Fig. 3
From: The gladiuses in coleoid cephalopods: homology, parallelism, or convergence?
Comparative morphology of coleoid phragmocones (external and internal shell features are neglected). With dorsal proostracum (a Phragmoteuthida; b Belemnitida; c Diplobelida; d Groenlandibelidae); e without dorsal proostracum (e.g. Donovaniconida); f with reduced ventral wall (Sepiidae). Please note that the relative proostracum length of Groenlandibelidae is still unknown