Fig. 5

Agoniatites vanuxemi. Septal necks. a, b PRI 68137. a Septal neck in second whorl. Dorsal side of septal neck is well preserved. Auxiliary deposits on the dorsal and ventral sides of neck extend adapically beyond the end of the septal neck. Septum split by calcite seam below dorsal side of septal neck. Scale bar 200 μm. b Another septal neck in the second whorl. Auxiliary deposits are well preserved on dorsal and ventral sides. Scale bar 100 μm. c AMNH 53356. Septal neck with organic membranes extending across siphuncle. Scale bar 100 μm. d–f PRI 68138. d Well-preserved septal neck from second whorl. Scale bar 30 μm. e Close-up from d. Ventral side of septal neck with auxiliary deposit preserved. Scale bar 10 μm. f Dorsal side of septal neck with well-preserved auxiliary deposit. Scale bar 10 μm. S septum, V venter, DSN dorsal part of septal neck, VSN ventral part of septal neck, aux auxiliary deposits, arrow adoral direction