GENERAL CHARACTERISTICS OF CLASS AMPHIBIA.

 🐸Amphibians flourished during the Carboniferous period.

🐸They  live partly in water and partly on land, and hencethe name Amphibia (Greek: amphi - double, dual; bios - life) to the class.

🐸Most of the amphibians are now extinct.

🐸Cold blooded or poikilothermic vertebrates. Breed and develop in freshwater.Adult is terrestrial or partly aquatic.

🐸Skin moist and glandular.

🐸Exoskeleton absent. In some forms (apoda), concealed dermal scales are present.

🐸Two pairs of pentadactyl limbs are present. Digits are clawless. In someamphibians (apoda) limbs are absent.

🐸Skull dicondylic. i.e. two occipital condyles are present.

🐸Vertebrae are procoelous, amphicoelous or opisthocoelous.

🐸Respiratory organs in terrestrial adults are skin, lungs and buccal lining. Inaquatic larvae, gills are the respiratory organs.

🐸Heart is three-chambered.

The chambers are two atria and one ventricle.

🐸There are three pairs of aortic arches, namely, carotid, systemic and pulmocutaneous.

🐸Nostrils open into the buccal cavity.

🐸External ear is absent. Middle ear has tympanum (ear drum), eusta chian tube and columella auris (modified hyomandibular).

🐸Kidney is mesonephric. Urinary bladder is large.

🐸Amphibians are ureotelic(urea is excreted).

🐸Mouth is large. Upper jaw or both jaws bear homodont teeth. Tongue protrusible.

🐸Eggs are laid in fresh water or moist places. Eggs are covered with gelatinous material.

,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)