Development of the muscle system and contractile activity in the mussel Mytilus trossulus (Mollusca, Bivalvia)

The development of contractile apparatus was subjected to comparative analysis during ontogenesis of the mussel Mytilus trossulus. Indirect immunofluorescence with the polyclonal antibody against mussel twitchin, a protein of thick filaments, and florescent phalloidin as a marker of filamentous cell actin were used to monitor changes in the developing muscle system at different larval stages. The first definitive muscle structures were found at the late trochophore stage (36 h after fertilization) and starting from the midveliger stage (96 h), striated muscles, which are never present in adult mussels, were distinctly seen. The striated muscle periodicity was 1.25 microm in both mussle larvae and adult scallop. The contractile activities of veliger and adult muscles were measured using an electronic signal-processing videosystem. This work is the first complex study of morphological, biochemical, and physiological characteristics of the muscle system in the larvae and adult mollusks.