MAJOR ORDERS OF CLASS AMPHIBIA

Order (Apoda)Gymnophiona

🪱They are found in tropical and sub-tropical regions of Asia, Africa and America.

🪱Gymnophionans are primitive, burrowing forms.

🪱Limbs, limb bones and girdles absent.

🪱Eyes are rudimentary and nonfunctional and hence the name blind worms to these amphibians.

🪱Eyes are concealed by skin or covered by maxillary bones.

🪱Skin is transversely wrinkled or grooved. Minute dermal scales are embedded in the grooves.

🪱Sensory tentacle is found between the eye and nostril.

🪱Tail short or absent.

🪱Both jaws possess numerous teeth.

🪱Two pairs of aortic arches (systemic and pulmonary arches) are present. They are connected by a blood vessel called ductus Botalli.

🪱Male has protrusible copulatory organ.

🪱Skull is solid and compact with bony roof.

🪱Vertebrae are amphicoelous and pseudocentrous.

🪱Ribs long.

🪱Right lung is larger than the left.

🪱Larva has three pairs of external gills.

🪱Fertilization internal. In some forms, the females guard the eggs (parental care).

🪱Development is direct or indirect.

🪱Larval stage is present in oviparous forms.

🪱Larval stage absent in ovoviviparous forms.

Examples: lchthyophis, Uraeotyphlus

Order Anura (Salientia)

🐸Anura consists of frogs and toads.

🐸Anurans lack tail in adults.

🐸Two pairs of pentadactyl limbs are present . Hindlimbs and forelimbs are unequal. Hindlimbs are longer than the forelimbs and they are used for leaping and swimming.Toes are connected by web

🐸Head and trunk are fused.

🐸Neck is absent.

🐸Vertebral column has 5 to 9 vertebrae and a urostyle formed by the fusion of posterior vertebrae.

🐸Sternum is present.

🐸Ribs are rudimentary or absent.

🐸Teeth are present on the upper jaw only or absent.

🐸In adult, gills or gill openings are absent.

🐸Skin is naked, scaleless and glandular.

🐸Skull is dicondylic (two occipital condyles are present).

🐸Tympanum (eardrum) and middle ear cavity are present.

🐸Vocal cords are present.

🐸Fertilization and development are external.Development is indirect. Fish-like, gill breathing aquatic tadpole larva metamorphoses into adult.

Examples: Frog (Rana hexadactyla), Toad (Bufo)

Order Urodela (Caudata)

👽Most caudates occur in North America. Eastern Himalayan region contains one genus Tylotriton.

👽Urodela consists of newts and salamanders.

👽Body is lizard like. Distinct postanal tail is present. Tail fin, if present, has no fin rays.

👽Two pairs of weak and equal limbs are present.

👽Exoskeleton is absent.

👽Both jaws carry teeth.

👽Vocal cords are absent.

👽Vertebrae are opisthocoelous or amphicoelous.

👽Ribs are present. Sternum is poorly developed.

👽In male copulatory organ is present.

👽Tympanum is absent.

👽In terrestrial forms eye-lids are present. In aquatic forms lateral line sense organ is well developed.

👽Gills persist or lost in adult.

👽Fertilisation internal. 

👽Larva is aquatic and resembles the adult in external form.

Examles : Amblystoma (Ambystoma), Salamandra, Amphiuma, Triton, etc.