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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 in some cases the shell is reduced such that the body cannot be retracted within it .
The anal sulcus, also called the anal sinus or anal canal, in Gastropods is a notch, a shelly tube at the top of the aperture. [1] It is the first notch close to the suture. It houses the anal siphon through which the snail expels water and waste products. Shell of Drillia poecila Sysoev & Bouchet, 2001, showing the anal sulcus on top of the ...
The shell of Semicassis pyrum has a large parietal callus, at the top in this image The shell of Cymatium pileare has a narrow parietal callus around the surface of the aperture nearest the columella, on the left of the shell opening as it is shown here. A parietal callus is a feature of the shell anatomy of some groups of snails, i.e. gastropods.
In other words, in gastropods whose shells have varices, the shells are characterised by episodic growth - the shell grows in spurts, and during the resting phase the varix forms. In many gastropod whose shells have varices, for example the Cassinae , the varix is essentially merely a thickening and swelling of the shell at that point.
The gastropod theory is now considered incorrect on the basis that there were no shell traces, nor many of the features usually found in gastropod shells such as ridges, and coils tapering to a point. Furthermore, the size of Dinocochlea is much larger than any other gastropod living or extinct. The coprolite theory is also considered incorrect ...
The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod.The apex is the first-formed, and therefore the oldest, part of the shell. [1] To be more precise, the apex would usually be where the tip of the embryonic shell or protoconch is situated, if that is still present in the adult shell (often it is lost or eroded away).
Siphonal indentations have evolved multiple times in gastropods and are widespread among many clades. Euomphanilae gastropods in the genus Scalites developed siphons in the early Ordovician period (448-443 MYA); however, they are not observed in any other members of the clade. 22 of an estimated >23 instances of siphonal indentations evolved in Murchosinoniinae gastropods - the two major ...
Most species of wentletrap are white, and have a porcelain-like appearance. They are notable for their intricately geometric shell architecture, and the shells of the larger species are prized by collectors. The more or less turret-shaped shell consists of tightly-wound (sometimes loosely coiled), convex whorls, which create a high, conical spiral.