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

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

shell, a

gastropod shell The gastropod shell is part of the body of many gastropods, including snails, 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 ...

. 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 (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

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 The siphonal canal is an anatomical feature of the shells of certain groups of sea snails within the clade Neogastropoda. Some sea marine gastropods have a soft tubular anterior extension of the mantle called a siphon through which water i ...

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, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...

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 ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

, or

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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 A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). In nature File:Photograph and axial plane floral diagra ...

along the columella.Rebecca M. Price, ''Columellar Muscle of Neogastropods: Muscle Attachment and the Function of Columellar Folds,'' Biol.Bull. 205: 351–366.(December 2003)
/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 is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

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