Curious eroded depressions, most resembling an eye shedding an elongate tear, are found in gently sloping, intertidal, carbonate-rich arenite outcropping on the sea coast near Lakes Entrance, Victoria, southeast Australia. The depressions, known locally as Tears of the Virgin, are evidently formed by multiple generations of a barnacle, Chthamalus antennatus Darwin, 1854 in association with cyanobacteria. While the round part of a depression offers the barnacle a modicum of protection from impacts during high tides, it is also partially inhabited by cyanobacteria, which extend into and tend to fill the elongate tear. As such, this appears to be the first case of mutualism between a higher invertebrate and cyanobacteria, with the cyanobacteria reducing the barnacle's risk of desiccation while receiving metabolic wastes from it during low tides. It is also the first record of a balanomorph barnacle eroding calcareous arenite beneath its shell, the net effect of which would be expected to reduce its adhesion to the substrate. However, the siliceous residue, resulting from the barnacle's dissolution of the more than 80% of the calcite-rich sedimentary rock, is sequestered in delicate folds on the inside of the shell wall as it grows. A brief review of cirripedes capable of excavation includes the first photographic documentation of excavation of a mollusc shell by a verrucomorph.