Write eight salient features of the class - Amphibia.

Explanation

General characters of Amphibia :
1. They are the first tetrapods and lead a dual mode of life, i.e. on land and in freshwater.
2. Body is divided into distinct .head. and .trunk.. Tail may or may not be present.
3. Skin is soft, scale-less (except the members of Apoda), moist and glandular.
4. The body bears two pairs of equal or unequal pentadactyle limbs (caecilians are limbless).
5. Skull is dicondylic as in mammals. Vertebrae are mostly precoelous (centrum is concave at its anterior face only) in the anurans, amphicoelous in the caecilians and usually opisthocoelous (centrum is concave at its posterior face) in the urodeles. Sternum appeared for the first time in the amphibians.
6. Mouth is large, teeth are acrodont, homodont and polyphyodont.
7. Respiratory gaseous exchange is mostly cutaneous, pulmonary and buccopharyngeal respirations also occur. Branchial respiration is performed by larvae and some adult urodeles.
8. Heart is three-chambered with sinus venosus and conus arteriosus. Three pairs of aortic arches and well-developed protal systems are present, erythrocytes are nucleate.
9. Kidneys are mesonephric, ureotelic.
10. Meninges are the inner piamater and outer duramater, cranial nerves are 10 pairs.
11. Middle ear consists of a single ear ossicle, the columella auris which is the modified .hyomandibula. of the fishes. Tympanum, lacrimal and harderian glands appeared for the first time in the amphibians.
12. Sexes are separate and fertilization is mostly external. Development is mostly indirect.
E.g. Bufo (toad), Rana (frog), Hyla (tree frog), Salamandra (salamander), Ichthyophis (limbless amphibian), Rhacophorus (flying frog).