Fig. 2
From: Jurassic ammonite aptychi: functions and evolutionary implications
Reconstruction of an ammonite with thick aptychus (Ap) having various functions. Saggital section based on modifications from Parent et al. (2014, based on Dzik 1981, Fig. 9a). a Partially retracted cephalic complex for resting and backwards swimming. b Projected cephalic complex with independently moving aptychus functioning as stabilizer by flapping in harmony with the jet pulse to prevent rocking, simultaneously acting as ballast and diving plane during forward and backward swimming. c Projected cephalic complex with independent aptychus flushing demersal prey, as well as acting as ballast and diving plane during forward swimming. Ct ctenidia, Rm paired retractor muscles, Ra radula. White arrows indicate direction of swimming