FIGURE 17 in Deep-sea serpulids (Annelida: Polychaeta) in tetragonal tubes: on a tube convergence path from the Mesozoic to Recent

FIGURE 17. Tube ultrastructures of fossil tetragonal serpulids from the Lower Cretaceous. A-D: Tetraserpula sp. 4 PIN 5485/ 21, A—longitudinal wall section, B—enlarged outer wall part showing isometric crystals forming homogenous granular (HG) ultrastructure, C—enlarged middle part consisting of isometric crystals, D—enlarged inner wall part. E-H: Tetraserpula barremica PIN 5485/07, E—longitudinal wall section showing a transition from prismatic crystals in outer wall to isometric in inner wall, F—enlarged outer (unaltered) wall part showing elongated oriented crystals near wall surface and isometric crystals near axial part of parabolic lamellae, G—enlarged axial wall part (slightly recrystallised) consisting mostly of small slightly elongated crystals, H—inner wall part (heavily recrystallised) consisting of small isometric crystals. Arrows indicate direction of tube growth and are placed along axis of parabolic growth lamellae. Abbreviation: o. s.—outer tube surface.