metasternum

Metasternum is the ventral plate of the metathorax in hexapods, particularly insects. The thorax consists of three segments—prothorax, mesothorax, and metathorax—each with dorsal and ventral sclerites. The metasternum is the sternite of the metathorax and forms part of the thoracic exoskeleton that underlies the hind-body region. It provides a major site for muscle attachments that move the hind legs and, in winged species, interacts with the bases of the hind wings and associated structures.

The size and shape of the metasternum vary among taxa. In some groups it is well developed, offering robust support for leg movement and thoracic mechanics; in others it is reduced or fused with adjacent sternites or abdominal plates as part of body-plan modifications. The metasternum is typically bordered by pleural sclerites and connected to neighboring sternites by sutures, with variations reflecting different developmental and functional adaptations.

In evolutionary terms, changes in the metasternum can accompany shifts in locomotion, wingness, and thoracic segmentation. It remains a key landmark in insect anatomy for identifying segmental boundaries and understanding hind-leg articulation.

Etymology: metasternum derives from meta- meaning “after” or “beyond” and sternum meaning “breastbone,” reflecting its position on the ventral side of the metathorax.

See also: sternum, sternite, thorax (insects), insect anatomy.