Some gastropods can also close the entrance to their shell with a tough operculum, a door-like structure which is attached to the dorsal surface of their foot. In evolutionary terms, the appearance of an operculum occurred shortly after that of torsion, which suggests a possible link with the role of torsion, though there is not sufficient evidence for or against this hypothesis.
Some gastropods can also shut their shell entrance with a robust operculum, a flap-like structure attached to the dorsal surface of their foot. In evolutionary terms, the appearance of an operculum occurred shortly after that of torsion, suggesting a possible connection between the two functions, although there is insufficient evidence to support or refute this hypothesis.