Tensile forces are transmitted longitudinally by the endto-end contacts across the Z-discs bounding the safcomeres and across the attachment plaques connecting between cell ends.
The detached sarcomeres remain interconnected serially like vertebrate myofibrils, through dense bodies and attachment plaques between cells.
During the developmental interval that I examined, I noted differences in the time when myofilaments appeared within cells of individual muscles, and changes in details of distal insertions, migration of shell attachment plaques, and differential expression of myocyte destruction programs.
At 52 hours, two myocytes of the LRM are noticeably larger than the other six, and these two alone make direct contact with shell field epithelial cells that will eventually form the attachment plaque onto the shell.
At 52 hours, the basal ends of these myocytes reach toward their definitive anchorage site on the protoconch, but a differentiated attachment plaque is not yet recognizable.