The animals are classified into 3 types depending on the type of nitrogenous waste material excreted by them.
They are:
1. Ammonotelic animals
2. Ureotelic animals
3. Uricotelic animals.
(1) Ammonoteiic animals: are the animals which predominantly excrete their nitrogenous waste material in the form of ammonia.
Examples: Crustaceans, Polychaete annelids, Octopus, Sepia, tadpoles of Amphibians and some teleosts fishes (bony fishes)
(2) Ureotelic animals : are the animals which predominantly excrete their nitrogenous waste material in the form of Urea.
Examples: Eiasmobranchs, Amphibians and Mammals.
(3) Uricotelic animals: are the animals which predominantly excrete their nitrogenous waste material in the form of uric acid Examples: Reptiles and Birds.