Metamérie

Metamérie, in biology commonly referred to in French as métamérisme, is the property of an animal’s body to be divided into a linear series of repeated units called metamères. This modular organization is found in a range of animal groups, most notably in annelids (such as earthworms and polychaetes), arthropods (insects, crustaceans, and arachnids), and, to varying extents, in chordates.

Structure and variation: Each metamer typically contains components of major organ systems, including parts of the circulatory and nervous systems and elements of the locomotor apparatus. In some groups, metamères are externally visible as segmented rings or blocks along the body; in others, segmentation is primarily internal, as seen in the somites of vertebrate embryos that contribute to the skeleton and associated musculature.

Development and genetics: Metamerism arises from developmental gene networks that pattern the anterior–posterior axis, including segmentation genes and Hox genes in many taxa. The degree of repetition can change during growth through processes such as segment addition, regional specialization, or tagmatization, leading to different functional units along the body.

Function and evolution: Segmentation can support modular growth, functional specialization of body regions, and redundancy of organ systems, conditions that can facilitate ecological diversification and evolutionary adaptability.

Terminology: In French scientific usage, métamérisme or métaméries refer to this phenomenon; in English, metamerism is the standard term. Metamérie thus represents the linguistic variant commonly used to describe a universal biological principle.

See also: segmentation, somite, metamere, metamerism in invertebrates.