Whorl (mollusc)
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A whorl is a single, complete 360° revolution or turn in the spiral or whorled growth of a mollusc shell. A spiral configuration is found in the shells of numerous gastropods, and in shelled cephalopo
Counting gastropod whorls. In this example a shell with 3¾ whorls is shown, with the fourth whorl expanding more rapidly than whorls 1–3.
View of the spire side of the planispiral shell of the freshwater snail Anisus septemgyratus. This shell has seven and a half whorls
A fossil shell of the marine gastropod Turritella communis. This shell has nine whorls
The shell of the marine gastropod Haliotis asinina has fewer than two whorls
Protoconch
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A protoconch is an embryonic or larval shell which occurs in some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod. In older texts it is also called "nu
An SEM image of the trochophore of Haliotis asinina 11 hours post fertilization, with calcified protoconch (pc) prior to torsion.
Protoconch of Haliotis asinina when the torsion is complete.
Growth series of Caecum glabrum showing protoconch in bottom image.