 The shell is discoidal and very involute, with rapidly expanding and compressed whorls, fine radial ribs, a rounded venter with a shallow furrow, and almost closed umbilicus.Based on the examination of "O. pulcher" fossils from the Oligocene, the "Tremoctopus"–"Argonauta" divergence has been estimated to have occurred at least 29 million years ago.Two species are recognised in the genus.