The columella (meaning "little column") or (in older texts) pillar is a central anatomical feature of a coiled

snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class G ...

shell, a

gastropod shell 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 ...

. The columella is often only clearly visible as a structure when the shell is broken, sliced in half vertically, or viewed as an

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

image. The columella runs from the apex of the shell to the midpoint of the undersurface of the shell, or the tip of the siphonal canal in those shells which have a siphonal canal. If a snail shell is visualized as a cone of shelly material which is wrapped around a central axis, then the columella more or less coincides spatially with the central axis of the shell. In the case of shells that have an umbilicus, the columella is a hollow structure. The columella of some groups of gastropod shells can have a number of plications or folds (the columellar fold, plaits or plicae), which are usually visible when looking to the inner lip into the

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An ...

of the shell. These folds can be wide or narrow, prominent or subtle. These features of the columella are often useful in identifying the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

, or

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of the gastropod. The surface of the columella is called the columellar wall. The columellar callus is a smooth, calcareous thickening, secreted by the mantle, extending over the columellar area. The columellar lip, the visible part of the columella, is the lower part of the inner lip and is situated near the axis of coiling. A columellar tooth is a raised projection on the inner lip of a columella in the direction of the aperture. Czescimuszli shells tags

Columellar muscles

The soft parts of the body of the gastropod are held in place in the shell by the columellar muscles. These muscles are attached strongly to the columella itself not just far up in the apex of the shell but also by a long and narrow attachment over the length of a full whorl along the columella.Rebecca M. Price, ''Columellar Muscle of Neogastropods: Muscle Attachment and the Function of Columellar Folds,'' Biol.Bull. 205: 351–366.(December2003)
/ref> The columellar muscle passes underneath the mantle, greatly thickening the body wall, through the foot and is attached at its other end to inner face of the operculum (if present). The columellar muscles are contracted when the animal needs to withdraw the foot, head, and other soft parts into the shell for protection from drying out, and from predators. During these contractions the operculum and shell are approximated, and the animal is withdrawn within the latter.

George Washington Tryon George Washington Tryon Jr. (20 May 1838 – 5 February 1888) was an American malacologist who worked at the Academy of Natural Sciences in Philadelphia. Biography George Washington Tryon was the son of Edward K. Tryon and Adeline Savidt ...

, Structural and systematic conchology, 1882, p. 85 The columellar muscles are equally used to bring the soft body out of the shell. During protraction and retraction, the muscle twists, shortens or elongates. In very large gastropods such as the queen conch ( ''Aliger gigas'') once the columellar muscles are cut with a knife, the soft parts of the animal fall out of the shell easily. Conch fishermen in the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

break a small hole in the spire of the shell, cut the columellar muscles, and harvest the live meat of this species. Often the fishermen dump the empty shell back into the sea again.

References

* Columella listed in a glossar

* Another glossar

* A scholarly article on columellar muscles and columellar fold

External links

photo of cross section through shells
{{Gastropod anatomy Gastropod anatomy Mollusc shells