Reference Terms
from Wikipedia, the free encyclopedia
Animal shell
A shell is a hard, rigid outer layer, which has evolved in a very wide variety of different animals, including mollusks, sea urchins, crustaceans, turtles and tortoises, armadillos, etc. Scientific names for this type of structure include exoskeleton, test, carapace, and peltidium.
The shells that are perhaps most familiar and most commonly encountered, both in the wild and for sale as decorative objects, are seashells, more precisely, the external shells of marine mollusks. These are usually primarily composed of calcium carbonate, in the form of calcite or aragonite crystallised out in an organic matrix. Calcium carbonate in mollusc shells can take different crystalline forms, one being nacre otherwise known as mother of pearl.
Other kinds of animal shells are made from chitin, bone and cartilage, or silica.
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August 24, 2026
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Aug. 4, 2026 Animal bones preserved in South Australia’s underwater caves reveal distinctive clues shaped by darkness, algae, bacteria, and other environmental conditions. The findings give scientists a powerful new way to reconstruct how ancient megafauna ...
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Aug. 23, 2026 Scientists discovered a small, yellowish mountain horned dragon in Thailand and named it Acanthosaura syrax after a dragon from House of the Dragon. Found only in a narrow band of high-elevation ...
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Aug. 17, 2026 Scientists are searching some of Earth’s oldest rocks for tiny fossils that could reveal how simple microbial life made the extraordinary leap toward plants, animals, and other complex organisms. ...
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