sclerotized

Sclerotized is a biological term used mainly in invertebrate anatomy to describe body parts that have hardened and become rigid through sclerotization. In arthropods, the exoskeleton and certain mouthparts are sclerotized, whereas other soft tissues may remain unsclerotized.

Biochemical process: Sclerotization strengthens the cuticle by forming stable covalent cross-links between cuticular proteins and chitin; this cross-linking is mediated by quinones produced by enzymatic oxidation of phenolic precursors, often via phenoloxidase. The process also involves tanning-like reactions and sometimes pigmentation that darkens the cuticle.

Anatomical aspects: The insect cuticle consists of epicuticle, exocuticle, and endocuticle. Sclerotization predominantly affects the exocuticle, leading to increased hardness and reduced permeability, while the endocuticle remains more flexible in many regions. The degree of sclerotization varies by species and body region; wings, mandibles, and dorsal plates are often highly sclerotized, while joint membranes are less so.

Function and significance: Sclerotization provides mechanical strength for muscle attachment, protection against abrasion, and barrier against desiccation. It also influences the mechanical properties of joints and the performance of feeding structures.

Desclerotization and development: After molting, new cuticle is initially soft and becomes progressively sclerotized; controlled desclerotization is not typical but softening can occur during ecdysis.

Taxonomic relevance: The pattern and extent of sclerotization are used in identifying species and in describing morphological characters.

Note: The term is most commonly used for arthropods; in plants or fungi the term sclerotized is not typically applied.