cephalon

Cephalon is a term used in arthropod anatomy to denote the head region or head shield. The word comes from the Greek kephale, meaning head. In trilobites, an extinct group of marine arthropods, the cephalon forms the anterior shield and bears several characteristic features. The central raised lobe is the glabella; the lateral fixed cheeks are the fixigenae, and the lateral free cheeks are the librigenae. Eyes, sometimes large and crescent-shaped, are often mounted on the cephalon. Facial sutures delineate the boundary between the cephalon and the rest of the body and influence the way the animal would molt. Cephalon shapes vary widely, from smooth to elaborately ornamented, and the cephalon is a primary unit used in trilobite taxonomy and functional interpretation of feeding and sensory capabilities.

In other arthropods, the term refers more generally to the head region. In crustaceans, for example, the cephalon may be distinct from the thorax or fused with it to form a cephalothorax, protected by a carapace. The cephalon also features prominently in anatomical descriptions and comparative studies of fossil and living species, reflecting its role in feeding, sensation, and overall morphology.