Explain how animals in Vertebrata are classified into further subgroups.

(A) Animals in Vertebrata are classified into five main classes:
$(i)$ Class Pisces: This class includes fish such as $Scoliodon$,tuna,rohu,shark,etc. These animals are aquatic. They possess adaptive features like a streamlined body,a tail for movement,and gills for respiration.
$(ii)$ Class Amphibia: This includes frogs,toads,and salamanders. They have a dual mode of life. In the larval stage,they respire through gills,while in the adult stage,respiration occurs through lungs or skin. They lay eggs in water.
$(iii)$ Class Reptilia: This includes reptiles like lizards,snakes,and turtles. They typically creep or crawl on land. Their body is covered with dry,cornified skin to prevent water loss,and they lay eggs on land.
$(iv)$ Class Aves: This includes all birds such as sparrows,pigeons,and crows. Most possess feathers. Their forelimbs are modified into wings for flight,while hind limbs are adapted for walking and clasping. They lay eggs.
$(v)$ Class Mammalia: This includes animals that possess milk-producing (mammary) glands to nourish their young. Some lay eggs,while others give birth to live young. Their skin features hair,sweat glands,and oil glands to regulate body temperature.