Arionoceras

Arionoceras is an extinct orthocerid genus from the Middle and Upper Silurian, of Europe that is estimated to have lived from 422.9 to 418.1 mya, existing for approximately.

Taxonomy

Arionoceras was named by Barskov and originally assigned to the Michelinoceratidae, but attributed by Serpagli and Gnoli -ibid to the Geisonoceratidae Zhuravleva "on the basis of the occurrence of a lining-like endosiphucular deposit." Dzik assigned Arionoceras to the newly proposed Arionoceratidae as the type genus. Sepkoski follows previous authors in putting Arionoceras in the Orthoceratida.

Morphology

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. The siphuncle is central with very short suborthochoanitic septal necks and cylindrical connecting rings. Apical chambers in adults have cameral deposits.