Class: Chondrichthyes: marine fishes having cartilaginous endoskeleton. Five to seven pairs of gills. Gill-slits not covered by operculum. Male fishes have pelvic claspers. Example: Scoliodon, Chimera.
Class: Osteichthyes: Endoskeleton bony, skin having various types scales. Gill slits covered by operculum. Male fishes without claspers, Example: Labeo (Rohu), Protopterus (Lung fish), Hippocampus (Sea horse).
Superclass: Tetrapoda: Land vertebrates with two pairs of pentadactyl limbs; have cornified skin and lungs. Tetrapoda is divided into four classes;
Class: Amphibia: Adults are amphibious and respire by lungs. Breathe by gills, skin moist, glandular and with no external scales. Heart 3-chambered and cold blooded. Example: Rana (Frog), Bufo (Toad).
Class: Reptilia: terrestrial, dry skin and covered by ectodermal horny scales or bony plates. Heart incompletely 4-chambered and cold blooded. Example: Hemidactylus (lizard), snakes, turtles, Crocodiles.
Class: Aves: Body covered with feathers. Forelimbs modified into wings. No teeth in beak. Heart 4 chambered. Warm blooded. Example: Ostrich, Columba (Pigeon), crow, male tufted duck, white stork.
Class: Mammalia: body covered by hair. Skin glandular, Mammary glands present and in females, mammary glands secrete milk for suckling the young. Heart 4 chambered warm blooded. Example: Echidna (Spiny anteater), Macropus (Kangaroo), Humans, Whale, Elephant, tiger, cat, bat, etc.