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.
This article describes a unique finding of an internal mold of Upper Devonian Cyclopoceras (formerly Cyclopites) abundans (Taxyceratidae, Discosorida) from Central Russia, which bears traces of possible parasite infestation (or, less probable, of a healed drilled hole). In the article a new generic replacement name Cyclopoceras is proposed for Devonian discosorid nautiloids, since Cyclopites is preoccupied by a generic name of Cambrian aglaspidid arthropod (Cyclopites Raasch 1939).
Unfortunately, in the discussion on possible drilling of the Cyclopoceras shell, I failed to mention a very interesting and important article Stridsberg, S. 1985. Silurian oncocerid cephalopods from Gotland. Fossils and Strata 18, 1–65 in which wonderful examples of bore holes in shells of Silurian oncocerides are described. This fact does not affect the conclusions of the article, but it is worth noting that demersal cephalopods such as oncocerids and discosorids had indeed been attacked by drilling predators.
Discosorida, Nautiloidea, Devonian, Parasites, Russia, Cyclopoceras