Muscle development in the marbled crayfish--insights from an emerging model organism (Crustacea, Malacostraca, Decapoda).

The development of the crustacean muscular system is still poorly understood. We present a structural analysis of muscle development in an emerging model organism, the marbled crayfish--a representative of the Cambaridae. The development and differentiation of muscle tissue and its relation to the mesoderm-forming cells are described using fluorescent and non-fluorescent imaging tools. We combined immunohistochemical staining for early isoforms of myosin heavy chain with phallotoxin staining of F-actin, which distinguishes early and more differentiated myocytes. We were thus able to identify single muscle precursor cells that serve as starting points for developing muscular units. Our investigations show a significant developmental advance in head appendage muscles and in the posterior end of the longitudinal trunk muscle strands compared to other forming muscle tissues. These findings are considered evolutionary relics of larval developmental features. Furthermore, we document the development of the muscular heart tissue from myogenic precursors and the formation and differentiation of visceral musculature.