The major characteristics used to classify animals in vertebrata are :
    (i)    The kind of exoskeleton or endoskeleton.
    (ii)    The kind of respiratory organs.
    (iii)    The method of reproduction and giving birth to young ones.
    On the basis of above mentioned characters the vertebrata is divided into following classes :
    (a)    Exoskeleton of scales; Endoskeleton of cartilage or bones ; Breathing through gills …. PISCES.
    (b)    Breathing through gills only in larva ; Skin slimy …..AMPHIBIA.
    (c)    Exoskeleton of scales ; Laying eggs outside the water ….. REPTILIA.
    (d)    Exoskeleton of feather ; Lay eggs ; Flight possible ….. . …… AVES (Birds).
    (e)    Exoskeleton of hairs ; External ears ; Give birth to young ones ….. MAMMALIA.