Homes Under Water
Have you ever hunted for seashells at the beach? Did you know that they were once the homes of animals from a watery world?
This week, The Mini Page learns more about our world’s beautiful seashells.
A big family
Sea animals with shells belong to a group known as mollusks (Mah-lusks). Mollusks also include some animals with no shells, such as the octopus.
Protection
Shells help protect animals with soft bodies and no backbones, or vertebrae (Ver-tuh-bray). Soft-bodied animals with no backbone are called invertebrates (in-vertuh-brits). Most animals are invertebrates.
Seashells protect invertebrate sea animals. These marine animals, or creatures living in the water, build shell homes and live inside them. Some animals move into the shells of other animals after the original owner dies.
Building a home
Shells are made of a rocklike material formed from calcium and other minerals, like our bones are. Sea animals get these minerals from the water.
Shelled marine animals have a special skinlike covering over their bodies. This is called a mantle. The mantle secretes (SI-KREETS), or produces and spreads, the material for the shell all around the animal’s body.
Sea animals build their shells over time, layer by layer. You can tell how old a shellfish was by counting the layers spreading out over the shell, much like counting the rings of a tree. Shellfish don’t build their shells at a steady rate. They have growth spurts.
Colors
The beautiful colors on the shell vary depending on the animals’ diets and how fast they are secreting the shell material.
Shellfish in warmer waters, where there is a big variety of food, will usually have many more colors than shellfish in colder waters.
How many shells?
Animals such as snails build single shells to live in. Sea snails such as the conch or whelk usually build shells in a spiral shape.
Other mollusks, such as clams and oysters, have two shells joined together with a kind of hinge. This type of shellfish is called a bivalve (By-valve).
Have you noticed that you usually find only one half of a shell? When the animal dies or is eaten, the hinge usually breaks, and the two halves of the shell separate.
Shellfish life
Shellfish have a strawlike organ called a siphon (Sy-fun) that they use to pull water across their gills. They breathe and feed with their gills. They get their oxygen and food from the water.
Some shellfish also have a type of tiny plant called algae (AL- jee) living with them. The algae can make energy from sunlight and nutrients they get from the water. They share this energy with the shellfish.
Bivalves open their shells when they are eating or breathing. They close their shells when they feel threatened.
Shellfish that live in areas close to the coast may close their shells during low tide. This keeps the animal from drying out. When the tide comes back in, the animal opens up its house and lets the water in.
Collecting shells
Never take a shell that is home to a living animal. All living things are important to the environment.
Some living shellfish can sting you. The nose area of some cone shellfish has a kind of harpoon. They inject their prey with venom to paralyze it, then they eat it. Sometimes people can have serious reactions to the stings.