Symbiotic worms in the inner aragonitic layer of Leptodesma (Bivalvia) from the Přídolí (Upper Silurian) of Saaremaa Island, Estonia

Multiple calcareous worm-like boring casts occur on the inner surface of the calcitic external layer of the bivalve Leptodesma sp. from the Kaugatuma Formation (lower Pridoli, Upper Silurian) of Saaremaa Island, Estonia. Most of the boring casts are oriented with their apertures towards the posterior margin of Leptodesma sp. The worm-like casts were originally borings in the aragonitic layer of the valve. The borings were filled with sediment and the aragonitic layer of the bivalve later dissolved. The orientation of the borings indicates that they were likely made during the life of Leptodesma. The boring worms likely used the feeding currents of the bivalve to capture suspended nutrients, so they may have been kleptoparasites. Based on the morphology of borings in Leptodesma, they likely housed some type of filter-feeding polychaete annelid.