Animals are classified into different phyla based on fundamental body plans and structural features. Key characteristics considered in this classification include the type of symmetry (bilateral or radial), the presence of a nervous system, body segmentation, and whether they possess a coelom (body cavity). For example, phyla such as Chordata includes animals with a notochord, while Arthropoda encompasses those with jointed limbs and exoskeletons. The classification reflects evolutionary relationships and helps in understanding the diversity of life on Earth.