apodeme (ap'-o-deme). One of the ingrowths from the exoskeleton of many arthropods that provide points of muscle attachment, such as an invagination of the body wall of an arachnid, an inward deflection of a sclerite of a merostome, a downward projection from the dorsal interior of a thoracic segment of a trilobite, or an infold of the exoskeleton of a crustacean.