FIGURE 19 in Deep-sea serpulids (Annelida: Polychaeta) in tetragonal tubes: on a tube convergence path from the Mesozoic to Recent

FIGURE 19. Tube ultrastructures of fossil tetragonal serpulid Tubulostium discoideum PIN 5485/24. A-E: longitudinal wall section, A—general view, B—enlarged outer part showing irregularly shaped crystals forming homogenous angular crystal (HAC) structure, C—enlarged axial part of parabolic growth lamellae showing simple prismatic (SP) structure, D—contact zone between outer layer and middle layer with homogenous granular (HG) structure, marked with non-rectilinear appearance of boundary between layers, E—internal wall part showing middle layer with HG structure and thin inner layer with slightly recrystallized simple prismatic (SP) or spherulitic prismatic (SPHP) structure; F-H: transverse section, F—view of sectioned spiral tube, G—view of wall cross-section through lateral side, H—same, through upper tube side. Abbreviations: o. s.—outer tube surface, i. s.—inner tube surface, c. l.—cementing layers, I—outer tube layer, II—middle tube layer, III—inner tube layer.