Fig. 7

Ultrastructure of the ventrolateral longitudinal muscle (mvl), parafrontal sections of the early metatrochophore of Siboglinum fiordicum. A The myoepithelial cells of the somatic longitudinal musculature form pseudo-multilayer (cells shown in different colors). Highly folded ECM (flo) along the contracted right ventrolateral longitudinal muscle (mvl). B Ultrastructure of the sarcomere of the striated muscles. C Hemidesmosomes (he) of the muscle fibers. D Site of the highly folded ECM (flo) of the septum and basal membrane of the myoepithelial cell: mvl from the trunk attaches to the ecm of the septum I. aj—adherens junction flo—finger-like outgrowths, he—hemidesmosomes, mf—longitudinal myofilaments, mls—longitudinal muscles of the first septum, mvl—ventrolateral longitudinal muscle strand, re—rough endoplasmic reticulum, sa—sarcomere, Zb—Z-bodies