Home >> Science & Nature >> Insects & Science

Different Kinds of Shells

There are many animals that have shells. Some animals have soft shells, but others have rock-hard ones. The shells serve as the animal's main line of defense, and in some animals it also plays a functional role, serving as an attachment framework for muscles. Shells are not only used by these animals, but by humans as well. People have been using animal shells for thousands of years as ornaments, tools and protection.

Turtles, Tortoises
- Turtle and tortoise shells are called carapaces, which are made of hard bone plates covered by scutes. Scutes are made of keratin, which also forms hair, nails and hooves. Scutes have melanin, a pigment that is responsible for the patterns and colors found on shells. The inner layer of bone is what gives the shell its shape and strength, and it is fused with the ribs and spine to provide support. If the outer layer is breached by infection or injury, the turtle can develop an infection and die.
Gastropods
- Gastropods are mollusks, which are a type of invertebrate, or an animal without a backbone. There are more than 50,000 species of mollusks, and 70 percent of these are gastropods. Familiar examples of gastropods are snails and abalones. These shells are not only often beautiful, but functional. They are the animal's external skeleton and serve as protection for both snails and sea creatures and to keep snails from drying up in the sun. Snail shells are asymmetrical, while sea animal's shells are symmetrical. All the shells are comprised of three layers secreted from the animal's mantle and mostly made of calcium and chitin.
Bivalves
- Bivalves are animals with two shells held together by an elastic ligament. They are such a well known mollusk because we eat so many of them. Examples of these are clams, oysters, scallops and mussels. There are about 15,000 species of bivalves, and 80 percent are marine. Most bivalves do not move much, but instead attach themselves to the sea floor, seaweed or burrow in the sandy bottom. Clams, oysters and mussels make pearls when an irritant, like sand, is trapped inside and the animal. The animal then coats it with the same material used to make the inside of the shell.
Crustaceans
- Crustaceans are a type of arthropod, "arthro" meaning joint, and "pod" meaning leg. They, therefore, have highly developed legs for swimming and walking. Seventy-five percent of all animals are arthropods. Examples of crustaceans include shrimps, crabs, lobsters, prawns and barnacles. Their shells have between 16 and 60 segments made of calcium and protein, with thin, flexible joints so they can bend. As they grow, they must discard their shell and grow a new one. During this molting stage, without their shells they are very vulnerable and use their claws for protection.

Insects & Science