Arionoceras

Arionoceras was named by Barskov (1966)^[2] and originally assigned to the Michelinoceratidae, but attributed by Serpagli and Gnoli (1977) -ibid to the Geisonoceratidae Zhuravleva (1959) "on the basis of the (admittedly irregular) occurrence of a lining-like endosiphucular deposit." Dzik (1984) assigned Arionoceras to the newly proposed Arionoceratidae as the type genus. Sepkoski (2002)^[3] follows previous authors in putting Arionoceras in the Orthoceratida.

Arionoceras has a straight or slightly curved shell with a circular or depressed cross section, smooth or transversely sculptured surface, and large apically pointed protoconch.^[2] The siphuncle is central with very short suborthochoanitic septal necks and cylindrical connecting rings. Apical chambers in adults have cameral deposits.