Abstract
We studied the body-wall musculature, its ECM (extracellular matrix), and the junctional complexes between muscle cells and between muscle cells and ECM in Macrostomum hystricinum marinum Rieger, 1977, using Nomarski-contrast and electron microscopy. Differentiation of these body-wall components was followed by monitoring embryonic stages at 52%, 64%, and 82% of the time between egg-laying and hatching and with study of the hatchling and adult stages. For comparison, the body-wall musculature of other macrostomidans has been examined in conventional light-histological sections.
Muscles form a grid of longitudinally, diagonally, and circularly oriented fibers beneath the epidermis in M. hystricinum marinum and this orientation of cells can be found already in embryos at 64% development. Younger embryos at 52% development show no muscle differentiation. The ECM forms a net-like arrangement that apparently envelops the individual muscle cells. Characteristic knob-like thickenings of the ECM occur at the base of the epidermis. Muscle cells attach to each other, to the epidermis, and to other cell types through hemidesmosome-like junctions at thickenings of the ECM in the adult and hatchling stages; no true desmosomes exist between muscle cells. Gap junctions occur commonly between longitudinal muscles of adult specimens and between perikarya of muscle cells in embryos at 64% and 82% development.
More comparative studies are needed to determine the systematic value of presence or absence of the diagonal muscle fibers in the body wall of turbellarians.
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Rieger, R., Salvenmoser, W., Legniti, A. et al. Organization and differentiation of the body-wall musculature in Macrostomum (Turbellaria, Macrostomidae). Hydrobiologia 227, 119–129 (1991). https://doi.org/10.1007/BF00027591
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DOI: https://doi.org/10.1007/BF00027591