Propleuron

Definition

The lateral sclerite of the prothorax in insects, forming the side wall of the foremost thoracic segment and typically bearing the pleural sulcus and the pleurocoxal articulation for the foreleg. The propleuron lies between the pronotum dorsally and the prosternum ventrally, and is usually smaller and less structurally complex than the mesopleuron and metapleuron of the middle and hind thoracic segments.

Etymology

Greek pro- (before, foremost) + pleuron (side, rib)

Example

In beetles (Coleoptera), the hypertrophied pronotum often extends downward to conceal much of the propleuron from dorsal view, whereas in grasshoppers (Orthoptera) the propleuron remains exposed and visible as a distinct lateral plate anterior to the larger mesopleuron.

Related Terms

• prothorax
• pronotum
• Prosternum
• mesopleuron
• metapleuron
• pleuron
• pleural sulcus
• episternum
• epimeron

Usage Notes

The propleuron is generally simpler in structure than the pleura of the pterothoracic segments (meso- and metathorax), lacking the elaborate internal apodemes and muscle attachments associated with wing bases. In some insect groups, the propleuron may be partially or fully fused to adjacent sclerites; in others, it remains clearly separated by sutures. The term is not used for arachnids, which lack a true thorax and pleural sclerites homologous to those of insects.