Gastropod shell
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 but may have a remnant within the mantle, or the shell is reduced such that the body cannot be retracted within. High-spired and highly sculptured forms become more common in quiet water environments.
About Gastropod shell in brief
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 but may have a remnant within the mantle, or the shell is reduced such that the body cannot be retracted within. Some shell shapes are found more often in certain environments, though there are many exceptions. High-spired and highly sculptured forms become more common in quiet water environments. The shell of burrowing forms, such as the olive and Terebra, are smooth, elongated, and lack elaborate sculpture, in order to decrease resistance when moving through sand. Most gastropod shells are spirally coiled. If a coiled shell is held with the spire pointing upwards and the aperture more or less facing the observer, a dextral shell will have the aperture on the right-hand side. A very few species show a mixture of dextRAL and sinistral individuals. Sinistrality arose independently 19 times among gastropODs at the start of the Cenozoic. But still the dextrals seem to account for 99% of the total number of living species in freshwater and land pulates. The left-handedness seems to be more common to more common snail species. A recent study correlates the asymmetric coiling of the shell by the left-right expression of the decapentaplegic gene in the mantle.
In a few cases, both left and right-handed snails are found in the same population of snails. The study of mollusc shells is known as conchology. Gastropod shell morphology is usually quite constant among individuals of a species. Controlling variables are: Some of these factors can be modelled mathematically and programs exist to generate extremely realistic images. The majority of species and genera are virtually alwaysSinistral, but a small minority of species show a very few. aberrantly sinistRAL forms of deextral species and some of these are highly sought by shell collectors. A few. species are rare in general among land snails but well documented among land. snails in general. The gastropoda shell has three major layers secreted by the mantle: the tracum, the periostracum and the nacre. The outermost layer is resistant to abrasion and provides most shell coloration. The body of the snail contacts the innermost smooth layer that may be composed of mother-of-pearl or shell nacre, a dense horizontally packed form of conchiolin, which is layered upon the peroastracum as the snail grows. The aperture is made of calcium carbonate precipitated into an organic matrix known as Conchiol in. This image was created by David Raup on the analog computer and is freely available at the Hathi Trust Digital Library.
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This page is based on the article Gastropod shell published in Wikipedia (as of Oct. 29, 2020) and was automatically summarized using artificial intelligence.
