FIGURE 4 in Deep-sea serpulids (Annelida: Polychaeta) in tetragonal tubes: on a tube convergence path from the Mesozoic to Recent

FIGURE 4. Tube ultrastructures of Spirodiscus grimaldii. A–J: PIN 5485/10, A—longitudinal wall section, B—enlarged outer part with a layer of crystals oriented in two directions subparallel to surface, C—enlarged middle wall part consisting of elongated crystals, D—enlarged inner wall part showing consolidated isometric crystals, E—tube cross-section, median rib clearly visible to the left, F—enlarged tube wall section through lateral keel, G—enlarged tube wall section through median keel, H—enlarged inner wall part, I—middle wall part, J—outer wall part, layer with two-direction crystal orientation resembling a pile of isometric crystals. Arrows indicate direction of tube growth. Abbreviation: o. s.—outer tube surface.