metameria

Metameria, or metamerism, is the pattern in which a body is organized into a series of repeating units called metameres or somites. The term is used most in biology to describe animal segmentation, but a parallel concept exists in botany, where shoots are viewed as a sequence of repeated phytomeres. In some languages, metameria is also used to refer to the color-m matching phenomenon known as metamerism in color science, though the latter is a distinct concept.

In animals, metamerism is most evident in groups such as annelids and arthropods, where the body is divided into serially arranged segments that may be similar in structure and function. Each metamer typically contains a repeating set of organs or organ systems, such as musculature, nerves, and circulatory components. In arthropods, segmentation is often accompanied by tagmosis, the grouping of metameres into specialized body regions like the head, thorax, and abdomen. In vertebrates, segmentation appears as somites along the developing embryo, contributing to the axial skeleton, musculature, and the lining of body cavities.

Embryologically, metamerism arises through different developmental mechanisms across lineages. In vertebrates, somite formation is driven by a segmentation clock in the paraxial mesoderm, producing a metameric pattern along the axis. In invertebrates, segmentation can involve iterative genetic and cellular processes that add segments sequentially.

In plants, metamerism describes modular growth in which stems are composed of repeated phytomeres, each including a leaf, a node, an internode, and an axillary bud. This modular organization underpins branching patterns and growth strategies.

Overall, metameria emphasizes modularity and repetition in body plans, while variations in segmentation reflect evolutionary diversification and functional specialization.