Articulata

Articulata is a historical term used in the classification of Metazoa to describe a proposed clade of segmented animals with jointed appendages, primarily arthropods and annelids. The name derives from Latin articulatus, meaning “jointed.” The concept emerged in the 19th century as part of efforts to organize animals into major lineages, contrasting purportedly more primitive, radiate forms with bilaterian groups.

Proponents argued that segmentation and articulated limbs indicated a common ancestry among these groups, reflecting a shared developmental pattern. Critics, however, noted that such features could be convergent and that morphology alone might not reveal true evolutionary relationships.

In modern biology, Articulata is no longer regarded as a valid clade. Molecular phylogenetics and developmental studies place arthropods within Ecdysozoa and annelids within Lophotrochozoa, two distinct protostome lineages. This evidence undermines the unity of a single Articulata for segmented, jointed animals, and the term is now considered of historical interest rather than a component of current classifications.

See also: Radiata, Protostomia, Ecdysozoa, Lophotrochozoa.