Vertebrata is the main category in the kingdom animalia. Vertebrates are are divided into 2 major categories. Agnatha and Gnathostomata. Agnatha represents those organisms in vertebrae without jaw. Inside the agnatha there is a single class called Cyclostomata. (Don’t get confused with Gnathostomata) . The features of this class are they are parasites in fishes with 6-15 pair of gill slits with closed circulation. Another division of Vertebrata is Gnathostomata ,or organisms with jaw . It is divided into superclass pisces and Tetrapoda. Pisces are fishes or they bear fins while tetrapoda bears limbs. Pisces is divided to Chondrichthyes and Osteichthyes . Tetrapoda can be divided into 4 classes named amphibia , reptilia, aves and mammals. Chondrichthyes are cold blooded organisms while all others are warm blooded organisms