Phyla

Phylum, plural phyla, is a major taxonomic rank used in the classification of living organisms. In most systems it lies below kingdom and above class, grouping together organisms that share a basic body plan and developmental strategy. In zoology, phyla are often distinguished by fundamental features such as symmetry (radial versus bilateral), body cavity type, tissue organization, segmentation, and embryology. In botany and mycology, the term is also used, though the equivalent rank is sometimes called division in some classification schemes.

Examples of animal phyla include Chordata (which contains vertebrates and their relatives), Arthropoda (insects, arachnids, crustaceans, and related groups), Mollusca (snails, clams, octopuses), Annelida (segmented worms), Nematoda (roundworms), Echinodermata (starfish and relatives), Cnidaria (jellyfishes, corals), and Platyhelminthes (flatworms). Porifera (sponges) is another early-diverging phylum. Phyla generally reflect major differences in organization that persist through evolution, making them useful for grouping biodiversity.

With the advent of molecular phylogenetics, the boundaries and relationships among phyla have been reconsidered. Some groups previously treated as separate phyla have been redefined or reassessed, and new phyla have been proposed or recognized as representing deep evolutionary splits. The concept of phylum remains a central, though sometimes debated, element of high-level biological classification.

In other kingdoms, phyla are also used in some classification schemes; in plants the term is often parallel to division (for example, Bryophyta, Magnoliophyta), and in fungi phyla such as Ascomycota and Basidiomycota are employed.