First possible evidence of parasite infestation in Upper Devonian Discosorida (Nautiloidea)

The small, but rather deep pit in the internal mould of the body chamber of Upper Devonian Cyclopoceras (nom. nov.) abundans (Taxyceratidae, Discosorida) from Central Russia is described in this paper. Similar pits are known to exist on internal moulds of Paleozoic cephalopod shells including nautiloids and Devonian ammonoids, and are interpreted as imprints of blister pearls: nacreous projections on the inner shell surface formed by mollusk for isolation of parasites. The pit studied herein corresponds with asymmetry of the muscle attachment scars and deformation of the last septum: the largest central pair of the muscle scars are shifted from the center of the ventral side, whereas the last septum is curved apically above the pit. These deformations indicate an abnormal growing of the shell at the latest stages of its development, giving a base for assumption that the pit was caused by a parasitic disease. The assumption of an appearance of this abnormality due to an attack by a drilling predator seems less likely. This finding is the first known possible imprint of blister pearls in Discosorida.