrils. It is a sensory organ.
  11. The tympanic membrane is absent.
  12. Sexes are separate, the male has a copulatory organ provided with hooks.
  13. Female coils around the eggs.
  14. Larva has three pairs of external gills.
Ichthyophis (Male)
Ichthyophis (Male)
Ichthyophis (Female)
Ichthyophis (Female)

2. Salamandra

Classification of Salamandra

PhylumChordata
SubphylumVertebrata (Craniata)
DivisionGnathostomata
ClassAmphibia
OrderUrodela
GenusSalamandra

Distribution

  • It is found in Europe, Eastern Asia and North America.

Habits and Habitat

  • Carnivorous, terrestrial, lives under stones, logs, barks and leaves of rotten trees.

Characteristics Features of Salamandra

  1. It is commonly known as European Fire salamander.
  2. Body is lizard like in appearance. The color is black with yellow spots.
  3. Limbs are well-developed and strong.
  4. Tail is cylindrical.
  5. Gills are absent in the adult.
  6. Eyelids are movable.
  7. Tympanic membrane or middle ear is absent.
  8. Parotid glands are present behind the head.
  9. Teeth are present on both the jaws.
  10. Female is longer than male.
  11. When roughly handled, it ejects poisonous milky fluid which causes burning pain.
Salamandra Labelled Diagram
Salamandra Labelled Diagram

3. Axolotl Larva

Classification of Axolotl Larva

PhylumChordata
SubphylumVertebrata (Craniata)
DivisionGnathostomata
ClassAmphibia
OrderUrotela
GenusAxolotl larva

Distribution

  • It is found in the lakes near Maxico city and also occurs from New York to California.

Characteristics Features of Axolotl Larva

  • The axolotl is the larva of Ambyostoma tigrinium.
  • Axolotl means servant of water or slave of water.
  • It never leaves the pond where it is living.
  • It shows the larval characters such as three pairs of external gills and a tail fin.
  • The young ones, in deficiency of iodine in water, become sexually mature and start reproducing. This phenomenon is called neoteny or paedogenesis.
  • Larva postpones the metamorphosis due to the abundance of food and oxygen in the water.
  • Metamorphosis can be induced by injecting the thyroid extract.
  • Axolotl is found in the ponds of Maxico.
Axolotl Larva
Axolotl Larva

4. Hyla (Tree Frog)

Classification of Hyla

PhylumChordata
SubphylumVertebrata (Craniata)
DivisionGnathostomata
ClassAmphibia
OrderAnura
GenusHyla

Distribution

  • It is commonly found in India, United States, China, Africa and Canada.

Habits and Habitat

  • It is arboreal in habit, living on trees.
  • Carnivorous, feeds on insects and worms.

Characteristics Features of Hyla

  1. Hyla is commonly called a Tree frog.
  2. It lives on the branches of the tree and rocks.
  3. The skin is smooth on the dorsal surface but bears papillae on the ventral surface.
  4. The head and trunk are fused.
  5. Eyes, nostrils and tympanum are well developed.
  6. Fingers and toes have adhesive discs or pads for sticking on the smooth surface used for climbing the tree.
  7. The web is poorly developed.
  8. Teeth present on upper jaws only and are absent on the lower jaw.
  9. Vocal sacs well developed for amplifying the sound.
  10. Exhibits mimicry, i.e., changes body color according to the environment.
  11. Female lays eggs in water fertilization us external.
  12. Development through tadpole larva.
Hyla labelled Diagram
Hyla labelled Diagram

5. Alytes

Classification of Alytes

PhylumChordata
SubphylumVertebrata (Craniata)
DivisionGnathostomata
ClassAmphibia
OrderAnura
GenusAlytes

Distribution

  • It is found in European countries, especially in France and Italy.

Habits and Habitat

  • It is an amphibious toad.

Characteristics Features of Alytes

  1. Alytes is commonly known as Midwife toad.
  2. The body is divisible into the head and trunk as the neck is absent. The body measures 2-3 inches in length.
  3. The body surface is dry, warty and bears papillae dorsally and ventrally.
  4. Eyelids are movable, and the tympanum is large.
  5. Vocal sacs are absent, and vertebrae are opisthocoelous.
  6. Forelimbs with four fingers and hind limbs with five toes.
  7. Male Alytes shows parental care by carrying bunches of eggs between its hind limbs. Male message the cloaca of the female with its forelimbs and the female expels the eggs in bunches.
  8. The male fertilizes the eggs externally and attaches the fertilized eggs to its hind limbs till tadpoles hatch and enter the water.
Alytes Labelled Diagram
Alytes Labelled Diagram

6. Bufo

Classification of Bufo

PhylumChordata
SubphylumVertebrata (Craniata)
DivisionGnathostomata
ClassAmphibia
OrderAnura
GenusBufo
Speciesmelanostictus

Distribution

  • It occurs in all the continents of the world except Australia.

Habits and Habitat

  • Bufo melanostictus is the common Indian toad, found in dry places, hidden under stones, dry fallen leaves and grasses.
  • Nocturnal and carnivorous, feeds upon worms and insects.

Characteristics Features of Bufo

  1. Bufo is commonly called True Toad.
  2. The body is divisible into the head and trunk.
  3. Skin is rough, dry and warty on the dorsal surface of the body.
  4. Eyes are large and nostrils are very small.
  5. The tympanum is very well-developed. Teeth are entirely absent.
  6. A pair of parotid glands are present behind the tympanum. These glands secrete a poisonous fluid that causes irritation when touched by man.
  7. Forelimbs bear three toes and a thumb pad.
  8. Hind limbs have three toes with the greatly reduced web.
  9. Eggs are laid in water in strings.
Bufo labelled diagram
Bufo labelled diagram

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