Holes generated by tumbling experiments on various shells.
(A) Brachiopod shell (Frenulina sanguinolenta) (GIUS 12-3616/Fs1) after 4 hours of tumbling. (B) Unionidae bivalve shell (GIUS 12-3616/U1) after 1 hour of tumbling. (C–D) Gastropod shells (Nassarius sp.) (GIUS 12-3616/N1-2) after 2 hours of tumbling. (E–F) Close up of hole margins in Nassarius sp.