A whorl is a single, complete 360° turn in the spiral growth of a molluscshell. A mollusc shell is basically a long tube, usually coiled in a spiral for strength and compactness. The number of whorls in the shell depend on various factors in the geometric growth, as described in work of D'Arcy Wentworth Thompson (On Growth and Form) and David Raup. In mathematics, a spiral is a curve which turns around some central point or axis, getting progressively closer to or farther from it, depending on which way you follow the curve. ... Classes Caudofoveata Aplacophora Polyplacophora - Chitons Monoplacophora Bivalvia - Bivalves Scaphopoda - Tusk shells Gastropoda - Snails and Slugs Cephalopoda - Squids, Octopuses, etc. ... Various seashells The hard, rigid outer calcium carbonate covering of certain animals is called a shell. ... DArcy Wentworth Thompson (May 2, 1860- June 21, 1948) was a biologist and mathematician and the author of the 1917 book, On Growth and Form, an influential work of striking originality. ... DArcy Wentworth Thompson (May 2, 1860- June 21, 1948) was a biologist and mathematician and the author of the 1917 book, On Growth and Form, an influential work of striking originality. ... David M. Raup is a University of Chicago paleontologist. ...
The number of whorls differs in various groups, with the extant family Turritellidae and the Mesozoic family Nerineidae having very high spired shells with a large number of whorls and hence a relatively small aperture. The Mesozoic is one of three geologic eras of Phanerozoic eon. ... The Spire in a mollusc shell constitutes all the whorls of a spiral shell exclusive except for the body whorl. ... Aperture is the opening in the shell of a gastropod, through which the snail emerges. ...
Apical whorls - those whorls near the apex or tip of the shell.
Body whorl - The most recently formed whorl of a spiral shell.
Nuclear whorl(s) - small, generally smooth whorls formed within the egg and constituting the apex of the shell.
Teleoconch - all the whorls of a shell after the protoconch.
The mollusc is a soft-bodied, usually shelled INVERTEBRATE belonging to one of the largest animal phyla (Mollusca) with some 100 000 living and about 35 000 FOSSIL species.
Molluscs are found on land and in salt and fresh water, and include SNAILS, ABALONE, CLAMS, MUSSELS, octopuses and squid.
Molluscs, because of their diverse and often beautiful shell shapes, accessibility, and importance as food and disease vectors, have played important cultural and economic roles in human history.
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