Class Amphibia includes animals that typically have a dual life cycle, with aquatic larval and terrestrial adult stages. They have moist, permeable skin that facilitates gas exchange, and their reproduction generally involves laying eggs in water. Amphibians breathe through gills during their larval stage and through lungs and skin as adults.
General Characters of Class Amphibia:
1) Habitat: They can live on land as well as in water.
2) Body Temperature: They are cold blooded (Poikilothermic) vertebrates.
3) Body: Body is divided into head and trunk. Tail present in some amphibians.
4) Heart: Heart is three chambered.
5) Respiration: Respiration through lungs (on land), and gills & skin (in water).
6) Limbs: Fore limbs are with four and hind limbs are with five clawless digit.
7) Skin: Skin naked, highly glandular, moist skin present.
8) Cranial Nerve: Ten pairs of Cranial nerves present.
9) Gut: Gut ends into a cloaca.
10) Fertilization: Fertilization generally external
11) Developement: Development is indirect through tadpole larva (aquatic).
12) Eye & Ear: The eyes have eyelids and tympanum represents the ear.
13) Condylyes: Skull is dicondylic i.e. with two occipital condyles.
14) Kidney: Kidneys are mesonephric type.
Examples: Bufo sp. (Toad); Rana sp. (Frog); Salamandra sp., etc.
Classification of Amphibians
Classification of Class Amphibia based on Duellman and Trueb (1986)
- Order Anura or Salientia
- Order Apoda or Caecilia
- Order Urodela or Caudata
1. Order Anura (An= without; oura = tail) or Salientia :
1) Body: These animals are short, four-legged and without tail.
2) Tail: The tail is present in Tadpole larval stage only.
3) Eyelids and Tympanum: They possess well developed eyelids and tympanum.
4) Fertilization: Fertilization is external.
5)Limbs: The posterior limbs are longer than the anterior limbs.
6) Head: The head and trunk are fused together.
Example: Rana tigrina (Frog); Hyla sp.; Rhacophorus sp., etc.
2. Order Apoda (without legs) or Gymnophiona or Caecilia :
1) Habitat: They are limbless burrowing organisms with scales.
2) Eye: They are also known as “Blind worms” because their eyes are covered by skin or maxillary bone.
3) Tongue: Tongue is fused with the floor of the mouth cavity.
4) Venom Gland: They possess venom gland.
5) Scales: Small, granular dermal scales are embedded in the body.
6) Tympanum: Both tympanum and tympanic cavity are absent.
Example: Ichthyophis sp.; Uroaeotyphlus sp. etc.
3. Order Urodela (oura-tail; delos = visible) or Caudata :
1) Body: These animals are lizard like appearance with two pairs of weak limbs and well developed tail.
2) Lateral Line: In aquatic forms a lateral line system is present.
3) Fertilization: Fertilisation is generally internal.
4) Kidney: Kidney is opisthonephric type.
5) Eyes: Small eyes are without lids. In cave dwellers, eyes are lost.
6) Gills: They possess hidden gills.
Example: Necturus sp.; Salamandra sp. (Salamander); etc.
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