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Molluscs are invertebrate animals (without a backbone) that have a soft body – molluscus, in Latin, means exactly “soft”. Most of them are equipped with a calcareous shell formed from a kind of skin that covers the body of these animals, called mantle or pallium. “The shell protects the animal and also works as a skeleton, supporting the body’s muscles for movement. It appears immediately after the birth of the larval stage. The larva, often smaller than 1 millimeter in diameter, forms a protective shell called a protoconch,” says biologist Osmar Domaneschi, from USP, who specializes in molluscs. The larval phase usually lasts for a short time, hours or days, depending on the species.
From there, the animal passes to the so-called juvenile phase, in which it already looks like an adult individual, with the difference that it is not yet sexually mature. “The juvenile mollusk continues to secrete substances that make up the shell, increasing it from the larval protoconch until it forms the definitive shell”, says Osmar.
The armor of these beings is formed by three layers
1. In this species of mollusc skin, called the mantle, the substances that will form the layers of the shell are secreted: calcium carbonate (extracted from sea water and food), amino acids and proteins (both produced by the animal’s own organism)
2. In contact with the mantle is the first layer of the shell, the lamellar layer, formed by calcium carbonate, crystallized in the form of blades. Its thickness continually increases as the mollusk grows, so it is the only layer that can be repaired by the animal.
3. The intermediate layer, prismatic, also has crystals of calcium carbonate, but in the form of prisms. It is produced only during shell growth. Therefore, if a part of the layer is damaged, it cannot be recovered.
4. The outermost part, the periostracum, is made up of amino acids and proteins. This layer protects the others against wear due to abrasion or acidic substances in the environment. It is also not regenerable