What are sea shells made of?
June 13, 2005
Shells are made of calcium carbonate,
a substance produced by a sea animal’s fleshy
mantle. As the animal grows, so does its shell.
Generally speaking, sea animals that produce shells are
called mollusks. Mollusks are a diverse group of invertebrates – animals
without backbones. They include one-shell animals (univalves),
like whelks, olives, and moon snails, and two-shelled animals
(bivalves), like clams, oysters and scallops. Oddly enough,
squid and octopus, which have no visible shells, are categorized
as mollusks, but that’s another column.
In general, scientists generally recognize seven different
classes of mollusks, consisting of some 130,000 species.
This easily makes them the second largest group of animals
in the world, outnumbered only by insects, and explains
the thousands upon thousands of shells you find on the
The body of a typical mollusk is pretty basic:
a fleshy mass that contains the digestive, excretory
and reproductive organs, covered by the fleshy
mantle. Some mollusks, however, have well-developed
heads, complete with eyes and a mouth, and a foot
for getting around.
No other animal group can compare with mollusks
for form, texture and pattern.
Their kaleidoscopic colors and endless variety
of sizes and shapes continue to amaze us whenever
we walk the beach.
Whelks, often called conchs, are single-shelled
snails that can grow very large. Their empty shells
are common on North Carolina’s barrier island
beaches. (Photo by John Mauser)
Shells have been used by many cultures for
many different purposes; jewelry, tools, in ceremonial
rites, as corporate logos, in home décor. Companies
have been named after them, science has derived medicines
from them, and industry has used them for road building
Early people used shells to make utensils, ornaments,
and even as currency. American Indians cut and polished
shells to make necklaces, or wove them into belts called
wampum, which they used for trading. The most valued wampum
came from the deep purple shells of the northern quahog
clam, one of North Carolina’s most common clams and
a popular seafood.