Tergum — dorsal plate of an arthropod segment

Structure and terminology

Terga may be continuous or subdivided and commonly form sclerites — hardened exoskeletal plates — that are visible from above. In insects the dorsal plate of a thoracic segment is often called a notum (for example, pronotum on the prothorax), while abdominal dorsal plates are typically called tergites. Terga can be joined or fused (forming a syntergum) or reduced and membranous in some taxa.

Functions and variation

The dorsal plates provide protection, surfaces for attachment of muscles and, in certain insect groups, support for wings and wing musculature. Terga vary in sculpture, size, and ornamentation: they may bear spines, setae (bristles), glands, color patterns or keels used for display or defense. In crustaceans and some myriapods terga may be modified into a carapace or form part of a composite dorsal shield.

Importance in identification and study

Features of terga and tergites are important characters in taxonomy and identification. The number, shape, sculpture, sutures and relative sizes of tergites are commonly used in descriptive anatomy and identification keys across insects, crustaceans and other arthropods. Paleontologists and comparative anatomists also examine tergal structures to infer movement, lifestyle and phylogenetic relationships.

Related terms and distinctions

• Tergite — an individual dorsal sclerite within a tergum.
• Notum — the dorsal region of an insect thoracic segment.
• Sternum — the corresponding ventral plate of a segment.
• Syntergum — two or more terga fused into a single plate.

Understanding the tergum and its variants helps clarify external arthropod anatomy and supports comparative studies across diverse groups of invertebrates.