A number of benthic diatoms (including species of the genera Cocconeis, Achnanthes, and Amphora) etch shallow attachment scars in carbonate hard substrates. The morphology of these microbioerosion traces mirrors the elliptical to biconvex outline of the diatoms, which, in its most common appearance, is expressed as a distinct ring-shaped groove. The traces are established as new ichnogenus and -species Ophthalmichnus lyolithon. The diatoms are assumed to form the etching scars by means of their adhesive mucilage composed of acidic polysaccharides, probably in order to enhance adhesion.