The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where the head-foot part of the body of the animal emerges for locomotion, feeding, etc.
Three views of a shell of Norelona pyrenaica with the apertural view in the center
A shell of Semicassis pyrum, which has a large aperture and a pronounced parietal callus
Conus betulinus has a long and narrow aperture.
Indrella ampulla has an oval aperture.
The gastropod shell is part of the body of a gastropod or snail, a kind of mollusc. The shell is an exoskeleton, which protects from predators, mechanical damage, and dehydration, but also serves for muscle attachment and calcium storage. Some gastropods appear shell-less (slugs) but may have a remnant within the mantle, or in some cases the shell is reduced such that the body cannot be retracted within it (semi-slug). Some snails also possess an operculum that seals the opening of the shell, known as the aperture, which provides further protection. The study of mollusc shells is known as conchology. The biological study of gastropods, and other molluscs in general, is malacology. Shell morphology terms vary by species group.
Shells of two different species of sea snail: on the left is the normally sinistral (left-handed) shell of Neptunea angulata, on the right is the normally dextral (right-handed) shell of Neptunea despecta
The shell of a large land snail (probably Helix pomatia) with parts broken off to show the interior structure. 1 – umbilicus 2 – columellar plait 3 – aperture 4 – columella 5 – suture 6 – body whorl 7 – apex
Four views of a shell of Arianta arbustorum: Apertural view (top left), lateral view (top right), apical view (bottom left), and umbilical view (bottom right).
The left-handed turrid (Antiplanes vinosa)
