pleurons

Pleurons are the lateral plates or side sclerites of segmented arthropod body regions, especially evident on thoracic or trunk segments. The term is derived from the Greek pleura, meaning "side." In insects the pleuron forms the lateral wall of a thoracic segment and is typically subdivided by sutures into an anterior episternum and a posterior epimeron; these divisions provide attachment sites for muscles and articulations for legs and wings. In crustaceans and trilobites the pleura are the lateral extensions of each somite and may be developed into broad plates, narrow flanges, or spines.

Functionally, pleurons protect the lateral soft tissues, contribute to the rigidity of the exoskeleton, and serve as important loci for muscle attachment and limb articulation. In many crustaceans they help delimit branchial chambers or provide space for the base of appendages. Morphological variation in pleuron shape, size, and ornamentation is frequently used in taxonomy and inferences about ecology and locomotion, for example distinguishing burrowing from free-swimming forms.

The term can be confused with "pleon," which denotes the abdominal region in some crustaceans; pleuron refers specifically to lateral sclerites. Historical and comparative anatomy literature sometimes uses different pluralizations (pleura, pleurae, pleurons), but the concept consistently denotes lateral segmental structures across diverse arthropod groups.