Phylum (Plural: Phyla)

In determining these phyla, each of all the different basic body types has been considered. For instance, arthropods (jointed legs) are one separate phylum, and all the species in it have a similar body plan. The phylum known as Chordata contains all those species with a central nervous system. All the animals familiar to us, such as fish, birds, reptiles and mammals represent a subdivision-vertebrates-of the phylum Chordata.

Among the different animal phyla there are very different categories, such as Mollusca, which include soft-bodied creatures such as octopus, and the phylum Nematode, which includes roundworms. The categories beneath phyla have basically similar body plans, but phyla are altogether different from one another.