Ultrastructural characterization of superficial and deep flexor muscles in the crayfish thorax

Abstract

Transmission electon microscopy revealed that all of the superficial flexor muscle fibers in the crayfish thorax possess sarcomeres 8–10 μm in length, 12 thin myofilaments around each thick myofilament, no H zone, and irregular Z lines. This characterizes them as tonic. All of the deep flexor fibers possess sarcomeres 2–4 μm in length, six myofilaments around each thick myofilament, a distinct H zone, and Z lines that are perpendicular to the longitudinal axis of the fiber. This characterizes them as phasic. Differences in the distribution of mitochondria and glycogen granules and in the organization of synaptic regions also are noted.