Fig. 1. Diagram of cutter claw with lateral portion of exoskeleton removed to reveal the arrangement of the closer muscle. The central region of the muscle is composed of large fibers that are the fast phenotype. The ventral and distal regions of the closer are slow, with the ventral region composed of S₁ fibers and the distal region composed of S₂ fibers. Previous work by Lang et al. (1980) demonstrated that these regions are controlled by phasic (central), tonic (distal) or both (ventral) motor neurons. The same study showed that the distal region of both claws possessed highly oxidative fibers. The basic anatomy of the crusher claw is similar to that of the cutter but is composed entirely of S₁ fibers.