In biological classification, a "phyla" (singular: phylum) is a major taxonomic rank that groups together organisms sharing a common body plan and structural features. Phyla are one of the primary categories used in the hierarchical system of classification, which includes domains, kingdoms, and species. For example, the Chordata phylum includes all animals with a notochord, such as mammals, birds, and fish. Each phylum can be further divided into classes, orders, families, genera, and species, allowing scientists to categorize the vast diversity of life on Earth. Other well-known phyla include Arthropoda, which encompasses insects and crustaceans, and Mollusca, which includes snails and octopuses. Understanding phyla helps in studying evolutionary relationships among different organisms.