Prothorax

The prothorax is the first of the three thoracic segments in insects (hexapods) and forms the anterior part of the thorax between the head and the mesothorax. It bears the first pair of legs and provides attachment and muscular support for their movement. The dorsal plate of the prothorax is called the pronotum, a key exterior feature used in identification in many groups.

Anatomy and structure: The prothorax consists of the pronotum (dorsal), the prosternum (ventral), and lateral pleural regions. In most adult insects the forelegs arise from the prothorax, while wings, if present, attach to the mesothorax and metathorax rather than the prothorax. The relative size and shape of the pronotum can vary greatly among species, ranging from a compact shield to a more elongated, shield-like plate.

Function and variation: The prothorax provides protection and muscular leverage for the forelegs, which are essential for locomotion, grasping, or prey capture in many species. In some insects, especially those with a long neck-like appearance such as mantises, the prothorax is greatly elongated to allow a greater range of head movement. In many winged groups, the prothorax is not the wing-bearing thoracic segment; wing pads may appear on the prothorax in immature stages of some species, but wings typically develop on the mesothorax and metathorax in adulthood.

Etymology and scope: The term prothorax refers specifically to the first thoracic segment in insects. While widely used in entomology, the concept may be extended in some discussions of other arthropods, where comparable anterior thoracic segments exist.

In summary, the prothorax is the anterior thoracic segment that hosts the first pair of legs and includes the pronotum, playing a central role in locomotion and, in some taxa, neck mobility.