sternites

Sternites are the ventral sclerotized plates of arthropod body segments, found on the underside of most segments and operating opposite the dorsal tergites. Collectively they form the ventral part of the exoskeleton and serve as sites for muscle attachment and articulation with adjacent segments.

In insects, sternites are present on thoracic and abdominal segments. The thorax typically bears a prosternum (the ventral plate of the prothorax) and, on the mesothorax and metathorax, a mesosternum and metasternum; these may be fused or variably reduced in some lineages. Abdominal sternites appear on each segment and can be exposed or partially concealed by intersegmental membranes. The morphology of sternites—such as their shape, sutures, and degree of fusion—varies with development, sex, and evolutionary lineage, and they can influence the flexibility and movement of the thorax and abdomen.

In crustaceans and other arthropods, sternites similarly form ventral plates on body segments, though their exact structure and degree of calcification can differ among groups. Some segments may show reduced or modified sternites, particularly where extensive pleural or ventral structures dominate the segmental architecture.

Functionally, sternites provide protection for ventral organs, serve as attachment points for muscles (including those that operate legs and abdomen), and contribute to the segmentation pattern that underpins locomotion and respiration in certain taxa. Because their size, fusion, and patterning can be taxonomically informative, sternites are frequently described in comparative anatomy and systematics.