FIGURE 18 in Deep-sea serpulids (Annelida: Polychaeta) in tetragonal tubes: on a tube convergence path from the Mesozoic to Recent

FIGURE 18. Tube ultrastructures of fossil tetragonal serpulids from the Upper Cretaceous. A-D: Tetraditrupa rustica PIN 5485/22, A—longitudinal wall section, B—enlarged outer part with a layer of crystals oriented perpendicular to outer surface, C—enlarged middle wall part consisting of isometric crystals, D ‒ enlarged inner wall part. E-H: Tetraditrupa canteriata PIN 5485/05, E—longitudinal wall section, F—enlarged outer wall part showing elongated oriented crystals and isometric crystals near outer wall, G ‒ enlarged axial wall part made of small isometric crystals, H—enlarged inner wall part made of (?) partly recrystallised elongated oriented crystals. Arrows indicate direction of tube growth, and are placed along axis of parabolic growth lamellae, dashed line marks inner wall margin. Abbreviation: o. s.—outer tube surface.