FIGURE 16 in Deep-sea serpulids (Annelida: Polychaeta) in tetragonal tubes: on a tube convergence path from the Mesozoic to Recent

FIGURE 16. Tube ultrastructures of fossil tetragonal serpulids from the Middle Jurassic. A-D: Tetraserpula sp. 2 PIN 5485/ 19, A—longitudinal wall section, B—enlarged outer part showing large consolidated crystal aggregates, C—enlarged middle wall part containing isometrical crystals, D—enlarged inner wall part. E-H: Nogrobs tumidus PIN 5485/20, E—longitudinal wall section, F—enlarged outer wall part, G—enlarged middle wall part, H—enlarged inner wall part. Arrows indicate direction of tube growth and are placed along the axis of parabolic growth lamellae. Abbreviation: g. l.—growth lamellae; o. s.—outer surface of the tube.