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How does an arthropod exoskeleton support muscle attachment?

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A pangolin walks through grass with a blue circle around it and the word endangered written in white across the image. — Integument The pangolin is the only mammal in the world covered in scales.

In arthropods, the exoskeleton provides a rigid framework that supports muscle attachment, enabling movement independent of hydrostatic pressure. This attachment is facilitated by several specialized structures and biological mechanisms:12

Apodemes: These are hollow, inward-extending rods or flanges derived from the cuticle. They function similarly to vertebrate bones by providing specific sites for muscle insertion, which allows for the leverage necessary to move skeletal segments.23
Tonofibrils: Muscle fibers or their connective-tissue supports are anchored to the cuticle via tonofibrils, which are located within the cytoplasm of the ectodermal cells that secrete the cuticle.1
Sclerites and Joints: The exoskeleton is composed of stiffened plates called sclerites, which are separated by flexible joints. Antagonistic muscle pairs span these joints, allowing for controlled movement of the limbs and body segments.14
Muscle Architecture: Because arthropod legs have limited space, many of their muscles are pennate—meaning short fibers attach diagonally to an apodeme. This arrangement allows the muscles to exert significant force despite the physical constraints of the exoskeleton.3