Tagma (biology)

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This article is about biology; for the Byzantine military grouping, see tagma (military).

In invertebrate biology, a tagma (plural tagmata) is a specialized grouping of arthropodan segments, such as head, body, and tail.

The arthropodan body is divided into numerous segments, also called somites or metameres, that are primarily alike. These segments are grouped into specialized divisions called tagmata. The segments of a tagma may either be fused or moveable.

Tagma divisions vary among superclasses. For example, in trilobites the tagmata are the cephalon (head), thorax (body), and pygidium (tail). However, in hexapods, these same divisions are called head (head), thorax (body), and abdomen (tail).

The evolutionary process which creates tagmata by fusing and modifying segments is called tagmosis.

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