seashells come from?
If you have been to a beach, you may have noticed
the seashells everywhere. Sometimes, you can’t even walk through the
sand without shoes on for the sharp pieces. We know the seashells wash
up on shore from the ocean, but where do they come from before that?
Believe it or not, seashells are the outer cases of
a special type of sea animal called a mollusk, such as clams, snails and
mussels. Mollusks are a type of invertebrate animal, which means it
lacks a backbone, and other bones as well. The shell of a mollusk acts
as their skeleton outside of their bodies. It helps protect the
creatures from predators, strong currents and storms, helps camouflage
the animal, and do many other things. Seashells are primarily made of
calcium carbonate, a hard mineral, as our own bones are.
The shell comes from a body part that is special to
mollusks, called the mantle. It is the outside covering of the
soft-bodied mollusk. It secretes the calcium carbonate that hardens to
form the shell. The shell grows and gets larger as the animal grows and
The shape and color of shells vary greatly. Mostly,
shells serve to protect the tens of thousands of species of marine
mollusks. The hues of the shell are often influenced by the diet of the
mollusk, but some color pigments also serve an important structural
role, helping to reinforce the shell. A shell’s shape, size, and color
depend on the animal that made it and the purpose it serves.
Mollusks are divided into many types, but the two
major ones are bivalves and univalves. Bivalves are mollusks that have
two shell halves that form a whole shell, like a clam or oyster.
Univalves have one piece, usually a spiral, that makes up its whole
shell, which is usually more elaborate than a bivalve shell. Examples of
univalves are conch and nautilus.
When a mollusk dies, its shell is left behind, just
as land animals leave their skeletons behind. Sometimes, the shell is
used as a home by other sea creatures, such as hermit crabs. When a
hermit crab outgrows the shell it has borrowed, it abandons it and finds
a larger one to use. Sometimes, the shell washes up on the beach, where
we can look at them.