Agoniatitida are primitive ammonites that lived during Devonian times characterized by goniatitic sutures which have smooth elements and retrochoanitic ventral siphuncles that run along or close to the ventral margin and in which the septal necks point to the rear retaining the condition of their nautiloid ancestors. Shells vary in form depending on suborder and lower taxa. The number of sutural elements also varies accordingly. The Agoniatitida gave rise to the Goniatitida in the middle Devonian and to the Clymemiida, characterised by dorsal siphuncles, and Prolecanitida in the Late Devonian.