Explain the amphibian of vertebrata which belongs to the phylum chordata?

The amphibians are known as the two life organisms. They are the cold blooded animals who were first to evolve. The two life organism means they can live in water as well as on lands. They occur in warm countries. Their skin can be smooth or rough. They do not have scales but if the scales are present they occur beneath the skin. The fins are unpaired, while the limbs are paired and help in movement from one place to the other. The process of excretion and respiration occurs by a pair of kidneys which are mesonephric and with the use of gills along with the lungs respectively. The gills do occur in the larvae stage and in the adults they are replaced by lungs. They have no urinary bladder. They have well developed lateral line system. They occur mainly in the fresh water and they are not at all marine. They have the middle and internal ear. They have an outer membrane which covers the middle ear. The main excretory product in frog and toads is urea. The main excretory product in the larvae is ammonia. They have 20 cranial nerves. The skull has condyles which are 2 in number and have a vertebral column. The respiration is also supported by skin and buccopharyngeal cavity. Their heart is 3 chambered with a couple of auricles and a single ventricle. They do have SV and TA. They have well developed hepatic and renal portal system. They breed in water and the copulatory organs are absent in the male. They have a metamorphosis stage along with a fish like stage known as tadpole.