Sclerite

Definition

A hardened, plate-like section of arthropod integument, typically composed of sclerotin or calcified cuticle, that forms the structural units of the exoskeleton. Sclerites are joined by flexible, unsclerotized membranes (arthrodial membranes) that permit movement, and may bear muscles internally. In insects, sclerites are named by position: tergites (dorsal), sternites (ventral), and pleurites (lateral). The term also applies to the calcareous or siliceous spicules of certain sponges, cnidarians, and other soft-bodied invertebrates.

Etymology

From Greek skleros, hard

Example

The pronotum of a grasshopper is a single large sclerite covering the thoracic tergum; in beetles, the elytra are modified sclerites that protect the folded hindwings and abdominal tergites beneath.

Related Terms

• Sclerotin
• tergite
• sternite
• pleurite
• Exoskeleton
• Cuticle
• arthrodial membrane
• scleritome
• Tergum
• sternum

Usage Notes

Distinguished from 'sclerotin' (the hardened protein itself) and from general terms like 'plate' or 'segment.' In entomology, sclerite is preferred over 'plate' when emphasizing the hardened, articulated nature of the structure. The term is rarely applied to vertebrate structures; 'ossicle' or 'bone' are used instead. Sclerites may be further divided into smaller sclerites (e.g., antecosta, acrotergite) or fused into composite structures (e.g., the scutoscutellar shield in some Hemiptera).