subphylum

A subphylum is a taxonomic rank used in biological classification to group together major lineages within a phylum that share distinctive features. It sits below the phylum level and above ranks such as infraphylum or superclass, depending on the taxonomy employed.

The use of subphylum varies by phylum; some contain multiple subphyla, while others do not use the rank at all. Subphyla are common in zoological classifications and are sometimes replaced by different terminological schemes in cladistic contexts. They help reflect evolutionary relationships and developmental patterns among large, related groups.

Examples illustrate its application. In the phylum Chordata, typical subphyla include Cephalochordata (lancelets), Urochordata (tunicates), and Vertebrata (craniates, including fishes, amphibians, reptiles, birds, and mammals; Vertebrata is sometimes treated as Craniata in certain schemes). In Arthropoda, common subphyla include Chelicerata (spiders, scorpions, horseshoe crabs), Myriapoda (centipedes and millipedes), Crustacea (crabs, lobsters, shrimp, barnacles), and Hexapoda (insects and relatives). The extinct Trilobitomorpha is sometimes listed as a subphylum in older classifications.

Etymology-wise, the term derives from Latin sub- meaning “under” and phylum, reflecting its role as a subdivision of a phylum. The subphylum concept remains a practical, though not universal, tool for organizing animal diversity and communicating evolutionary relationships.