Pelecypoda (Bivalvia) are flat-footed, freshwater, equivalved mollusks with bilateral side symmetry, differing from Brachiopoda in shell symmetry, orientation, and beak characteristics.
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Crystallographic symmetry elements—zones and zone axes, center of symmetry (i), mirror planes (m), and rotation axes (n)—describe the geometric regularity of crystals and are fundamental for classifying crystal systems.
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Crystallographic projection converts a crystal’s 3D form into 2D representations—through spherical, gnomonic, orthographic, and especially stereographic projections—to analyze crystal face orientation and symmetry.
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