Suture

Definition

A line or seam along which adjacent sclerites (hardened cuticular plates) of the arthropod exoskeleton meet, articulate, or were formerly fused; externally visible as an inflection, groove, or impressed line marking the junction between body wall elements. In living specimens, sutures typically represent flexible cuticle allowing movement between plates; in fossils, they may indicate original boundaries of fused segments or tagmata. The term also applies to internal cuticular inflections where muscles attach.

Etymology

From Latin sutura, meaning 'a sewing' or 'seam', referring to the joined appearance of adjacent plates.

Example

The ecdysial suture (also called ecdysial cleavage line) on the head of a cicada nymph runs from the anterior margin of the compound eye to the base of the antenna; during molting, the old cuticle splits along this line to allow the adult to emerge.

Synonyms

• sutural line
• cleavage line (when ecdysial)

Related Terms

• Sclerite
• ecdysial line
• Eclosion
• tagma
• Cuticle
• arthrodial membrane
• Sulcus

Usage Notes

Distinguish from surgical sutures (stitches) or geological sutures (tectonic boundaries). In entomology, 'suture' often specifically denotes the elytral suture in beetles (Coleoptera), the straight midline where the two hardened forewings meet at rest; this is a highly visible diagnostic character. Not all apparent lines on the exoskeleton are true sutures—some are sulci (grooves) or sclerite boundaries without underlying flexibility. The adjectival form 'sutural' is common in morphological descriptions (e.g., 'sutural stria', 'sutural spine').