Scanning electron microscope analysis of M. chuni giant basal spicule. (A) Cross section of spicule shows concentric lamellar arrangement of silica layers (la) around the central axial cylinder (cy). (B) Longitudinal section shows highly folded arrangement of the lamellae (la). (C) Immature spicules are encased within a collagen (col) net with a regular pattern of holes (h) where silica material is visible. (D) Lamellae in the spicule form protrusions which neatly fit into these holes. Reproduced with permission from [111, 116].
