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Porosity of the coralligenous concretion. A Holes and cavities of the coralligenous concretion B Magnification of the holes C Magnification of a natural hole occupied by spicules of Pachastrella monilifera D Spicules of Jaspis johnstoni in a natural cavity in the coralligenous concretion E Cavity excavated by a boring sponge with excavation marks (pits) on the wall F Border between the area excavated by a boring sponge (right) and the not excavated area (left).
