Cyclophoridae is a taxonomic family of small to large tropical land snails with an operculum, terrestrial gastropod mollusks in the order Architaenioglossa belonging to the subclass Caenogastropoda.
Cyclophoridae
†Archaeocyclotus plicatula in Burmese amber
The operculum is a corneous or calcareous anatomical structure like a trapdoor that exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails; the structure is found in some marine and freshwater gastropods, and in a minority of terrestrial gastropods, including the families Helicinidae, Cyclophoridae, Aciculidae, Maizaniidae, Pomatiidae, etc.
Shell of marine snail Lunella torquata with the calcareous operculum in place
Gastropod shell of the freshwater snail Viviparus contectus with corneous operculum in place
Penion sulcatus near Goat Island, New Zealand, with a damaged operculum
A photo of an individual of the freshwater snail species Bithynia tentaculata showing how the back of the shell rests on the round operculum on top of the foot as the snail moves along