Phylum

Definition

A principal taxonomic rank in the Linnaean hierarchy, situated between kingdom and class, used to group organisms sharing a common body plan or fundamental structural organization. In zoology and entomology, phylum (plural: phyla) designates major lineages such as Arthropoda (jointed-legged invertebrates including insects, arachnids, and crustaceans), Mollusca, and Annelida. Botany traditionally uses 'division' as an equivalent term.

Etymology

From Greek phylon 'race, tribe, class', via New Latin phylum

Example

Insecta, Arachnida, and Crustacea are all classes within the phylum Arthropoda, united by chitinous exoskeletons, segmented bodies, and paired jointed appendages.

Synonyms

• division (botany)

Related Terms

• kingdom
• class
• Arthropoda
• Ecdysozoa
• taxonomic rank
• Linnaean hierarchy

Usage Notes

The plural 'phyla' is standard in scientific usage; 'phylums' is nonstandard. While kingdoms are few and broadly defined, phyla represent the fundamental architectural blueprints of animal life—there are roughly 35 animal phyla, with Arthropoda containing the vast majority of described species. The rank is absolute, not relative: a phylum is not 'more phylum' than another. Some molecular phylogenetic studies propose revising traditional phylum boundaries, but the rank remains stable in practice.