The endolithic activity of Acetabularia acetabulum was documented on different lithotypes.
Morphology of the rhizoids was studied through microscopy observations.
Embedding casting procedure permitted the identification of the ichnospecies Fascichnus grandis.
Rhizoids of A. acetabulum penetrate several micrometres deep into marble and limestone.
Is here reported for the first time the role of A. acetabulum in the bioerosion of submerged artefacts.