Shark belongs to class chondrichthyes, which means their endoskeleton is made up of cartilage. They are marine animals with sreamlined body and have seperate gill slit which are not covered or devoid of operculum. Shark is viviparous and have internal fertilization. They have modified electroreceptors present on their heads called ampullae of Lorenzini which can detect low electric potential. They have ventrally located mouth and skin is covered by minute placoid scales. Teeth in shark are backwardlly directed and they are modified placoid scales. They are Poikilothermous animals.