Fig. 9From: Ontogeny and morphology of the retrochoanitic septal necks of Agoniatites vanuxemi from the Middle Devonian Cherry Valley LimestoneSchematic representations of the septal necks contrasting the length of the dorsal and ventral sides of the septal necks through ontogeny. a Septal neck from the second whorl. The dorsal septal neck is only a little longer than the ventral septal neck. b In a later whorl the ventral side of the septal neck is much longer and extends into the next chamber. S siphuncle, VSN ventral septal neck, DSN dorsal septal neck, VW ventral shell wall, arrow indicates the adoral directionBack to article page