Search results
Results from the WOW.Com Content Network
These patterns, combined with minor variations in shell form, have led some conchologists to recognize 60 genera and hundreds of species and subspecies. In virtually all of the species in the family Cypraeidae, the shells are extremely smooth and shiny. This is because in the living animal, the shell is nearly always fully covered with the mantle.
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 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 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.
Tonna galea, commonly known as the giant tun, is a species of marine gastropod mollusc in the family Tonnidae (also known as the tun shells). This very large sea snail or tun snail is found in the North Atlantic Ocean as far as the coast of West Africa, in the Mediterranean Sea and the Caribbean Sea.
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 shell-less aplacophora have a chitinous cuticle that has been likened to the shell framework; it has been suggested that tanning of this cuticle, in conjunction with the expression of additional proteins, could have set the evolutionary stage for the secretion of a calcareous shell in an aplacophoran-like ancestral mollusc.
The body whorl shows in this side view as the last complete turn of the shell spiral, the part of the shell that leads up to the aperture. The body whorl is part of the morphology of the shell in those gastropod mollusks that possess a coiled shell. The term is also sometimes used in a similar way to describe the shell of a cephalopod mollusk.