a Comparative Study of Ringiculidae and Acteonidae (Architectibranchia, Gastropoda) from the Campanian Amman Silicified Limestone Formation and some Similar Species from the Fringing Reefs of the Gulf of Aqaba in jordan

Two gastropod genera of Heterostropha and Architectibranchis were recorded from the Campanian Amman Silicified Limestone Formation. Representatives of these two gastropod genera are still living until now in the reef environment of the Gulf of Aqaba, and can be found near the Marine Biological Station of Jordan. An analytical comparison between the Campanian gastropods and the recent gastropods is attempted in the present study. The fossil shells have been transformed into silica and during this process of transformation from aragonite biocrystals of the crossed-lamellar structural type, they have retained the morphology of their micro-structure of crossed lamellae. The embryonic and larval shell of Acteon from the Cretaceous have the same size and morphology as that of the acteonid Pupa from Aqaba, and both also resemble each other regarding the adult shell morphology and ornament. The two genera of Ringicula recognized from Aqaba differ from each other predominantly regarding their size; one being larger than the other. They closely resemble the fossil Ringicula with some distinct characters of the inner lip of their aperture.