Mussel periostracum from the Florida Escarpment redox community (3266 m depth) is extensively bored by a variety of microorganisms. Four different types of pit borings were observed and characterized on the basis of SEM images of their resin casts, and/or light and TEM reconstructions: two large, open-pit borers, a “button” borer, and a cone borer. These boring patterns represent distinctive feeding “strategies”. The cumulative activities of periostracum borers remove the protective organic layer from the mussel shells, exposing the mineral to endolith attack.