Class : Amphibia

The members of Class Amphibia (Gr., Amphi : dual, bios, life) can live in aquatic as well as terrestrial habitats.

Examples:

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Bufo (Toad) Rana (Frog) Hyla (Tree frog)
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Salamandra (Salamander) Ichthyophis

(Limbless amphibia)

Body characteristics:

  • Body is divisible into head and trunk (tail is present in some of them). But neck is absent.
  • Trunk bears two pairs of limbs. Digits are without claws.
  • The amphibian skin is smooth and moist (without scales) due to the presence of mucous glands.
  • The eyes are provided with movable eyelids and a nictating membrane (third eyelid). The nictating membrane is a water-proof covering used when the animal is in water.

Evolution of An Amphibian

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  • A tympanum represents the ear.
  • Alimentary canal, urinary and reproductive tracts open into a common chamber called cloaca which opens to the exterior.
  • Respiration is by gills, lungs and through skin.
  • The heart is threechambered (two auricles and one ventricle). Hence, there is mixing up of oxygenated and deoxygenated blood inside the heart.

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Physiology: These are cold-blooded animals (poikilotherms).

Reproduction: Sexes are separate. Fertilisation is external (mostly in the water). They are oviparous and development is indirect. Larval stage has a tail, and is mostly aquatic.

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