Definition

• Shells are the hard, protective coverings that are parts of many land and sea animals' bodies. The shells are exoskeletons protecting the creatures living inside. Shells are formed from an organism's natural growth of crystals. The shells grow as the animal or creature grows. Baby turtles burst from egg shells with tiny, soft shells approximately the size of golf balls, and some species grow as big as three feet or larger in shell diameter.
  
  

Human Use

• Humans began using seashells, snail shells, and even egg and turtle shells long ago for decorative and practical purposes. Pieces of jewelry or adornments for homes or clothing carved from various types of shells have existed for centuries. Decorated turtle shells helped make the first musical instruments. Ancient peoples cleaned out and removed the living organisms from the shells, and used them as containers for food and water. Humans have long consumed the contents of the shells and now consider them delicacies.
  
  

More Natural Uses

• Animals find their own uses for shells too. Hermit crabs use discarded mollusk shells for self-protection. These crabs find mollusk shells that are free of mollusk worms, and pack the shells on their backs to retreat into when predators approach. As the hermit crab grows, it will look for larger shells to use for protection.
  
  Eggshells also have a natural use. Farmers add ground eggshells to the feed of farm fowl, such as chickens or geese, to produce eggs with stronger, thicker shells. This makes for sturdier new eggs by preventing the shells from breaking as easily.
  
  

Mollusk Shells

• There are more than 50,000 varieties of mollusk shells. Some open like clam shells, while numerous others are spiraled with a single entrance hole. Many shells are particular to certain geographical areas or water types. For example, the conch, with it's distinctive shell, is found in tropical or subtropical areas and rarely washes ashore in cold climates--though they may be found as far north as the Carolinas.
  
  

Additional Information

• Certain shelled ocean creatures have the ability to alternate their genders for short spans of time. Shelled creatures lay eggs, which are also shell-covered. Some creatures are called shellfish because their entire bodies are covered by a thick shell. Shrimp, lobster and crab are examples of shellfish.