Abstract

The large claw muscle of many crustaceans undergoes an extensive atrophy induced by the moult that facilitates withdrawal of the claw muscle mass through the narrow basal limb joint at ecdysis. We investigated the histological characteristics of the claw closer muscle of the yabby, Cherax destructor, at different stages of the moult cycle. During intermoult the chela was completely filled with muscle fibres and the fibres were of a uniform appearance being polygonal in shape. The apodeme separating the dorsal and ventral parts of the muscle appeared as a continuous chitinous sheet. During premoult significant signs of atrophy were apparent: the diameter of the muscle fibres decreased, spaces devoid of muscle fibres were present and these spaces contained connective tissue, and there was evidence that the apodeme had undergone partial degeneration. During the postmoult period, the signs of atrophy were not as evident and by the following intermoult period no signs of atrophy in the claw muscle were observed. This study reports for the first time that the atrophy that occurs in the claw muscle is not uniform but rather the severity of the atrophy increased in the claw along a proximo-distal axis, with the distal portions of the claw of one individual losing all fibres.

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