Phylum and Kingdom

Phylum and Kingdom sit at the top of the animal taxonomic hierarchy, grouping ever-broader assemblages of classes. A phylum brings together classes that share distinctive common characteristics — the textbook's example is Phylum Chordata, which unites the classes Pisces (fishes), Amphibia (amphibians), Reptilia (reptiles), Aves (birds) and Mammalia (mammals). Although these five classes look extremely different from one another, they all share defining chordate features, specifically the presence of a notochord (or, in vertebrates, a vertebral column/backbone derived from it) and a dorsal, tubular nerve cord — features that justify grouping them together despite their enormous outward diversity. …