prosomal

Prosomal is an anatomical term used to describe structures related to the prosoma, the anterior region of certain arthropods, most notably arachnids. The word derives from Greek and is often contrasted with the opisthosoma, the rear body region.

In spiders, scorpions, harvestmen, and many mites, the prosoma corresponds to the cephalothorax—the fused head and thorax to which the legs and appendages attach. The prosoma bears the eyes and mouthparts (chelicerae and pedipalps) and is connected to the opisthosoma by a flexible waist in spiders, allowing body movements.

In other chelicerates such as horseshoe crabs (Xiphosura), the prosoma is the broad anterior shield or carapace, with the opisthosoma forming a segmented abdomen. The two regions are externally distinct, and the prosoma often houses major sensory and feeding structures.

In some mites, the boundary between prosoma and opisthosoma is less evident because the body is dorsoventrally flattened or the two regions are fused. In these cases, the term prosomal shield is used to describe a prominent dorsal plate at the front of the body.

Usage and scope: Prosomal is used primarily in anatomical descriptions rather than taxonomy. It is commonly paired with terms such as prosomal segments, prosomal shield, and prosomal appendages to specify features located on the anterior body region.

See also: cephalothorax, opisthosoma, arachnid anatomy, Xiphosura.