The OPERCULUM ( trap door) that’s found on every Gastropod is a Cornelius or calcareous anatomical structure like a trapdoor that exists in many but not all groups of sea snails and the 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 of Helicindae,Cyclophoridae, Aciculudae, Maizaniidae, Pomatidae, etc. * * * Come shell with us let us help you find the Sh