Abstract
The fossil record of neritopsid opercula and shells shows that the shell shape typical for Neritopsidae and Neritidae appeared in the Triassic. The ancestors of Neritimorpha were most probably forms similar to Naticopsis. The operculum of Recent Neritopsis is composed of two calcitic parts secreted from inside and an aragonitic callus deposited from outside. Similar neritopsid opercula were already present in the Late Triassic. The first opercula with asymmetrically situated muscle scars, possibly ancestral for neritids, also appeared at that time.
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