Class Amphibia

Class Amphibia (Greek amphi = both, bios = life) includes animals such as Rana (frog), Bufo (toad), Salamandra (salamander), Ichthyophis (a limbless amphibian) and Hyla (tree frog).

As the name suggests, amphibians can live both on land and in fresh water (though not in the sea). They are poikilothermic. The body is differentiated into a head and trunk; a distinct neck and tail are usually absent in most adults, with a few exceptions. Two pairs of limbs, arising from the pectoral and pelvic girdles, assist in locomotion. The skin is moist and glandular, containing mucous glands, and there is no exoskeleton. Eyelids are present, and the ear is represented externally by a tympanum (ear drum).

Excretory products, digestive waste and gametes are all released through a single common chamber, the cloaca. The circulatory system is closed, and the heart is three-chambered and ventrally positioned. Red blood cells are biconvex and nucleated. Respiration takes place through the skin, lungs and the lining of the mouth and throat (buccopharynx). The nervous system is well developed. …