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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 .
Turritellidae, with the common name "tower shells" or "tower snails", is a taxonomic family of small- to medium-sized sea snails, marine gastropod molluscs in the Sorbeoconcha clade. They are filter feeders; this method of feeding is somewhat unusual among gastropod mollusks, but is very common in bivalves.
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.
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 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 ...
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.
Scaly-foot gastropod Chrysomallon squamiferum, common name the scaly-foot gastropod, is a species of deep-sea hydrothermal-vent snail, a marine gastropod mollusc in the family Peltospiridae. This vent-endemic gastropod is known only from deep-sea hydrothermal vents in the Indian Ocean, where it has been found at depths of about 2,400–2,800 m ...
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 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 ...