A sea shell is a hard, protective outer layer created by an animal that lives in the sea.
The shell is part of the body of the animal.
Empty seashells are often found washed up on beaches by beachcombers.
The term seashell usually refers to the exoskeleton of an invertebrate which is an animal without a backbone.
Most shells that are found on beaches are the shells of marine mollusks, partly because many of these shells endure better than other seashells.
Seashells have been used by humans for many different purposes throughout history and pre-history.
Seashells are commonly found in beach drift, which is deposited along strandlines on beaches by the waves and the tides.
Shells are very often washed up onto a beach empty and clean, the animal having already died, and the soft parts having rotted away or having been eaten by either predators or scavengers.
Bivalves are often the most common seashells that wash up on large sandy beaches or in sheltered lagoons.
They can sometimes be extremely numerous. Very often the two valves become separated.
There are more than 15,000 species of bivalves that live in both marine and freshwater.
Examples of bivalves include clams, scallops, mussels, and oysters.
The majority of bivalves consist of two identical shells that are held together by a flexible hinge.
The animal's body is held protectively inside these two shells.
Bivalves that do not have two shells either have one shell or they lack a shell altogether.
The shells are made of calcium carbonate and are formed in layers by secretions from the mantle.
Bivalves are mostly filter feeders; through their gills, they draw in water, in which is trapped tiny food particles.
Some bivalves have eyes and an open circulatory system.
Bivalves are used all over the world as food and as a source of pearls.
Seashells have been used as a medium of exchange in various places, including many Indian Ocean and Pacific Ocean islands, also in North America, Africa and the Caribbean.
Seashells have often been used as tools, because of their strength and the variety of their shapes.
Giant clams have been used as bowls, and when big enough, even as bathtubs and baptismal fonts.
Many different species of bivalves have been used as scrapers, blades, clasps, and other such tools, due to their shape.
Some marine gastropods have been used for oil lamps, the oil being poured in the aperture of the shell, and the siphonal canal serving as a holder for the wick.
Because seashells are in some areas a readily available bulk source of calcium carbonate, shells such as oyster shells are sometimes used as soil conditioners in horticulture.
The shells are broken or ground into small pieces in order to have the desired effect of raising the pH and increasing the calcium content in the soil.
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