The animal kingdom is the taxonomic kingdom that comprises of all extinct and living animals. This is biggest kingdom with over one million species. Within the animal kingdom there are subcategories including division, class, order, family, genus, and species. Some characteristics the organisms in the animal kingdom have include being: multicellular, heterotrophy, reproducing sexually, and capable of moving some time in their life. Their cells are eukaryotic and lack cell walls. For respiration, most animals take in oxygen and release carbon dioxide through lungs, gills, skin, and diffusion. This fish is an example of an organism in the animal kingdom.