Regional distribution of muscle fiber types in the asymmetric claws of Californian snapping shrimp [Alpheus californiensis]

The properties of the opener and closer muscles in the asymmetric claws of Alpheus californiensis have been investigated using sarcomere length measurements and histochemical techniques. In the smaller pincer claw two types of muscle fibers are regionally distributed within the single closer muscle. A central band of fibers have short (2.5 μm) sarcomeres and high myofibrillar ATPase activity. Intermediate-type fibers have smaller diameters, sarcomeres 8.5 to 9 μm in length and low myofibrillar ATPase activity. The snapper closer muscle, by contrast, is composed of fibers with long (11-14 μm) sarcomeres and low myofibrillar ATPase activity. Opener muscle fibers in the pincer claw have shorter sarcomere lengths than their counterparts in the snapper claw.