periostracum

shell structure

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July 23, 2026

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The periostracum is a protective, chitinous outer layer that covers the exterior of the shells of many mollusks. It is particularly well-developed in freshwater mollusks and helps to prevent the shell from corroding. The shell itself is secreted by the mollusk's mantle and is composed of layers of conchiolin, calcite, and calcium carbonate. The periostracum is the outermost of these layers.123

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bivalve
The shell
The periostracum, the outermost organic layer, is secreted by the inner surface of the outer mantle fold at the mantle margin. It is a substrate upon which calcium carbonate can be deposited by the outer surface of the outer mantle fold. The number of calcareous layers…
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The periostracum, the outermost organic layer, is secreted by the inner surface of the outer mantle fold at the mantle margin. It is a substrate upon which calcium carbonate can be deposited by the outer surface of the outer mantle fold. The number of calcareous layers…
Read More

gastropod
The shell
The outer layer, or periostracum, is a mixture of proteins known as conchin. Inner layers of calcium carbonate interlace with a network of conchin and are impregnated with a variety of mineral salts. The calcium usually is in the form of calcite crystals in marine species and aragonite crystals…
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The outer layer, or periostracum, is a mixture of proteins known as conchin. Inner layers of calcium carbonate interlace with a network of conchin and are impregnated with a variety of mineral salts. The calcium usually is in the form of calcite crystals in marine species and aragonite crystals…
Read More