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The periostracum, as well as the coloration, is only rarely preserved in fossil shells. The apertural end of the gastropod shell is the anterior end, nearest to the head of the animal; the apex of the spire is often the posterior end or at least is the dorsal side. Most authors figure the shells with the apex of the spire uppermost.
In gastropods, the body whorl, or last whorl, [1] is the most recently formed and largest whorl (or revolution) of a spiral or helical shell, terminating in the aperture.It is called the "body whorl" because most of the body of the soft parts of the animal fits into this whorl.
This shell has seven and a half whorls A fossil shell of the marine gastropod Turritella communis. This shell has nine whorls. A whorl is a single, complete 360° revolution or turn in the spiral or whorled growth of a mollusc shell. A spiral configuration of the shell is found in numerous gastropods, but it is also found in shelled cephalopods ...
A spire is part of the shell of a snail, a gastropod mollusc, a gastropod shell, and also the whorls of the shell in ammonites, which are fossil shelled cephalopods. In textbook illustrations of gastropod shells, the tradition (with a few exceptions) is to show most shells with the spire uppermost on the page.
For terms see gastropod shell. The 2-2.2 mm x 2-2.2 mm shell has a characteristic semispherical shape like a bee skep basket. The shell has 6 convex whorls which increase gradually in size. The sutures are deep. The whorls are decorated with very fine, very regular, radial ribs.
This is the largest extant snail (shelled gastropod) species in the world, and arguably the largest (heaviest) gastropod in the world. Although the shell itself is quite well known to shell collectors because of its extraordinary size, little is known about the ecology and behavior of the species, [ 7 ] except for one study about its feeding ...
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.
A varix is located at intervals around the whorl, and is formed by considerable thickening of the outer lip during a resting stage in the growth of the shell. 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.